Bug 1766045 - Vendoring in Rust code for uniffi-bindgen-gecko-js r=glandium,supply-chain-reviewers

- Added `--enable-uniffi-fixtures` flag. When set, we will compile in the UniFFI test fixtures into our shared Rust crate and eventually into `libxul`. - Vendoring in the Rust crates needed for `uniffi-bindgen-gecko-js` Differential Revision: https://phabricator.services.mozilla.com/D144467
2022-08-03 18:59:36 +00:00 · 2022-08-03 18:59:36 +00:00 · fd4cfd1807
--- a/.cargo/config.in
+++ b/.cargo/config.in
@ -12,6 +12,11 @@ git = "https://github.com/rust-minidump/minidump-writer.git"
 replace-with = "vendored-sources"
 rev = "75ada456c92a429704691a85e1cb42fef8cafc0d"

+[source."https://github.com/mozilla/uniffi-rs.git"]
+git = "https://github.com/mozilla/uniffi-rs.git"
+replace-with = "vendored-sources"
+rev = "bb2039f077a29dba0879372a67e764e6ace8e33f"
+
 [source."https://github.com/mozilla/neqo"]
 git = "https://github.com/mozilla/neqo"
 replace-with = "vendored-sources"
--- a/Cargo.lock
+++ b/Cargo.lock
@ -1549,6 +1549,18 @@ dependencies = [
 "serde",
 ]

+[[package]]
+name = "extend"
+version = "1.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c5216e387a76eebaaf11f6d871ec8a4aae0b25f05456ee21f228e024b1b3610"
+dependencies = [
+ "proc-macro-error",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "fallible-iterator"
 version = "0.2.0"
@ -2164,6 +2176,11 @@ dependencies = [
 "tokio-threadpool",
 "unic-langid",
 "unic-langid-ffi",
+ "uniffi-example-arithmetic",
+ "uniffi-example-geometry",
+ "uniffi-example-rondpoint",
+ "uniffi-example-sprites",
+ "uniffi-example-todolist",
 "url",
 "viaduct",
 "webext_storage_bridge",
@ -5602,6 +5619,75 @@ dependencies = [
 "log",
 "paste",
 "static_assertions",
+ "uniffi_bindgen",
+]
+
+[[package]]
+name = "uniffi-bindgen-gecko-js"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "askama",
+ "camino",
+ "clap",
+ "extend",
+ "heck",
+ "serde",
+ "toml 0.5.9",
+ "uniffi_bindgen",
+]
+
+[[package]]
+name = "uniffi-example-arithmetic"
+version = "0.18.0"
+source = "git+https://github.com/mozilla/uniffi-rs.git?rev=bb2039f077a29dba0879372a67e764e6ace8e33f#bb2039f077a29dba0879372a67e764e6ace8e33f"
+dependencies = [
+ "thiserror",
+ "uniffi",
+ "uniffi_build",
+ "uniffi_macros",
+]
+
+[[package]]
+name = "uniffi-example-geometry"
+version = "0.18.0"
+source = "git+https://github.com/mozilla/uniffi-rs.git?rev=bb2039f077a29dba0879372a67e764e6ace8e33f#bb2039f077a29dba0879372a67e764e6ace8e33f"
+dependencies = [
+ "uniffi",
+ "uniffi_build",
+ "uniffi_macros",
+]
+
+[[package]]
+name = "uniffi-example-rondpoint"
+version = "0.18.0"
+source = "git+https://github.com/mozilla/uniffi-rs.git?rev=bb2039f077a29dba0879372a67e764e6ace8e33f#bb2039f077a29dba0879372a67e764e6ace8e33f"
+dependencies = [
+ "uniffi",
+ "uniffi_build",
+ "uniffi_macros",
+]
+
+[[package]]
+name = "uniffi-example-sprites"
+version = "0.18.0"
+source = "git+https://github.com/mozilla/uniffi-rs.git?rev=bb2039f077a29dba0879372a67e764e6ace8e33f#bb2039f077a29dba0879372a67e764e6ace8e33f"
+dependencies = [
+ "uniffi",
+ "uniffi_build",
+ "uniffi_macros",
+]
+
+[[package]]
+name = "uniffi-example-todolist"
+version = "0.18.0"
+source = "git+https://github.com/mozilla/uniffi-rs.git?rev=bb2039f077a29dba0879372a67e764e6ace8e33f#bb2039f077a29dba0879372a67e764e6ace8e33f"
+dependencies = [
+ "lazy_static",
+ "thiserror",
+ "uniffi",
+ "uniffi_build",
+ "uniffi_macros",
 ]

 [[package]]
--- a/Cargo.toml
+++ b/Cargo.toml
@ -165,3 +165,16 @@ path = "third_party/rust/mio-0.6.23"
 # https://github.com/mozilla/neqo/pull/1350
 [patch."https://github.com/mozilla/neqo"]
 neqo-common = { path = "third_party/rust/neqo-common" }
+
+# These are used to test UniFFI functionality.  We haven't figured out how we
+# want to publish these yet, so they are only accessible via git.  This works
+# okay, but it means that their dependencies on UniFFI crates will normally
+# also be the git versions.  Patch them to use the published versions to avoid
+# duplicate crates.
+
+[patch."https://github.com/mozilla/uniffi-rs.git"]
+uniffi = "0.19"
+uniffi_bindgen = "0.19"
+uniffi_build = "0.19"
+uniffi_macros = "0.19"
+weedle2 = "3.0.0"
--- a/supply-chain/audits.toml
+++ b/supply-chain/audits.toml
@ -99,6 +99,12 @@ criteria = "safe-to-deploy"
 delta = "0.4.0 -> 0.5.0"
 notes = "The repository for this crate belongs in the Mozilla org."

+[[audits.extend]]
+who = "Ben Dean-Kawamura <bdk@mozilla.com>"
+criteria = "safe-to-deploy"
+version = "1.1.2"
+notes = "Inspected the crate and noted that the impl block comes directly from the proc-macro input.  If no new code can be added by this crate, I don't think there can be any issues."
+
 [[audits.flagset]]
 who = "Ryan Hunt <rhunt@eqrion.net>"
 criteria = "safe-to-deploy"
--- a/third_party/rust/extend/.cargo-checksum.json
+++ b/third_party/rust/extend/.cargo-checksum.json
@ -0,0 +1 @@
+{"files":{"CHANGELOG.md":"910cd2057d356b18cd4f21791bc23956734a83b0f58701ec0d0d03405f5c21df","Cargo.toml":"928b8b97607b3589b85a6d4d00fb1cf64b78bee6354c303d8f49fbfa2ca5bdae","LICENSE":"db0efd0bb80126f32214f478434536d07d86a30658fb209d8b543b7261492a2b","README.md":"0872b2b15ec22732a09b121a31cdd8f8cfc80566f671566e4a7fb6b52a742a2e","deny.toml":"60448e9313f1883a7adf30713fcca789c454e77228105926024ce3abe9293100","rustfmt.toml":"9bbb759b3914c49c8060bcdeeb7786f4aec083d30bcfe236bbd48d8388d06103","src/lib.rs":"85bd23c064c78dcd141cb2fecca6fff2ee7e1dfb4cf19b74ab97ef30d51f6f03","tests/compile_fail/double_vis.rs":"524e8bc996f5a45de3d15f0c741d4f3414004e9c636c52de0f011785cc535109","tests/compile_fail/double_vis.stderr":"3748e67e6f41bd5624946ad7cdc4e2b30a9d0b5e76bc27c19ecc9d62da733978","tests/compile_fail/supertraits_are_actually_included.rs":"c03980316c4e71ceb7e80ab7011f00b6f1f8f89906670e9823267a4118f72853","tests/compile_fail/supertraits_are_actually_included.stderr":"835e79bb1bceb48e9db5f0a410c57af51c856e17917ef72f65e3ae2af79d97ec","tests/compile_pass/associated_constants.rs":"f3e56405650ddd31c33e932846553e88fe7181585e0f09a7414d50d521b0f103","tests/compile_pass/async_trait.rs":"9138801d67dbe20ed87fdb3f48bb968f0bfa11fe2d27414d5ea5ea7a6e44bb35","tests/compile_pass/changing_extension_trait_name.rs":"046e7a66151ce05c3515b4bea36be72f83b98f3bdb06fa6f065ad6fc373e19f2","tests/compile_pass/complex_trait_name.rs":"5a8c3588c26df07973739fbb85619d0de480cc8c992611dfc2dbcb9ab3c6e2b6","tests/compile_pass/double_ext_on_same_type.rs":"0e4d16fe9059f0325e4ad1337d53738876633b0533f9a2d4e9714ddada96eb4d","tests/compile_pass/extension_on_complex_types.rs":"88bdf979e1f399d7f9824165730b33884bc9c46347d246f8cc12e0e2039642a1","tests/compile_pass/generics.rs":"367f089e8010d1c98ccc975b03acb6cf03810793e1198105f75c006eafd52bb8","tests/compile_pass/hello_world.rs":"1961cfa634143974f0d64b26f817ac3148375faa5cf5864d63f0127d3af8099e","tests/compile_pass/issue_2.rs":"a14d5e2179b74ff71c5357e8a4f1a9ac228a711196edd40c12719565c8dfaa21","tests/compile_pass/more_than_one_extension.rs":"1d7486e4e9e4095d7e7f42aac878d836f021c49fbe26c31cb13fe6a0415a8558","tests/compile_pass/multiple_config.rs":"dc3b06e4fafbb7236b5bc49f9a5e9693241c07118da8886dd0752b895ff27425","tests/compile_pass/multiple_generic_params.rs":"2ac052ea7b818b6d45ee8070cf6ec18953419473f711375cafbe7283244b5743","tests/compile_pass/pub_impl.rs":"8dfcba21fbbc45efcf85b66fca2d187022569e72d4b10b57047eddda67a1725b","tests/compile_pass/ref_and_ref_mut.rs":"d1086a23809cbd8f87487677073238c3657a8a98fafc63a688eb9d622bf2eb11","tests/compile_pass/sized.rs":"baceaaabcf368b3c72e6d27fea72aadde11d97d9d153c35df5e2d89fb3da4e3e","tests/compile_pass/super_trait.rs":"07448e1fe2b9018125ccaabf7db1e2a244788519bb42117f8e437e48358eb2f0","tests/compile_pass/visibility_config.rs":"64846014a63327661fb250cdb726cce532ed82b1cea5cb83308526bcba22b4be"},"package":"5c5216e387a76eebaaf11f6d871ec8a4aae0b25f05456ee21f228e024b1b3610"}
--- a/third_party/rust/extend/CHANGELOG.md
+++ b/third_party/rust/extend/CHANGELOG.md
@ -0,0 +1,79 @@
+# Change Log
+
+All user visible changes to this project will be documented in this file.
+This project adheres to [Semantic Versioning](http://semver.org/), as described
+for Rust libraries in [RFC #1105](https://github.com/rust-lang/rfcs/blob/master/text/1105-api-evolution.md)
+
+## Unreleased
+
+None.
+
+### Breaking changes
+
+None.
+
+## 1.1.2 - 2021-09-02
+
+- Fix using `pub impl` with `#[async_trait]`.
+
+## 1.1.1 - 2021-06-12
+
+- Fix name collision for extensions on `&T` and `&mut T`. The generated traits
+  now get different names.
+
+## 1.1.0 - 2021-06-12
+
+- Support setting visibility of the generated trait directly on the `impl`
+  block. For example: `pub impl i32 { ... }`.
+- Add `#[ext_sized]` for adding `Sized` supertrait.
+
+## 1.0.1 - 2021-02-14
+
+- Update maintenance status.
+
+## 1.0.0 - 2021-01-30
+
+- Support extensions on bare functions types (things like `fn(i32) -> bool`).
+- Support extensions on trait objects (things like `dyn Send + Sync`).
+
+## 0.3.0 - 2020-08-31
+
+- Add async-trait compatibility.
+
+### Breaking changes
+
+- Other attributes put on the `impl` would previously only be included on the generated trait. They're now included on both the trait and the implementation.
+
+## 0.2.1 - 2020-08-29
+
+- Fix documentation link in Cargo.toml.
+- Use more correct repository URL in Cargo.toml.
+
+## 0.2.0 - 2020-08-29
+
+- Handle unnamed extensions on the same generic type with different type parameters. For example `Option<i32>` and `Option<String>`. Previously we would generate the same name of both hidden traits which wouldn't compile.
+- Support associated constants in extension impls.
+
+### Breaking changes
+
+- Generated traits are no longer sealed and the `sealed` argument previously supported by `#[ext]` has been removed. Making the traits sealed lead to lots of complexity that we didn't think brought much value.
+
+## 0.1.1 - 2020-02-22
+
+- Add support for specifying supertraits of the generated trait [#4](https://github.com/davidpdrsn/extend/pull/4).
+
+## 0.1.0
+
+- Support adding extensions to the ["never type"](https://doc.rust-lang.org/std/primitive.never.html).
+
+### Breaking changes
+
+- Simplify names of traits generates for complex types.
+
+## 0.0.2
+
+- Move "trybuild" to dev-dependency.
+
+## 0.0.1
+
+Initial release.
--- a/third_party/rust/extend/Cargo.toml
+++ b/third_party/rust/extend/Cargo.toml
@ -0,0 +1,48 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies
+#
+# If you believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+edition = "2018"
+name = "extend"
+version = "1.1.2"
+authors = ["David Pedersen <david.pdrsn@gmail.com>"]
+description = "Create extensions for types you don't own with extension traits but without the boilerplate."
+homepage = "https://github.com/davidpdrsn/extend"
+documentation = "https://docs.rs/extend"
+readme = "README.md"
+keywords = ["extension", "trait"]
+categories = ["rust-patterns"]
+license = "MIT"
+repository = "https://github.com/davidpdrsn/extend.git"
+
+[lib]
+path = "src/lib.rs"
+proc-macro = true
+[dependencies.proc-macro-error]
+version = "1"
+
+[dependencies.proc-macro2]
+version = "1"
+
+[dependencies.quote]
+version = "1"
+
+[dependencies.syn]
+version = "1"
+features = ["full", "extra-traits", "visit"]
+[dev-dependencies.async-trait]
+version = "0.1.40"
+
+[dev-dependencies.trybuild]
+version = "1.0.17"
+[badges.maintenance]
+status = "passively-maintained"
--- a/third_party/rust/extend/LICENSE
+++ b/third_party/rust/extend/LICENSE
@ -0,0 +1,19 @@
+MIT License Copyright (c) 2020 David Pedersen
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is furnished
+to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice (including the next
+paragraph) shall be included in all copies or substantial portions of the
+Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS
+OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF
+OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
--- a/third_party/rust/extend/README.md
+++ b/third_party/rust/extend/README.md
@ -0,0 +1,32 @@
+# extend
+
+[![Crates.io](https://img.shields.io/crates/v/extend.svg)](https://crates.io/crates/extend)
+[![Docs](https://docs.rs/extend/badge.svg)](https://docs.rs/extend)
+[![dependency status](https://deps.rs/repo/github/davidpdrsn/extend/status.svg)](https://deps.rs/repo/github/davidpdrsn/extend)
+[![Build status](https://github.com/davidpdrsn/extend/workflows/CI/badge.svg)](https://github.com/davidpdrsn/extend/actions)
+![maintenance-status](https://img.shields.io/badge/maintenance-passively--maintained-yellowgreen.svg)
+
+Create extensions for types you don't own with [extension traits] but without the boilerplate.
+
+Example:
+
+```rust
+use extend::ext;
+
+#[ext]
+impl<T: Ord> Vec<T> {
+    fn sorted(mut self) -> Self {
+        self.sort();
+        self
+    }
+}
+
+fn main() {
+    assert_eq!(
+        vec![1, 2, 3],
+        vec![2, 3, 1].sorted(),
+    );
+}
+```
+
+[extension traits]: https://dev.to/matsimitsu/extending-existing-functionality-in-rust-with-traits-in-rust-3622
--- a/third_party/rust/extend/deny.toml
+++ b/third_party/rust/extend/deny.toml
@ -0,0 +1,47 @@
+targets = []
+
+[advisories]
+db-path = "~/.cargo/advisory-db"
+db-urls = ["https://github.com/rustsec/advisory-db"]
+vulnerability = "deny"
+unmaintained = "warn"
+yanked = "warn"
+notice = "warn"
+ignore = []
+
+[licenses]
+unlicensed = "deny"
+allow = [
+    "MIT",
+    "Apache-2.0",
+]
+deny = []
+copyleft = "warn"
+allow-osi-fsf-free = "neither"
+default = "deny"
+confidence-threshold = 0.8
+exceptions = []
+
+[licenses.private]
+ignore = false
+registries = []
+
+[bans]
+multiple-versions = "deny"
+wildcards = "allow"
+highlight = "all"
+allow = []
+deny = []
+skip = []
+skip-tree = []
+
+[sources]
+unknown-registry = "warn"
+unknown-git = "warn"
+allow-registry = ["https://github.com/rust-lang/crates.io-index"]
+allow-git = []
+
+[sources.allow-org]
+github = []
+gitlab = []
+bitbucket = []
--- a/third_party/rust/extend/rustfmt.toml
+++ b/third_party/rust/extend/rustfmt.toml
@ -0,0 +1 @@
+merge_imports = true
--- a/third_party/rust/extend/src/lib.rs
+++ b/third_party/rust/extend/src/lib.rs
@ -0,0 +1,620 @@
+//! Create extensions for types you don't own with [extension traits] but without the boilerplate.
+//!
+//! Example:
+//!
+//! ```rust
+//! use extend::ext;
+//!
+//! #[ext]
+//! impl<T: Ord> Vec<T> {
+//!     fn sorted(mut self) -> Self {
+//!         self.sort();
+//!         self
+//!     }
+//! }
+//!
+//! fn main() {
+//!     assert_eq!(
+//!         vec![1, 2, 3],
+//!         vec![2, 3, 1].sorted(),
+//!     );
+//! }
+//! ```
+//!
+//! # How does it work?
+//!
+//! Under the hood it generates a trait with methods in your `impl` and implements those for the
+//! type you specify. The code shown above expands roughly to:
+//!
+//! ```rust
+//! trait VecExt<T: Ord> {
+//!     fn sorted(self) -> Self;
+//! }
+//!
+//! impl<T: Ord> VecExt<T> for Vec<T> {
+//!     fn sorted(mut self) -> Self {
+//!         self.sort();
+//!         self
+//!     }
+//! }
+//! ```
+//!
+//! # Supported items
+//!
+//! Extensions can contain methods or associated constants:
+//!
+//! ```rust
+//! use extend::ext;
+//!
+//! #[ext]
+//! impl String {
+//!     const CONSTANT: &'static str = "FOO";
+//!
+//!     fn method() {
+//!         // ...
+//!         # todo!()
+//!     }
+//! }
+//! ```
+//!
+//! # Configuration
+//!
+//! You can configure:
+//!
+//! - The visibility of the trait. Use `pub impl ...` to generate `pub trait ...`. The default
+//! visibility is private.
+//! - The name of the generated extension trait. Example: `#[ext(name = MyExt)]`. By default we
+//! generate a name based on what you extend.
+//! - Which supertraits the generated extension trait should have. Default is no supertraits.
+//! Example: `#[ext(supertraits = Default + Clone)]`.
+//!
+//! More examples:
+//!
+//! ```rust
+//! use extend::ext;
+//!
+//! #[ext(name = SortedVecExt)]
+//! impl<T: Ord> Vec<T> {
+//!     fn sorted(mut self) -> Self {
+//!         self.sort();
+//!         self
+//!     }
+//! }
+//!
+//! #[ext]
+//! pub(crate) impl i32 {
+//!     fn double(self) -> i32 {
+//!         self * 2
+//!     }
+//! }
+//!
+//! #[ext(name = ResultSafeUnwrapExt)]
+//! pub impl<T> Result<T, std::convert::Infallible> {
+//!     fn safe_unwrap(self) -> T {
+//!         match self {
+//!             Ok(t) => t,
+//!             Err(_) => unreachable!(),
+//!         }
+//!     }
+//! }
+//!
+//! #[ext(supertraits = Default + Clone)]
+//! impl String {
+//!     fn my_length(self) -> usize {
+//!         self.len()
+//!     }
+//! }
+//! ```
+//!
+//! For backwards compatibility you can also declare the visibility as the first argument to `#[ext]`:
+//!
+//! ```
+//! use extend::ext;
+//!
+//! #[ext(pub)]
+//! impl i32 {
+//!     fn double(self) -> i32 {
+//!         self * 2
+//!     }
+//! }
+//! ```
+//!
+//! # async-trait compatibility
+//!
+//! Async extensions are supported via [async-trait](https://crates.io/crates/async-trait).
+//!
+//! Be aware that you need to add `#[async_trait]` _below_ `#[ext]`. Otherwise the `ext` macro
+//! cannot see the `#[async_trait]` attribute and pass it along in the generated code.
+//!
+//! Example:
+//!
+//! ```
+//! use extend::ext;
+//! use async_trait::async_trait;
+//!
+//! #[ext]
+//! #[async_trait]
+//! impl String {
+//!     async fn read_file() -> String {
+//!         // ...
+//!         # todo!()
+//!     }
+//! }
+//! ```
+//!
+//! # Other attributes
+//!
+//! Other attributes provided _below_ `#[ext]` will be passed along to both the generated trait and
+//! the implementation. See [async-trait compatibility](#async-trait-compatibility) above for an
+//! example.
+//!
+//! [extension traits]: https://dev.to/matsimitsu/extending-existing-functionality-in-rust-with-traits-in-rust-3622
+
+#![doc(html_root_url = "https://docs.rs/extend/1.1.2")]
+#![allow(clippy::let_and_return)]
+#![deny(
+    unused_variables,
+    mutable_borrow_reservation_conflict,
+    dead_code,
+    unused_must_use,
+    unused_imports
+)]
+
+use proc_macro2::TokenStream;
+use proc_macro_error::*;
+use quote::{format_ident, quote, ToTokens};
+use syn::{
+    parse::{self, Parse, ParseStream},
+    parse_macro_input, parse_quote,
+    punctuated::Punctuated,
+    spanned::Spanned,
+    token::{Add, Semi},
+    Ident, ImplItem, ItemImpl, Token, TraitItemConst, TraitItemMethod, Type, TypeArray, TypeBareFn,
+    TypeGroup, TypeNever, TypeParamBound, TypeParen, TypePath, TypePtr, TypeReference, TypeSlice,
+    TypeTraitObject, TypeTuple, Visibility,
+};
+
+#[derive(Debug)]
+struct Input {
+    item_impl: ItemImpl,
+    vis: Option<Visibility>,
+}
+
+impl Parse for Input {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let mut attributes = Vec::new();
+        if input.peek(syn::Token![#]) {
+            attributes.extend(syn::Attribute::parse_outer(input)?);
+        }
+
+        let vis = input
+            .parse::<Visibility>()
+            .ok()
+            .filter(|vis| vis != &Visibility::Inherited);
+
+        let mut item_impl = input.parse::<ItemImpl>()?;
+        item_impl.attrs.extend(attributes);
+
+        Ok(Self { item_impl, vis })
+    }
+}
+
+/// See crate docs for more info.
+#[proc_macro_attribute]
+#[proc_macro_error]
+#[allow(clippy::unneeded_field_pattern)]
+pub fn ext(
+    attr: proc_macro::TokenStream,
+    item: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    let item = parse_macro_input!(item as Input);
+    let config = parse_macro_input!(attr as Config);
+    go(item, config)
+}
+
+/// Like [`ext`](macro@crate::ext) but always add `Sized` as a supertrait.
+///
+/// This is provided as a convenience for generating extension traits that require `Self: Sized`
+/// such as:
+///
+/// ```
+/// use extend::ext_sized;
+///
+/// #[ext_sized]
+/// impl i32 {
+///     fn requires_sized(self) -> Option<Self> {
+///         Some(self)
+///     }
+/// }
+/// ```
+#[proc_macro_attribute]
+#[proc_macro_error]
+#[allow(clippy::unneeded_field_pattern)]
+pub fn ext_sized(
+    attr: proc_macro::TokenStream,
+    item: proc_macro::TokenStream,
+) -> proc_macro::TokenStream {
+    let item = parse_macro_input!(item as Input);
+    let mut config: Config = parse_macro_input!(attr as Config);
+
+    config.supertraits = if let Some(supertraits) = config.supertraits.take() {
+        Some(parse_quote!(#supertraits + Sized))
+    } else {
+        Some(parse_quote!(Sized))
+    };
+
+    go(item, config)
+}
+
+fn go(item: Input, mut config: Config) -> proc_macro::TokenStream {
+    if let Some(vis) = item.vis {
+        if config.visibility != Visibility::Inherited {
+            abort!(
+                config.visibility.span(),
+                "Cannot set visibility on `#[ext]` and `impl` block"
+            );
+        }
+
+        config.visibility = vis;
+    }
+
+    let ItemImpl {
+        attrs,
+        unsafety,
+        generics,
+        trait_,
+        self_ty,
+        items,
+        // What is defaultness?
+        defaultness: _,
+        impl_token: _,
+        brace_token: _,
+    } = item.item_impl;
+
+    if let Some((_, path, _)) = trait_ {
+        abort!(path.span(), "Trait impls cannot be used for #[ext]");
+    }
+
+    let self_ty = parse_self_ty(&self_ty);
+
+    let ext_trait_name = config
+        .ext_trait_name
+        .unwrap_or_else(|| ext_trait_name(&self_ty));
+
+    let MethodsAndConsts {
+        trait_methods,
+        trait_consts,
+    } = extract_allowed_items(&items);
+
+    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
+
+    let visibility = &config.visibility;
+
+    let mut all_supertraits = Vec::<TypeParamBound>::new();
+
+    if let Some(supertraits_from_config) = config.supertraits {
+        all_supertraits.extend(supertraits_from_config);
+    }
+
+    let supertraits_quoted = if all_supertraits.is_empty() {
+        quote! {}
+    } else {
+        let supertraits_quoted = punctuated_from_iter::<_, _, Add>(all_supertraits);
+        quote! { : #supertraits_quoted }
+    };
+
+    let code = (quote! {
+        #[allow(non_camel_case_types)]
+        #(#attrs)*
+        #visibility
+        #unsafety
+        trait #ext_trait_name #impl_generics #supertraits_quoted #where_clause {
+            #(
+                #trait_consts
+            )*
+
+            #(
+                #[allow(
+                    patterns_in_fns_without_body,
+                    clippy::inline_fn_without_body,
+                    unused_attributes
+                )]
+                #trait_methods
+            )*
+        }
+
+        #(#attrs)*
+        impl #impl_generics #ext_trait_name #ty_generics for #self_ty #where_clause {
+            #(#items)*
+        }
+    })
+    .into();
+
+    code
+}
+
+#[derive(Debug, Clone)]
+enum ExtType<'a> {
+    Array(&'a TypeArray),
+    Group(&'a TypeGroup),
+    Never(&'a TypeNever),
+    Paren(&'a TypeParen),
+    Path(&'a TypePath),
+    Ptr(&'a TypePtr),
+    Reference(&'a TypeReference),
+    Slice(&'a TypeSlice),
+    Tuple(&'a TypeTuple),
+    BareFn(&'a TypeBareFn),
+    TraitObject(&'a TypeTraitObject),
+}
+
+#[allow(clippy::wildcard_in_or_patterns)]
+fn parse_self_ty(self_ty: &Type) -> ExtType {
+    match self_ty {
+        Type::Array(inner) => ExtType::Array(inner),
+        Type::Group(inner) => ExtType::Group(inner),
+        Type::Never(inner) => ExtType::Never(inner),
+        Type::Paren(inner) => ExtType::Paren(inner),
+        Type::Path(inner) => ExtType::Path(inner),
+        Type::Ptr(inner) => ExtType::Ptr(inner),
+        Type::Reference(inner) => ExtType::Reference(inner),
+        Type::Slice(inner) => ExtType::Slice(inner),
+        Type::Tuple(inner) => ExtType::Tuple(inner),
+        Type::BareFn(inner) => ExtType::BareFn(inner),
+        Type::TraitObject(inner) => ExtType::TraitObject(inner),
+
+        Type::ImplTrait(_) | Type::Infer(_) | Type::Macro(_) | Type::Verbatim(_) | _ => abort!(
+            self_ty.span(),
+            "#[ext] is not supported for this kind of type"
+        ),
+    }
+}
+
+impl<'a> From<&'a Type> for ExtType<'a> {
+    fn from(inner: &'a Type) -> ExtType<'a> {
+        parse_self_ty(inner)
+    }
+}
+
+impl<'a> ToTokens for ExtType<'a> {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        match self {
+            ExtType::Array(inner) => inner.to_tokens(tokens),
+            ExtType::Group(inner) => inner.to_tokens(tokens),
+            ExtType::Never(inner) => inner.to_tokens(tokens),
+            ExtType::Paren(inner) => inner.to_tokens(tokens),
+            ExtType::Path(inner) => inner.to_tokens(tokens),
+            ExtType::Ptr(inner) => inner.to_tokens(tokens),
+            ExtType::Reference(inner) => inner.to_tokens(tokens),
+            ExtType::Slice(inner) => inner.to_tokens(tokens),
+            ExtType::Tuple(inner) => inner.to_tokens(tokens),
+            ExtType::BareFn(inner) => inner.to_tokens(tokens),
+            ExtType::TraitObject(inner) => inner.to_tokens(tokens),
+        }
+    }
+}
+
+fn ext_trait_name(self_ty: &ExtType) -> Ident {
+    fn inner_self_ty(self_ty: &ExtType) -> Ident {
+        match self_ty {
+            ExtType::Path(inner) => find_and_combine_idents(inner),
+            ExtType::Reference(inner) => {
+                let name = inner_self_ty(&(&*inner.elem).into());
+                if inner.mutability.is_some() {
+                    format_ident!("RefMut{}", name)
+                } else {
+                    format_ident!("Ref{}", name)
+                }
+            }
+            ExtType::Array(inner) => {
+                let name = inner_self_ty(&(&*inner.elem).into());
+                format_ident!("ListOf{}", name)
+            }
+            ExtType::Group(inner) => {
+                let name = inner_self_ty(&(&*inner.elem).into());
+                format_ident!("Group{}", name)
+            }
+            ExtType::Paren(inner) => {
+                let name = inner_self_ty(&(&*inner.elem).into());
+                format_ident!("Paren{}", name)
+            }
+            ExtType::Ptr(inner) => {
+                let name = inner_self_ty(&(&*inner.elem).into());
+                format_ident!("PointerTo{}", name)
+            }
+            ExtType::Slice(inner) => {
+                let name = inner_self_ty(&(&*inner.elem).into());
+                format_ident!("SliceOf{}", name)
+            }
+            ExtType::Tuple(inner) => {
+                let mut name = format_ident!("TupleOf");
+                for elem in &inner.elems {
+                    name = format_ident!("{}{}", name, inner_self_ty(&elem.into()));
+                }
+                name
+            }
+            ExtType::Never(_) => format_ident!("Never"),
+            ExtType::BareFn(inner) => {
+                let mut name = format_ident!("BareFn");
+                for input in inner.inputs.iter() {
+                    name = format_ident!("{}{}", name, inner_self_ty(&(&input.ty).into()));
+                }
+                match &inner.output {
+                    syn::ReturnType::Default => {
+                        name = format_ident!("{}Unit", name);
+                    }
+                    syn::ReturnType::Type(_, ty) => {
+                        name = format_ident!("{}{}", name, inner_self_ty(&(&**ty).into()));
+                    }
+                }
+                name
+            }
+            ExtType::TraitObject(inner) => {
+                let mut name = format_ident!("TraitObject");
+                for bound in inner.bounds.iter() {
+                    match bound {
+                        TypeParamBound::Trait(bound) => {
+                            for segment in bound.path.segments.iter() {
+                                name = format_ident!("{}{}", name, segment.ident);
+                            }
+                        }
+                        TypeParamBound::Lifetime(lifetime) => {
+                            name = format_ident!("{}{}", name, lifetime.ident);
+                        }
+                    }
+                }
+                name
+            }
+        }
+    }
+
+    format_ident!("{}Ext", inner_self_ty(self_ty))
+}
+
+fn find_and_combine_idents(type_path: &TypePath) -> Ident {
+    use syn::visit::{self, Visit};
+
+    struct IdentVisitor<'a>(Vec<&'a Ident>);
+
+    impl<'a> Visit<'a> for IdentVisitor<'a> {
+        fn visit_ident(&mut self, i: &'a Ident) {
+            self.0.push(i);
+        }
+    }
+
+    let mut visitor = IdentVisitor(Vec::new());
+    visit::visit_type_path(&mut visitor, type_path);
+    let idents = visitor.0;
+
+    if idents.is_empty() {
+        abort!(type_path.span(), "Empty type path")
+    } else {
+        let start = &idents[0].span();
+        let combined_span = idents
+            .iter()
+            .map(|i| i.span())
+            .fold(*start, |a, b| a.join(b).unwrap_or(a));
+
+        let combined_name = idents.iter().map(|i| i.to_string()).collect::<String>();
+
+        Ident::new(&combined_name, combined_span)
+    }
+}
+
+#[derive(Debug, Default)]
+struct MethodsAndConsts {
+    trait_methods: Vec<TraitItemMethod>,
+    trait_consts: Vec<TraitItemConst>,
+}
+
+#[allow(clippy::wildcard_in_or_patterns)]
+fn extract_allowed_items(items: &[ImplItem]) -> MethodsAndConsts {
+    let mut acc = MethodsAndConsts::default();
+    for item in items {
+        match item {
+            ImplItem::Method(method) => acc.trait_methods.push(TraitItemMethod {
+                attrs: method.attrs.clone(),
+                sig: method.sig.clone(),
+                default: None,
+                semi_token: Some(Semi::default()),
+            }),
+            ImplItem::Const(const_) => acc.trait_consts.push(TraitItemConst {
+                attrs: const_.attrs.clone(),
+                const_token: Default::default(),
+                ident: const_.ident.clone(),
+                colon_token: Default::default(),
+                ty: const_.ty.clone(),
+                default: None,
+                semi_token: Default::default(),
+            }),
+            ImplItem::Type(_) => abort!(
+                item.span(),
+                "Associated types are not allowed in #[ext] impls"
+            ),
+            ImplItem::Macro(_) => abort!(item.span(), "Macros are not allowed in #[ext] impls"),
+            ImplItem::Verbatim(_) | _ => abort!(item.span(), "Not allowed in #[ext] impls"),
+        }
+    }
+    acc
+}
+
+#[derive(Debug)]
+struct Config {
+    ext_trait_name: Option<Ident>,
+    visibility: Visibility,
+    supertraits: Option<Punctuated<TypeParamBound, Add>>,
+}
+
+impl Parse for Config {
+    fn parse(input: ParseStream) -> parse::Result<Self> {
+        let mut config = Config::default();
+
+        if let Ok(visibility) = input.parse::<Visibility>() {
+            config.visibility = visibility;
+        }
+
+        input.parse::<Token![,]>().ok();
+
+        while !input.is_empty() {
+            let ident = input.parse::<Ident>()?;
+            input.parse::<Token![=]>()?;
+
+            match &*ident.to_string() {
+                "name" => {
+                    config.ext_trait_name = Some(input.parse()?);
+                }
+                "supertraits" => {
+                    config.supertraits =
+                        Some(Punctuated::<TypeParamBound, Add>::parse_terminated(input)?);
+                }
+                _ => abort!(ident.span(), "Unknown configuration name"),
+            }
+
+            input.parse::<Token![,]>().ok();
+        }
+
+        Ok(config)
+    }
+}
+
+impl Default for Config {
+    fn default() -> Self {
+        Self {
+            ext_trait_name: None,
+            visibility: Visibility::Inherited,
+            supertraits: None,
+        }
+    }
+}
+
+fn punctuated_from_iter<I, T, P>(i: I) -> Punctuated<T, P>
+where
+    P: Default,
+    I: IntoIterator<Item = T>,
+{
+    let mut iter = i.into_iter().peekable();
+    let mut acc = Punctuated::default();
+
+    while let Some(item) = iter.next() {
+        acc.push_value(item);
+
+        if iter.peek().is_some() {
+            acc.push_punct(P::default());
+        }
+    }
+
+    acc
+}
+
+#[cfg(test)]
+mod test {
+    #[allow(unused_imports)]
+    use super::*;
+
+    #[test]
+    fn test_ui() {
+        let t = trybuild::TestCases::new();
+        t.pass("tests/compile_pass/*.rs");
+        t.compile_fail("tests/compile_fail/*.rs");
+    }
+}
--- a/third_party/rust/extend/tests/compile_fail/double_vis.rs
+++ b/third_party/rust/extend/tests/compile_fail/double_vis.rs
@ -0,0 +1,14 @@
+mod a {
+    use extend::ext;
+
+    #[ext(pub(super))]
+    pub impl i32 {
+        fn foo() -> Foo {
+            Foo
+        }
+    }
+
+    pub struct Foo;
+}
+
+fn main() {}
--- a/third_party/rust/extend/tests/compile_fail/double_vis.stderr
+++ b/third_party/rust/extend/tests/compile_fail/double_vis.stderr
@ -0,0 +1,5 @@
+error: Cannot set visibility on `#[ext]` and `impl` block
+ --> $DIR/double_vis.rs:4:11
+  |
+4 |     #[ext(pub(super))]
+  |           ^^^
--- a/third_party/rust/extend/tests/compile_fail/supertraits_are_actually_included.rs
+++ b/third_party/rust/extend/tests/compile_fail/supertraits_are_actually_included.rs
@ -0,0 +1,14 @@
+use extend::ext;
+
+trait MyTrait {}
+
+#[ext(supertraits = MyTrait)]
+impl String {
+    fn my_len(&self) -> usize {
+        self.len()
+    }
+}
+
+fn main() {
+    assert_eq!(String::new().my_len(), 0);
+}
--- a/third_party/rust/extend/tests/compile_fail/supertraits_are_actually_included.stderr
+++ b/third_party/rust/extend/tests/compile_fail/supertraits_are_actually_included.stderr
@ -0,0 +1,10 @@
+error[E0277]: the trait bound `String: MyTrait` is not satisfied
+ --> $DIR/supertraits_are_actually_included.rs:6:6
+  |
+5 | #[ext(supertraits = MyTrait)]
+  |                     ------- required by this bound in `StringExt`
+6 | impl String {
+  |      ^^^^^^
+  |      |
+  |      the trait `MyTrait` is not implemented for `String`
+  |      required by a bound in this
--- a/third_party/rust/extend/tests/compile_pass/associated_constants.rs
+++ b/third_party/rust/extend/tests/compile_pass/associated_constants.rs
@ -0,0 +1,10 @@
+use extend::ext;
+
+#[ext]
+impl Option<String> {
+    const FOO: usize = 1;
+}
+
+fn main() {
+    assert_eq!(Option::<String>::FOO, 1);
+}
--- a/third_party/rust/extend/tests/compile_pass/async_trait.rs
+++ b/third_party/rust/extend/tests/compile_pass/async_trait.rs
@ -0,0 +1,25 @@
+use extend::ext;
+use async_trait::async_trait;
+
+#[ext]
+#[async_trait]
+impl String {
+    async fn foo() -> usize {
+        1
+    }
+}
+
+#[ext]
+#[async_trait]
+pub impl i32 {
+    async fn bar() -> usize {
+        1
+    }
+}
+
+async fn foo() {
+    let _: usize = String::foo().await;
+    let _: usize = i32::bar().await;
+}
+
+fn main() {}
--- a/third_party/rust/extend/tests/compile_pass/changing_extension_trait_name.rs
+++ b/third_party/rust/extend/tests/compile_pass/changing_extension_trait_name.rs
@ -0,0 +1,10 @@
+use extend::ext;
+
+#[ext(name = Foo)]
+impl i32 {
+    fn foo() {}
+}
+
+fn main() {
+    <i32 as Foo>::foo();
+}
--- a/third_party/rust/extend/tests/compile_pass/complex_trait_name.rs
+++ b/third_party/rust/extend/tests/compile_pass/complex_trait_name.rs
@ -0,0 +1,16 @@
+mod foo {
+    use extend::ext;
+
+    #[ext(pub)]
+    impl<T1, T2, T3> (T1, T2, T3) {
+        fn size(&self) -> usize {
+            3
+        }
+    }
+}
+
+fn main() {
+    use foo::TupleOfT1T2T3Ext;
+
+    assert_eq!(3, (0, 0, 0).size());
+}
--- a/third_party/rust/extend/tests/compile_pass/double_ext_on_same_type.rs
+++ b/third_party/rust/extend/tests/compile_pass/double_ext_on_same_type.rs
@ -0,0 +1,17 @@
+use extend::ext;
+
+#[ext]
+impl Option<usize> {
+    fn foo() -> usize {
+        1
+    }
+}
+
+#[ext]
+impl Option<i32> {
+    fn bar() -> i32 {
+        1
+    }
+}
+
+fn main() {}
--- a/third_party/rust/extend/tests/compile_pass/extension_on_complex_types.rs
+++ b/third_party/rust/extend/tests/compile_pass/extension_on_complex_types.rs
@ -0,0 +1,58 @@
+use extend::ext;
+
+#[ext]
+impl<'a> &'a str {
+    fn foo(self) {}
+}
+
+#[ext]
+impl<T> [T; 3] {
+    fn foo(self) {}
+}
+
+#[ext]
+impl *const i32 {
+    fn foo(self) {}
+}
+
+#[ext]
+impl<T> [T] {
+    fn foo(&self) {}
+}
+
+#[ext]
+impl<'a, T> &'a [T] {
+    fn foo(self) {}
+}
+
+#[ext]
+impl (i32, i64) {
+    fn foo(self) {}
+}
+
+#[ext]
+impl fn(i32) -> bool {
+    fn foo(self) {}
+}
+
+fn bare_fn(_: i32) -> bool {
+    false
+}
+
+#[ext]
+impl dyn Send + Sync + 'static {}
+
+fn main() {
+    "".foo();
+
+    [1, 2, 3].foo();
+
+    let ptr: *const i32 = &123;
+    ptr.foo();
+
+    &[1, 2, 3].foo();
+
+    (1i32, 1i64).foo();
+
+    (bare_fn as fn(i32) -> bool).foo();
+}
--- a/third_party/rust/extend/tests/compile_pass/generics.rs
+++ b/third_party/rust/extend/tests/compile_pass/generics.rs
@ -0,0 +1,15 @@
+use extend::ext;
+
+#[ext]
+impl<'a, T: Clone> Vec<&'a T>
+where
+    T: 'a + Copy,
+{
+    fn size(&self) -> usize {
+        self.len()
+    }
+}
+
+fn main() {
+    assert_eq!(3, vec![&1, &2, &3].size());
+}
--- a/third_party/rust/extend/tests/compile_pass/hello_world.rs
+++ b/third_party/rust/extend/tests/compile_pass/hello_world.rs
@ -0,0 +1,20 @@
+use extend::ext;
+
+#[ext]
+impl i32 {
+    fn add_one(&self) -> Self {
+        self + 1
+    }
+
+    fn foo() -> MyType {
+        MyType
+    }
+}
+
+#[derive(Debug, Eq, PartialEq)]
+struct MyType;
+
+fn main() {
+    assert_eq!(i32::foo(), MyType);
+    assert_eq!(1.add_one(), 2);
+}
--- a/third_party/rust/extend/tests/compile_pass/issue_2.rs
+++ b/third_party/rust/extend/tests/compile_pass/issue_2.rs
@ -0,0 +1,33 @@
+#![allow(unused_variables)]
+
+use extend::ext;
+use std::iter::FromIterator;
+
+#[ext]
+impl<T, K, F, C> C
+where
+    C: IntoIterator<Item = T>,
+    K: Eq,
+    F: Fn(&T) -> K,
+{
+    fn group_by<Out>(self, f: F) -> Out
+    where
+        Out: FromIterator<(K, Vec<T>)>,
+    {
+        todo!()
+    }
+
+    fn group_by_and_map_values<Out, G, T2>(self, f: F, g: G) -> Out
+    where
+        G: Fn(T) -> T2 + Copy,
+        Out: FromIterator<(K, Vec<T2>)>,
+    {
+        todo!()
+    }
+
+    fn group_by_and_return_groups(self, f: F) -> Vec<Vec<T>> {
+        todo!()
+    }
+}
+
+fn main() {}
--- a/third_party/rust/extend/tests/compile_pass/more_than_one_extension.rs
+++ b/third_party/rust/extend/tests/compile_pass/more_than_one_extension.rs
@ -0,0 +1,13 @@
+use extend::ext;
+
+#[ext]
+impl i32 {
+    fn foo() {}
+}
+
+#[ext]
+impl i64 {
+    fn bar() {}
+}
+
+fn main() {}
--- a/third_party/rust/extend/tests/compile_pass/multiple_config.rs
+++ b/third_party/rust/extend/tests/compile_pass/multiple_config.rs
@ -0,0 +1,13 @@
+use extend::ext;
+
+#[ext(pub(crate), name = Foo)]
+impl i32 {
+    fn foo() {}
+}
+
+#[ext(pub, name = Bar)]
+impl i64 {
+    fn foo() {}
+}
+
+fn main() {}
--- a/third_party/rust/extend/tests/compile_pass/multiple_generic_params.rs
+++ b/third_party/rust/extend/tests/compile_pass/multiple_generic_params.rs
@ -0,0 +1,11 @@
+use extend::ext;
+use std::marker::PhantomData;
+
+struct Foo<T>(PhantomData<T>);
+
+#[ext]
+impl<T, K> T {
+    fn some_method(&self, _: Foo<K>) {}
+}
+
+fn main() {}
--- a/third_party/rust/extend/tests/compile_pass/pub_impl.rs
+++ b/third_party/rust/extend/tests/compile_pass/pub_impl.rs
@ -0,0 +1,15 @@
+mod a {
+    use extend::ext;
+
+    #[ext]
+    pub impl i32 {
+        fn foo() -> Foo { Foo }
+    }
+
+    pub struct Foo;
+}
+
+fn main() {
+    use a::i32Ext;
+    i32::foo();
+}
--- a/third_party/rust/extend/tests/compile_pass/ref_and_ref_mut.rs
+++ b/third_party/rust/extend/tests/compile_pass/ref_and_ref_mut.rs
@ -0,0 +1,13 @@
+use extend::ext;
+
+#[ext]
+impl &i32 {
+    fn foo() {}
+}
+
+#[ext]
+impl &mut i32 {
+    fn bar() {}
+}
+
+fn main() {}
--- a/third_party/rust/extend/tests/compile_pass/sized.rs
+++ b/third_party/rust/extend/tests/compile_pass/sized.rs
@ -0,0 +1,36 @@
+use extend::ext_sized;
+
+#[ext_sized(name = One)]
+impl i32 {
+    fn requires_sized(self) -> Option<Self> {
+        Some(self)
+    }
+}
+
+#[ext_sized(name = Two, supertraits = Default)]
+impl i32 {
+    fn with_another_supertrait(self) -> Option<Self> {
+        Some(self)
+    }
+}
+
+#[ext_sized(name = Three, supertraits = Default + Clone + Copy)]
+impl i32 {
+    fn multiple_supertraits(self) -> Option<Self> {
+        Some(self)
+    }
+}
+
+#[ext_sized(name = Four, supertraits = Sized)]
+impl i32 {
+    fn already_sized(self) -> Option<Self> {
+        Some(self)
+    }
+}
+
+fn main() {
+    1.requires_sized();
+    1.with_another_supertrait();
+    1.multiple_supertraits();
+    1.already_sized();
+}
--- a/third_party/rust/extend/tests/compile_pass/super_trait.rs
+++ b/third_party/rust/extend/tests/compile_pass/super_trait.rs
@ -0,0 +1,16 @@
+use extend::ext;
+
+trait MyTrait {}
+
+impl MyTrait for String {}
+
+#[ext(supertraits = Default + Clone + MyTrait)]
+impl String {
+    fn my_len(&self) -> usize {
+        self.len()
+    }
+}
+
+fn main() {
+    assert_eq!(String::new().my_len(), 0);
+}
--- a/third_party/rust/extend/tests/compile_pass/visibility_config.rs
+++ b/third_party/rust/extend/tests/compile_pass/visibility_config.rs
@ -0,0 +1,15 @@
+mod a {
+    use extend::ext;
+
+    #[ext(pub)]
+    impl i32 {
+        fn foo() -> Foo { Foo }
+    }
+
+    pub struct Foo;
+}
+
+fn main() {
+    use a::i32Ext;
+    i32::foo();
+}
--- a/third_party/rust/uniffi-example-arithmetic/.cargo-checksum.json
+++ b/third_party/rust/uniffi-example-arithmetic/.cargo-checksum.json
@ -0,0 +1 @@
+{"files":{"Cargo.toml":"90295a750f9c69ee799ac767d56eaee2c3218df7964f11c885b6910a31d07a25","build.rs":"05089b35ac197b5ff83c75872a70df023834141831d0c2051faa35b4c9df55ba","src/arithmetic.udl":"8554c6907ece627645f6b896f71430e5412bf19b0ac6becf63eb9a69868d0f7a","src/lib.rs":"92ebd9fc4d3403ab1960d2d8520c1217971147ea3aebff89228a61fcbb8b2af3","tests/bindings/test_arithmetic.kts":"e0e9347755db4e18f70b1b74c2d5a4aa328373015090ed959b46d65c2a205d92","tests/bindings/test_arithmetic.py":"3e41d69e21e96a6830197c760f3b7bddd754edc0c5515b7bd33b79cccb10f941","tests/bindings/test_arithmetic.rb":"ea0fdce0a4c7b557b427db77521da05240cd6e87d60a128ac2307fab3bbbc76d","tests/bindings/test_arithmetic.swift":"455b87d95fc690af9c35f9e43676e9c855dedddd2fc1c9e1cbaa6a02835c2d4c","tests/test_generated_bindings.rs":"09b0e79c7e769bcf5f3a8b768247a05892d408d48e0295f6737de3c8dab28479","uniffi.toml":"ad149df611a6e3a853a029d90a88a694660f6a4ebe18dcb5f9f503819761dacd"},"package":null}
--- a/third_party/rust/uniffi-example-arithmetic/Cargo.toml
+++ b/third_party/rust/uniffi-example-arithmetic/Cargo.toml
@ -0,0 +1,19 @@
+[package]
+name = "uniffi-example-arithmetic"
+edition = "2021"
+version = "0.18.0"
+authors = ["Firefox Sync Team <sync-team@mozilla.com>"]
+license = "MPL-2.0"
+publish = false
+
+[lib]
+crate-type = ["lib", "cdylib"]
+name = "arithmetical"
+
+[dependencies]
+uniffi_macros = {path = "../../uniffi_macros"}
+uniffi = {path = "../../uniffi", features=["builtin-bindgen"]}
+thiserror = "1.0"
+
+[build-dependencies]
+uniffi_build = {path = "../../uniffi_build", features=["builtin-bindgen"]}
--- a/third_party/rust/uniffi-example-arithmetic/build.rs
+++ b/third_party/rust/uniffi-example-arithmetic/build.rs
@ -0,0 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+fn main() {
+    uniffi_build::generate_scaffolding("./src/arithmetic.udl").unwrap();
+}
--- a/third_party/rust/uniffi-example-arithmetic/src/arithmetic.udl
+++ b/third_party/rust/uniffi-example-arithmetic/src/arithmetic.udl
@ -0,0 +1,16 @@
+[Error]
+enum ArithmeticError {
+  "IntegerOverflow",
+};
+
+namespace arithmetic {
+  [Throws=ArithmeticError]
+  u64 add(u64 a, u64 b);
+
+  [Throws=ArithmeticError]
+  u64 sub(u64 a, u64 b);
+
+  u64 div(u64 dividend, u64 divisor);
+
+  boolean equal(u64 a, u64 b);
+};
--- a/third_party/rust/uniffi-example-arithmetic/src/lib.rs
+++ b/third_party/rust/uniffi-example-arithmetic/src/lib.rs
@ -0,0 +1,34 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#[derive(Debug, thiserror::Error)]
+pub enum ArithmeticError {
+    #[error("Integer overflow on an operation with {a} and {b}")]
+    IntegerOverflow { a: u64, b: u64 },
+}
+
+fn add(a: u64, b: u64) -> Result<u64> {
+    a.checked_add(b)
+        .ok_or(ArithmeticError::IntegerOverflow { a, b })
+}
+
+fn sub(a: u64, b: u64) -> Result<u64> {
+    a.checked_sub(b)
+        .ok_or(ArithmeticError::IntegerOverflow { a, b })
+}
+
+fn div(dividend: u64, divisor: u64) -> u64 {
+    if divisor == 0 {
+        panic!("Can't divide by zero");
+    }
+    dividend / divisor
+}
+
+fn equal(a: u64, b: u64) -> bool {
+    a == b
+}
+
+type Result<T, E = ArithmeticError> = std::result::Result<T, E>;
+
+uniffi_macros::include_scaffolding!("arithmetic");
--- a/third_party/rust/uniffi-example-arithmetic/tests/bindings/test_arithmetic.kts
+++ b/third_party/rust/uniffi-example-arithmetic/tests/bindings/test_arithmetic.kts
@ -0,0 +1,29 @@
+import org.mozilla.uniffi.example.arithmetic.*;
+
+assert(add(2u, 4u) == 6uL)
+assert(add(4u, 8u) == 12uL)
+
+try {
+    sub(0u, 2u)
+    throw RuntimeException("Should have thrown a IntegerOverflow exception!")
+} catch (e: ArithmeticException) {
+    // It's okay!
+}
+
+assert(sub(4u, 2u) == 2uL)
+assert(sub(8u, 4u) == 4uL)
+
+assert(div(8u, 4u) == 2uL)
+
+try {
+    div(8u, 0u)
+    throw RuntimeException("Should have panicked when dividing by zero")
+} catch (e: InternalException) {
+    // It's okay!
+}
+
+assert(equal(2u, 2uL))
+assert(equal(4u, 4uL))
+
+assert(!equal(2u, 4uL))
+assert(!equal(4u, 8uL))
--- a/third_party/rust/uniffi-example-arithmetic/tests/bindings/test_arithmetic.py
+++ b/third_party/rust/uniffi-example-arithmetic/tests/bindings/test_arithmetic.py
@ -0,0 +1,37 @@
+from arithmetic import *
+
+try:
+    add(18446744073709551615, 1)
+    assert(not("Should have thrown a IntegerOverflow exception!"))
+except ArithmeticError.IntegerOverflow:
+    # It's okay!
+    pass
+
+assert add(2, 4) == 6
+assert add(4, 8) == 12
+
+try:
+    sub(0, 1)
+    assert(not("Should have thrown a IntegerOverflow exception!"))
+except ArithmeticError.IntegerOverflow:
+    # It's okay!
+    pass
+
+assert sub(4, 2) == 2
+assert sub(8, 4) == 4
+
+assert div(8, 4) == 2
+
+try:
+    div(8, 0)
+except InternalError:
+    # It's okay!
+    pass
+else:
+    assert(not("Should have panicked when dividing by zero"))
+
+assert equal(2, 2)
+assert equal(4, 4)
+
+assert not equal(2, 4)
+assert not equal(4, 8)
--- a/third_party/rust/uniffi-example-arithmetic/tests/bindings/test_arithmetic.rb
+++ b/third_party/rust/uniffi-example-arithmetic/tests/bindings/test_arithmetic.rb
@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require 'test/unit'
+require 'arithmetic'
+
+include Test::Unit::Assertions
+
+assert_raise Arithmetic::ArithmeticError::IntegerOverflow do
+  Arithmetic.add 18_446_744_073_709_551_615, 1
+end
+
+assert_equal Arithmetic.add(2, 4), 6
+assert_equal Arithmetic.add(4, 8), 12
+
+assert_raise Arithmetic::ArithmeticError::IntegerOverflow do
+  Arithmetic.sub 0, 1
+end
+
+assert_equal Arithmetic.sub(4, 2), 2
+assert_equal Arithmetic.sub(8, 4), 4
+assert_equal Arithmetic.div(8, 4), 2
+
+assert_raise Arithmetic::InternalError do
+  Arithmetic.div 8, 0
+end
+
+assert Arithmetic.equal(2, 2)
+assert Arithmetic.equal(4, 4)
+
+assert !Arithmetic.equal(2, 4)
+assert !Arithmetic.equal(4, 8)
--- a/third_party/rust/uniffi-example-arithmetic/tests/bindings/test_arithmetic.swift
+++ b/third_party/rust/uniffi-example-arithmetic/tests/bindings/test_arithmetic.swift
@ -0,0 +1,32 @@
+import arithmetic
+
+do {
+    let _ = try add(a: 18446744073709551615, b: 1)
+    fatalError("Should have thrown a IntegerOverflow exception!")
+} catch ArithmeticError.IntegerOverflow {
+    // It's okay!
+}
+
+assert(try! add(a: 2, b: 4) == 6, "add work")
+assert(try! add(a: 4, b: 8) == 12, "add work")
+
+do {
+    let _ = try sub(a: 0, b: 1)
+    fatalError("Should have thrown a IntegerOverflow exception!")
+} catch ArithmeticError.IntegerOverflow {
+    // It's okay!
+}
+
+assert(try! sub(a: 4, b: 2) == 2, "sub work")
+assert(try! sub(a: 8, b: 4) == 4, "sub work")
+
+assert(div(dividend: 8, divisor: 4) == 2, "div works")
+
+// We can't test panicking in Swift because we force unwrap the error in
+// `div`, which we can't catch.
+
+assert(equal(a: 2, b: 2), "equal works")
+assert(equal(a: 4, b: 4), "equal works")
+
+assert(!equal(a: 2, b: 4), "non-equal works")
+assert(!equal(a: 4, b: 8), "non-equal works")
--- a/third_party/rust/uniffi-example-arithmetic/tests/test_generated_bindings.rs
+++ b/third_party/rust/uniffi-example-arithmetic/tests/test_generated_bindings.rs
@ -0,0 +1,9 @@
+uniffi_macros::build_foreign_language_testcases!(
+    ["src/arithmetic.udl",],
+    [
+        "tests/bindings/test_arithmetic.rb",
+        "tests/bindings/test_arithmetic.py",
+        "tests/bindings/test_arithmetic.kts",
+        "tests/bindings/test_arithmetic.swift",
+    ]
+);
--- a/third_party/rust/uniffi-example-arithmetic/uniffi.toml
+++ b/third_party/rust/uniffi-example-arithmetic/uniffi.toml
@ -0,0 +1,12 @@
+[bindings.kotlin]
+package_name = "org.mozilla.uniffi.example.arithmetic"
+cdylib_name = "arithmetical"
+
+[bindings.python]
+cdylib_name = "arithmetical"
+
+[bindings.ruby]
+cdylib_name = "arithmetical"
+
+[bindings.swift]
+cdylib_name = "arithmetical"
--- a/third_party/rust/uniffi-example-geometry/.cargo-checksum.json
+++ b/third_party/rust/uniffi-example-geometry/.cargo-checksum.json
@ -0,0 +1 @@
+{"files":{"Cargo.toml":"15bbf6e8c0d438e7f776dfdcf8da5fefb41e4b5bacafe97d1fcb10389d07ed9b","build.rs":"94ca4e70e538a2159cb77157c227d487973756373c4b27ea5cea05a6698cb60b","src/geometry.udl":"7da7a6ec080c7117ec3c25206e23f9ed436e60b1a26fba34f991547680443550","src/lib.rs":"be9c624f691a8d1ebe3be6dbbcde44033759b8321a3a298453018dd69b9c14c7","tests/bindings/test_geometry.kts":"e537185e3c699df1c0468525700e8a38f9a504b2a663c38442146b951e38e9a7","tests/bindings/test_geometry.py":"3ea483b8a4fbe13aefa6641177ae149f75f734bc32bf0da533b97c1abf3dc317","tests/bindings/test_geometry.rb":"17c2fe8a7b477419a6646983dd88f1b07a0304b58a568c03e9bfa640d5b2df5c","tests/bindings/test_geometry.swift":"a61fec6bfe16020809e20e4da372748c24366767138c5672a0bfff85c4b62d78","tests/test_generated_bindings.rs":"8ba67396105b96cc554f78078c7a8c6e8ce86ecc868d97a069a5f60fd87c1a36","uniffi.toml":"5b28f45d3c2581a52cf886a502f034778a002815b66994e5da2081a5c9f5284b"},"package":null}
--- a/third_party/rust/uniffi-example-geometry/Cargo.toml
+++ b/third_party/rust/uniffi-example-geometry/Cargo.toml
@ -0,0 +1,18 @@
+[package]
+name = "uniffi-example-geometry"
+edition = "2021"
+version = "0.18.0"
+authors = ["Firefox Sync Team <sync-team@mozilla.com>"]
+license = "MPL-2.0"
+publish = false
+
+[lib]
+crate-type = ["lib", "cdylib"]
+name = "uniffi_geometry"
+
+[dependencies]
+uniffi_macros = {path = "../../uniffi_macros"}
+uniffi = {path = "../../uniffi", features=["builtin-bindgen"]}
+
+[build-dependencies]
+uniffi_build = {path = "../../uniffi_build", features=["builtin-bindgen"]}
--- a/third_party/rust/uniffi-example-geometry/build.rs
+++ b/third_party/rust/uniffi-example-geometry/build.rs
@ -0,0 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+fn main() {
+    uniffi_build::generate_scaffolding("./src/geometry.udl").unwrap();
+}
--- a/third_party/rust/uniffi-example-geometry/src/geometry.udl
+++ b/third_party/rust/uniffi-example-geometry/src/geometry.udl
@ -0,0 +1,15 @@
+
+namespace geometry {
+  double gradient(Line ln);
+  Point? intersection(Line ln1, Line ln2);
+};
+
+dictionary Point {
+  double coord_x;
+  double coord_y;
+};
+
+dictionary Line {
+  Point start;
+  Point end;
+};
--- a/third_party/rust/uniffi-example-geometry/src/lib.rs
+++ b/third_party/rust/uniffi-example-geometry/src/lib.rs
@ -0,0 +1,47 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// https://rust-lang.github.io/rust-clippy/master/index.html#float_cmp
+// Silence, clippy!
+const EPSILON: f64 = 0.0001f64;
+
+#[derive(Debug, Clone)]
+pub struct Point {
+    coord_x: f64,
+    coord_y: f64,
+}
+
+#[derive(Debug, Clone)]
+pub struct Line {
+    start: Point,
+    end: Point,
+}
+
+pub fn gradient(ln: Line) -> f64 {
+    let rise = ln.end.coord_y - ln.start.coord_y;
+    let run = ln.end.coord_x - ln.start.coord_x;
+    rise / run
+}
+
+pub fn intersection(ln1: Line, ln2: Line) -> Option<Point> {
+    // TODO: yuck, should be able to take &Line as argument here
+    // and have rust figure it out with a bunch of annotations...
+    let g1 = gradient(ln1.clone());
+    let z1 = ln1.start.coord_y - g1 * ln1.start.coord_x;
+    let g2 = gradient(ln2.clone());
+    let z2 = ln2.start.coord_y - g2 * ln2.start.coord_x;
+    // Parallel lines do not intersect.
+    if (g1 - g2).abs() < EPSILON {
+        return None;
+    }
+    // Otherwise, they intersect at this fancy calculation that
+    // I found on wikipedia.
+    let x = (z2 - z1) / (g1 - g2);
+    Some(Point {
+        coord_x: x,
+        coord_y: g1 * x + z1,
+    })
+}
+
+include!(concat!(env!("OUT_DIR"), "/geometry.uniffi.rs"));
--- a/third_party/rust/uniffi-example-geometry/tests/bindings/test_geometry.kts
+++ b/third_party/rust/uniffi-example-geometry/tests/bindings/test_geometry.kts
@ -0,0 +1,10 @@
+import uniffi.geometry.*;
+
+val ln1 = Line(Point(0.0,0.0), Point(1.0,2.0))
+val ln2 = Line(Point(1.0,1.0), Point(2.0,2.0))
+
+assert( gradient(ln1) == 2.0 )
+assert( gradient(ln2) == 1.0 )
+
+assert( intersection(ln1, ln2) == Point(0.0, 0.0) )
+assert( intersection(ln1, ln1) == null )
--- a/third_party/rust/uniffi-example-geometry/tests/bindings/test_geometry.py
+++ b/third_party/rust/uniffi-example-geometry/tests/bindings/test_geometry.py
@ -0,0 +1,10 @@
+from geometry import *
+
+ln1 = Line(Point(0,0), Point(1,2))
+ln2 = Line(Point(1,1), Point(2,2))
+
+assert gradient(ln1) == 2
+assert gradient(ln2) == 1
+
+assert intersection(ln1, ln2) == Point(0, 0)
+assert intersection(ln1, ln1) is None
--- a/third_party/rust/uniffi-example-geometry/tests/bindings/test_geometry.rb
+++ b/third_party/rust/uniffi-example-geometry/tests/bindings/test_geometry.rb
@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+require 'test/unit'
+require 'geometry'
+
+include Test::Unit::Assertions
+include Geometry
+
+ln1 = Line.new(Point.new(0.0, 0.0), Point.new(1.0, 2.0))
+ln2 = Line.new(Point.new(1.0, 1.0), Point.new(2.0, 2.0))
+
+assert_equal Geometry.gradient(ln1), 2
+assert_equal Geometry.gradient(ln2), 1
+
+assert_equal Geometry.intersection(ln1, ln2), Point.new(0, 0)
+assert Geometry.intersection(ln1, ln1).nil?
--- a/third_party/rust/uniffi-example-geometry/tests/bindings/test_geometry.swift
+++ b/third_party/rust/uniffi-example-geometry/tests/bindings/test_geometry.swift
@ -0,0 +1,10 @@
+import geometry
+
+let ln1 = Line(start: Point(coordX: 0, coordY: 0), end: Point(coordX: 1, coordY: 2))
+let ln2 = Line(start: Point(coordX: 1, coordY: 1), end: Point(coordX: 2, coordY: 2))
+
+assert(gradient(ln: ln1) == 2.0)
+assert(gradient(ln: ln2) == 1.0)
+
+assert(intersection(ln1: ln1, ln2: ln2) == Point(coordX: 0, coordY: 0))
+assert(intersection(ln1: ln1, ln2: ln1) == nil)
--- a/third_party/rust/uniffi-example-geometry/tests/test_generated_bindings.rs
+++ b/third_party/rust/uniffi-example-geometry/tests/test_generated_bindings.rs
@ -0,0 +1,9 @@
+uniffi_macros::build_foreign_language_testcases!(
+    ["src/geometry.udl",],
+    [
+        "tests/bindings/test_geometry.py",
+        "tests/bindings/test_geometry.rb",
+        "tests/bindings/test_geometry.kts",
+        "tests/bindings/test_geometry.swift",
+    ]
+);
--- a/third_party/rust/uniffi-example-geometry/uniffi.toml
+++ b/third_party/rust/uniffi-example-geometry/uniffi.toml
@ -0,0 +1 @@
+[bindings.swift]
--- a/third_party/rust/uniffi-example-rondpoint/.cargo-checksum.json
+++ b/third_party/rust/uniffi-example-rondpoint/.cargo-checksum.json
@ -0,0 +1 @@
+{"files":{"Cargo.toml":"e26e9e2826e89bf73aed693d2cea2aa1e2ce3d32cb0f03136cc29352f851295c","build.rs":"c48df8045c6cf73a8f3b8e93af7878f4ce1e7baa11f0688d661405f339df4ba4","src/lib.rs":"70b9ab1fb944d3af1ce53ce097caf52d1ebbf0e18be1e70bf57e5cec96e76502","src/rondpoint.udl":"ca4d8720758608b06ffd5f81bfc73881fbd0693a7a5b21bfe61a4557ea052048","tests/bindings/test_rondpoint.kts":"87b3d507f4260aae4e4711263c13b7158b9a814cb97bf5219d1451f348cd7372","tests/bindings/test_rondpoint.py":"d618274170af767f8a5614a2565ea698b26ea3e1a222d5c110e7b2d00763e73b","tests/bindings/test_rondpoint.rb":"9cc49df311823d6caedbe7b05ff8c4da6329063c2ce16810192aaaa7edcdf5f5","tests/bindings/test_rondpoint.swift":"471cf430be35dcdc19b3166adbc08561e0bd939931edc37da974e0fd16a49331","tests/test_generated_bindings.rs":"5843b2c9d6b86b35ab932349d278d9f281493880a1395e0b7566e297fad36c7d"},"package":null}
--- a/third_party/rust/uniffi-example-rondpoint/Cargo.toml
+++ b/third_party/rust/uniffi-example-rondpoint/Cargo.toml
@ -0,0 +1,18 @@
+[package]
+name = "uniffi-example-rondpoint"
+edition = "2021"
+version = "0.18.0"
+authors = ["Firefox Sync Team <sync-team@mozilla.com>"]
+license = "MPL-2.0"
+publish = false
+
+[lib]
+crate-type = ["lib", "cdylib"]
+name = "uniffi_rondpoint"
+
+[dependencies]
+uniffi_macros = {path = "../../uniffi_macros"}
+uniffi = {path = "../../uniffi", features=["builtin-bindgen"]}
+
+[build-dependencies]
+uniffi_build = {path = "../../uniffi_build", features=["builtin-bindgen"]}
--- a/third_party/rust/uniffi-example-rondpoint/build.rs
+++ b/third_party/rust/uniffi-example-rondpoint/build.rs
@ -0,0 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+fn main() {
+    uniffi_build::generate_scaffolding("./src/rondpoint.udl").unwrap();
+}
--- a/third_party/rust/uniffi-example-rondpoint/src/lib.rs
+++ b/third_party/rust/uniffi-example-rondpoint/src/lib.rs
@ -0,0 +1,293 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use std::collections::HashMap;
+
+#[derive(Debug, Clone)]
+pub struct Dictionnaire {
+    un: Enumeration,
+    deux: bool,
+    petit_nombre: u8,
+    gros_nombre: u64,
+}
+
+#[derive(Debug, Clone)]
+pub struct DictionnaireNombres {
+    petit_nombre: u8,
+    court_nombre: u16,
+    nombre_simple: u32,
+    gros_nombre: u64,
+}
+
+#[derive(Debug, Clone)]
+pub struct DictionnaireNombresSignes {
+    petit_nombre: i8,
+    court_nombre: i16,
+    nombre_simple: i32,
+    gros_nombre: i64,
+}
+
+#[derive(Debug, Clone)]
+pub enum Enumeration {
+    Un,
+    Deux,
+    Trois,
+}
+
+#[derive(Debug, Clone)]
+pub enum EnumerationAvecDonnees {
+    Zero,
+    Un { premier: u32 },
+    Deux { premier: u32, second: String },
+}
+
+#[allow(non_camel_case_types)]
+#[allow(non_snake_case)]
+pub struct minusculeMAJUSCULEDict {
+    minusculeMAJUSCULEField: bool,
+}
+
+#[allow(non_camel_case_types)]
+pub enum minusculeMAJUSCULEEnum {
+    minusculeMAJUSCULEVariant,
+}
+
+fn copie_enumeration(e: Enumeration) -> Enumeration {
+    e
+}
+
+fn copie_enumerations(e: Vec<Enumeration>) -> Vec<Enumeration> {
+    e
+}
+
+fn copie_carte(
+    e: HashMap<String, EnumerationAvecDonnees>,
+) -> HashMap<String, EnumerationAvecDonnees> {
+    e
+}
+
+fn copie_dictionnaire(d: Dictionnaire) -> Dictionnaire {
+    d
+}
+
+fn switcheroo(b: bool) -> bool {
+    !b
+}
+
+// Test that values can traverse both ways across the FFI.
+// Even if roundtripping works, it's possible we have
+// symmetrical errors that cancel each other out.
+#[derive(Debug, Clone)]
+struct Retourneur;
+impl Retourneur {
+    fn new() -> Self {
+        Retourneur
+    }
+    fn identique_i8(&self, value: i8) -> i8 {
+        value
+    }
+    fn identique_u8(&self, value: u8) -> u8 {
+        value
+    }
+    fn identique_i16(&self, value: i16) -> i16 {
+        value
+    }
+    fn identique_u16(&self, value: u16) -> u16 {
+        value
+    }
+    fn identique_i32(&self, value: i32) -> i32 {
+        value
+    }
+    fn identique_u32(&self, value: u32) -> u32 {
+        value
+    }
+    fn identique_i64(&self, value: i64) -> i64 {
+        value
+    }
+    fn identique_u64(&self, value: u64) -> u64 {
+        value
+    }
+    fn identique_float(&self, value: f32) -> f32 {
+        value
+    }
+    fn identique_double(&self, value: f64) -> f64 {
+        value
+    }
+    fn identique_boolean(&self, value: bool) -> bool {
+        value
+    }
+    fn identique_string(&self, value: String) -> String {
+        value
+    }
+    fn identique_nombres_signes(
+        &self,
+        value: DictionnaireNombresSignes,
+    ) -> DictionnaireNombresSignes {
+        value
+    }
+    fn identique_nombres(&self, value: DictionnaireNombres) -> DictionnaireNombres {
+        value
+    }
+    fn identique_optionneur_dictionnaire(
+        &self,
+        value: OptionneurDictionnaire,
+    ) -> OptionneurDictionnaire {
+        value
+    }
+}
+
+#[derive(Debug, Clone)]
+struct Stringifier;
+
+#[allow(dead_code)]
+impl Stringifier {
+    fn new() -> Self {
+        Stringifier
+    }
+    fn to_string_i8(&self, value: i8) -> String {
+        value.to_string()
+    }
+    fn to_string_u8(&self, value: u8) -> String {
+        value.to_string()
+    }
+    fn to_string_i16(&self, value: i16) -> String {
+        value.to_string()
+    }
+    fn to_string_u16(&self, value: u16) -> String {
+        value.to_string()
+    }
+    fn to_string_i32(&self, value: i32) -> String {
+        value.to_string()
+    }
+    fn to_string_u32(&self, value: u32) -> String {
+        value.to_string()
+    }
+    fn to_string_i64(&self, value: i64) -> String {
+        value.to_string()
+    }
+    fn to_string_u64(&self, value: u64) -> String {
+        value.to_string()
+    }
+    fn to_string_float(&self, value: f32) -> String {
+        value.to_string()
+    }
+    fn to_string_double(&self, value: f64) -> String {
+        value.to_string()
+    }
+    fn to_string_boolean(&self, value: bool) -> String {
+        value.to_string()
+    }
+    fn well_known_string(&self, value: String) -> String {
+        format!("uniffi 💚 {}!", value)
+    }
+}
+
+#[derive(Debug, Clone)]
+struct Optionneur;
+impl Optionneur {
+    fn new() -> Self {
+        Optionneur
+    }
+    fn sinon_string(&self, value: String) -> String {
+        value
+    }
+    fn sinon_null(&self, value: Option<String>) -> Option<String> {
+        value
+    }
+    fn sinon_boolean(&self, value: bool) -> bool {
+        value
+    }
+    fn sinon_sequence(&self, value: Vec<String>) -> Vec<String> {
+        value
+    }
+
+    fn sinon_zero(&self, value: Option<i32>) -> Option<i32> {
+        value
+    }
+
+    fn sinon_u8_dec(&self, value: u8) -> u8 {
+        value
+    }
+    fn sinon_i8_dec(&self, value: i8) -> i8 {
+        value
+    }
+    fn sinon_u16_dec(&self, value: u16) -> u16 {
+        value
+    }
+    fn sinon_i16_dec(&self, value: i16) -> i16 {
+        value
+    }
+    fn sinon_u32_dec(&self, value: u32) -> u32 {
+        value
+    }
+    fn sinon_i32_dec(&self, value: i32) -> i32 {
+        value
+    }
+    fn sinon_u64_dec(&self, value: u64) -> u64 {
+        value
+    }
+    fn sinon_i64_dec(&self, value: i64) -> i64 {
+        value
+    }
+
+    fn sinon_u8_hex(&self, value: u8) -> u8 {
+        value
+    }
+    fn sinon_i8_hex(&self, value: i8) -> i8 {
+        value
+    }
+    fn sinon_u16_hex(&self, value: u16) -> u16 {
+        value
+    }
+    fn sinon_i16_hex(&self, value: i16) -> i16 {
+        value
+    }
+    fn sinon_u32_hex(&self, value: u32) -> u32 {
+        value
+    }
+    fn sinon_i32_hex(&self, value: i32) -> i32 {
+        value
+    }
+    fn sinon_u64_hex(&self, value: u64) -> u64 {
+        value
+    }
+    fn sinon_i64_hex(&self, value: i64) -> i64 {
+        value
+    }
+
+    fn sinon_u32_oct(&self, value: u32) -> u32 {
+        value
+    }
+
+    fn sinon_f32(&self, value: f32) -> f32 {
+        value
+    }
+    fn sinon_f64(&self, value: f64) -> f64 {
+        value
+    }
+
+    fn sinon_enum(&self, value: Enumeration) -> Enumeration {
+        value
+    }
+}
+
+pub struct OptionneurDictionnaire {
+    i8_var: i8,
+    u8_var: u8,
+    i16_var: i16,
+    u16_var: u16,
+    i32_var: i32,
+    u32_var: u32,
+    i64_var: i64,
+    u64_var: u64,
+    float_var: f32,
+    double_var: f64,
+    boolean_var: bool,
+    string_var: String,
+    list_var: Vec<String>,
+    enumeration_var: Enumeration,
+    dictionnaire_var: Option<minusculeMAJUSCULEEnum>,
+}
+
+include!(concat!(env!("OUT_DIR"), "/rondpoint.uniffi.rs"));
--- a/third_party/rust/uniffi-example-rondpoint/src/rondpoint.udl
+++ b/third_party/rust/uniffi-example-rondpoint/src/rondpoint.udl
@ -0,0 +1,146 @@
+namespace rondpoint {
+  Dictionnaire copie_dictionnaire(Dictionnaire d);
+  Enumeration copie_enumeration(Enumeration e);
+  sequence<Enumeration> copie_enumerations(sequence<Enumeration> e);
+  record<DOMString, EnumerationAvecDonnees> copie_carte(record<DOMString, EnumerationAvecDonnees> c);
+  boolean switcheroo(boolean b);
+};
+
+dictionary minusculeMAJUSCULEDict {
+  boolean minusculeMAJUSCULEField;
+};
+
+enum minusculeMAJUSCULEEnum {
+  "minusculeMAJUSCULEVariant",
+};
+
+enum Enumeration {
+    "Un",
+    "Deux",
+    "Trois",
+};
+
+[Enum]
+interface EnumerationAvecDonnees {
+  Zero();
+  Un(u32 premier);
+  Deux(u32 premier, string second);
+};
+
+dictionary Dictionnaire {
+    Enumeration un;
+    boolean deux;
+    u8 petit_nombre;
+    u64 gros_nombre;
+};
+
+dictionary DictionnaireNombres {
+    u8 petit_nombre;
+    u16 court_nombre;
+    u32 nombre_simple;
+    u64 gros_nombre;
+};
+
+dictionary DictionnaireNombresSignes {
+    i8 petit_nombre;
+    i16 court_nombre;
+    i32 nombre_simple;
+    i64 gros_nombre;
+};
+
+interface Retourneur {
+  constructor();
+  i8 identique_i8(i8 value);
+  u8 identique_u8(u8 value);
+  i16 identique_i16(i16 value);
+  u16 identique_u16(u16 value);
+  i32 identique_i32(i32 value);
+  u32 identique_u32(u32 value);
+  i64 identique_i64(i64 value);
+  u64 identique_u64(u64 value);
+  float identique_float(float value);
+  double identique_double(double value);
+  boolean identique_boolean(boolean value);
+  string identique_string(string value);
+
+  DictionnaireNombresSignes identique_nombres_signes(DictionnaireNombresSignes value);
+  DictionnaireNombres       identique_nombres(DictionnaireNombres value);
+  OptionneurDictionnaire    identique_optionneur_dictionnaire(OptionneurDictionnaire value);
+};
+
+interface Stringifier {
+  constructor();
+  string well_known_string(string value);
+
+  string to_string_i8(i8 value);
+  string to_string_u8(u8 value);
+  string to_string_i16(i16 value);
+  string to_string_u16(u16 value);
+  string to_string_i32(i32 value);
+  string to_string_u32(u32 value);
+  string to_string_i64(i64 value);
+  string to_string_u64(u64 value);
+  string to_string_float(float value);
+  string to_string_double(double value);
+  string to_string_boolean(boolean value);
+};
+
+interface Optionneur {
+  constructor();
+  boolean sinon_boolean(optional boolean value = false);
+  string sinon_string(optional string value = "default");
+
+  sequence<string> sinon_sequence(optional sequence<string> value = []);
+
+  // Either sides of nullable.
+  string? sinon_null(optional string? value = null);
+  i32? sinon_zero(optional i32? value = 0);
+
+  // Decimal integers, all 42.
+  u8 sinon_u8_dec(optional u8 value = 42);
+  i8 sinon_i8_dec(optional i8 value = -42);
+  u16 sinon_u16_dec(optional u16 value = 42);
+  i16 sinon_i16_dec(optional i16 value = 42);
+  u32 sinon_u32_dec(optional u32 value = 42);
+  i32 sinon_i32_dec(optional i32 value = 42);
+  u64 sinon_u64_dec(optional u64 value = 42);
+  i64 sinon_i64_dec(optional i64 value = 42);
+
+  // Hexadecimal, including negatgives.
+  u8 sinon_u8_hex(optional u8 value = 0xff);
+  i8 sinon_i8_hex(optional i8 value = -0x7f);
+  u16 sinon_u16_hex(optional u16 value = 0xffff);
+  i16 sinon_i16_hex(optional i16 value = 0x7f);
+  u32 sinon_u32_hex(optional u32 value = 0xffffffff);
+  i32 sinon_i32_hex(optional i32 value = 0x7fffffff);
+  u64 sinon_u64_hex(optional u64 value = 0xffffffffffffffff);
+  i64 sinon_i64_hex(optional i64 value = 0x7fffffffffffffff);
+
+  // Octal, FWIW.
+  u32 sinon_u32_oct(optional u32 value = 0755);
+
+  // Floats
+  f32 sinon_f32(optional f32 value = 42.0);
+  f64 sinon_f64(optional f64 value = 42.1);
+
+  // Enums, which we have to treat as strings in the UDL frontend.
+  Enumeration sinon_enum(optional Enumeration value = "Trois");
+};
+
+dictionary OptionneurDictionnaire {
+  i8 i8_var = -8;
+  u8 u8_var = 8;
+  i16 i16_var = -0x10;
+  u16 u16_var = 0x10;
+  i32 i32_var = -32;
+  u32 u32_var = 32;
+  i64 i64_var = -64;
+  u64 u64_var = 64;
+  float float_var = 4.0;
+  double double_var = 8.0;
+  boolean boolean_var = true;
+  string string_var = "default";
+  sequence<string> list_var = [];
+  Enumeration enumeration_var = "DEUX";
+  minusculeMAJUSCULEEnum? dictionnaire_var = null;
+};
--- a/third_party/rust/uniffi-example-rondpoint/tests/bindings/test_rondpoint.kts
+++ b/third_party/rust/uniffi-example-rondpoint/tests/bindings/test_rondpoint.kts
@ -0,0 +1,250 @@
+import uniffi.rondpoint.*
+
+val dico = Dictionnaire(Enumeration.DEUX, true, 0u, 123456789u)
+val copyDico = copieDictionnaire(dico)
+assert(dico == copyDico)
+
+assert(copieEnumeration(Enumeration.DEUX) == Enumeration.DEUX)
+assert(copieEnumerations(listOf(Enumeration.UN, Enumeration.DEUX)) == listOf(Enumeration.UN, Enumeration.DEUX))
+assert(copieCarte(mapOf(
+    "0" to EnumerationAvecDonnees.Zero,
+    "1" to EnumerationAvecDonnees.Un(1u),
+    "2" to EnumerationAvecDonnees.Deux(2u, "deux")
+)) == mapOf(
+    "0" to EnumerationAvecDonnees.Zero,
+    "1" to EnumerationAvecDonnees.Un(1u),
+    "2" to EnumerationAvecDonnees.Deux(2u, "deux")
+))
+
+val var1: EnumerationAvecDonnees = EnumerationAvecDonnees.Zero
+val var2: EnumerationAvecDonnees = EnumerationAvecDonnees.Un(1u)
+val var3: EnumerationAvecDonnees = EnumerationAvecDonnees.Un(2u)
+assert(var1 != var2)
+assert(var2 != var3)
+assert(var1 == EnumerationAvecDonnees.Zero)
+assert(var1 != EnumerationAvecDonnees.Un(1u))
+assert(var2 == EnumerationAvecDonnees.Un(1u))
+
+assert(switcheroo(false))
+
+// Test the roundtrip across the FFI.
+// This shows that the values we send come back in exactly the same state as we sent them.
+// i.e. it shows that lowering from kotlin and lifting into rust is symmetrical with 
+//      lowering from rust and lifting into kotlin.
+val rt = Retourneur()
+
+fun <T> List<T>.affirmAllerRetour(fn: (T) -> T) {
+    this.forEach { v ->
+        assert(fn.invoke(v) == v) { "$fn($v)" }
+    }
+}
+
+// Booleans
+listOf(true, false).affirmAllerRetour(rt::identiqueBoolean)
+
+// Bytes.
+listOf(Byte.MIN_VALUE, Byte.MAX_VALUE).affirmAllerRetour(rt::identiqueI8)
+listOf(0x00, 0xFF).map { it.toUByte() }.affirmAllerRetour(rt::identiqueU8)
+
+// Shorts
+listOf(Short.MIN_VALUE, Short.MAX_VALUE).affirmAllerRetour(rt::identiqueI16)
+listOf(0x0000, 0xFFFF).map { it.toUShort() }.affirmAllerRetour(rt::identiqueU16)
+
+// Ints
+listOf(0, 1, -1, Int.MIN_VALUE, Int.MAX_VALUE).affirmAllerRetour(rt::identiqueI32)
+listOf(0x00000000, 0xFFFFFFFF).map { it.toUInt() }.affirmAllerRetour(rt::identiqueU32)
+
+// Longs
+listOf(0L, 1L, -1L, Long.MIN_VALUE, Long.MAX_VALUE).affirmAllerRetour(rt::identiqueI64)
+listOf(0u, 1u, ULong.MIN_VALUE, ULong.MAX_VALUE).affirmAllerRetour(rt::identiqueU64)
+
+// Floats
+listOf(0.0F, 0.5F, 0.25F, Float.MIN_VALUE, Float.MAX_VALUE).affirmAllerRetour(rt::identiqueFloat)
+
+// Doubles
+listOf(0.0, 1.0, Double.MIN_VALUE, Double.MAX_VALUE).affirmAllerRetour(rt::identiqueDouble)
+
+// Strings
+listOf("", "abc", "null\u0000byte", "été", "ښي لاس ته لوستلو لوستل", "😻emoji 👨‍👧‍👦multi-emoji, 🇨🇭a flag, a canal, panama")
+    .affirmAllerRetour(rt::identiqueString)
+
+listOf(-1, 0, 1).map { DictionnaireNombresSignes(it.toByte(), it.toShort(), it.toInt(), it.toLong()) }
+    .affirmAllerRetour(rt::identiqueNombresSignes)
+
+listOf(0, 1).map { DictionnaireNombres(it.toUByte(), it.toUShort(), it.toUInt(), it.toULong()) }
+    .affirmAllerRetour(rt::identiqueNombres)
+
+
+rt.destroy()
+
+// Test one way across the FFI.
+//
+// We send one representation of a value to lib.rs, and it transforms it into another, a string.
+// lib.rs sends the string back, and then we compare here in kotlin.
+//
+// This shows that the values are transformed into strings the same way in both kotlin and rust.
+// i.e. if we assume that the string return works (we test this assumption elsewhere)
+//      we show that lowering from kotlin and lifting into rust has values that both kotlin and rust
+//      both stringify in the same way. i.e. the same values.
+//
+// If we roundtripping proves the symmetry of our lowering/lifting from here to rust, and lowering/lifting from rust t here,
+// and this convinces us that lowering/lifting from here to rust is correct, then 
+// together, we've shown the correctness of the return leg.
+val st = Stringifier()
+
+typealias StringyEquals<T> = (observed: String, expected: T) -> Boolean
+fun <T> List<T>.affirmEnchaine(
+    fn: (T) -> String,
+    equals: StringyEquals<T> = { obs, exp -> obs == exp.toString() }
+) {
+    this.forEach { exp ->
+        val obs = fn.invoke(exp)
+        assert(equals(obs, exp)) { "$fn($exp): observed=$obs, expected=$exp" }
+    }
+}
+
+// Test the efficacy of the string transport from rust. If this fails, but everything else 
+// works, then things are very weird.
+val wellKnown = st.wellKnownString("kotlin")
+assert("uniffi 💚 kotlin!" == wellKnown) { "wellKnownString 'uniffi 💚 kotlin!' == '$wellKnown'" }
+
+// Booleans
+listOf(true, false).affirmEnchaine(st::toStringBoolean)
+
+// Bytes.
+listOf(Byte.MIN_VALUE, Byte.MAX_VALUE).affirmEnchaine(st::toStringI8)
+listOf(UByte.MIN_VALUE, UByte.MAX_VALUE).affirmEnchaine(st::toStringU8)
+
+// Shorts
+listOf(Short.MIN_VALUE, Short.MAX_VALUE).affirmEnchaine(st::toStringI16)
+listOf(UShort.MIN_VALUE, UShort.MAX_VALUE).affirmEnchaine(st::toStringU16)
+
+// Ints
+listOf(0, 1, -1, Int.MIN_VALUE, Int.MAX_VALUE).affirmEnchaine(st::toStringI32)
+listOf(0u, 1u, UInt.MIN_VALUE, UInt.MAX_VALUE).affirmEnchaine(st::toStringU32)
+
+// Longs
+listOf(0L, 1L, -1L, Long.MIN_VALUE, Long.MAX_VALUE).affirmEnchaine(st::toStringI64)
+listOf(0u, 1u, ULong.MIN_VALUE, ULong.MAX_VALUE).affirmEnchaine(st::toStringU64)
+
+// Floats
+// MIN_VAUE is 1.4E-45. Accuracy and formatting get weird at small sizes.
+listOf(0.0F, 1.0F, -1.0F, Float.MIN_VALUE, Float.MAX_VALUE).affirmEnchaine(st::toStringFloat) { s, n -> s.toFloat() == n }
+
+// Doubles
+// MIN_VALUE is 4.9E-324. Accuracy and formatting get weird at small sizes.
+listOf(0.0, 1.0, -1.0, Double.MIN_VALUE, Double.MAX_VALUE).affirmEnchaine(st::toStringDouble)  { s, n -> s.toDouble() == n }
+
+st.destroy()
+
+// Prove to ourselves that default arguments are being used.
+// Step 1: call the methods without arguments, and check against the UDL.
+val op = Optionneur()
+
+assert(op.sinonString() == "default")
+
+assert(op.sinonBoolean() == false)
+
+assert(op.sinonSequence() == listOf<String>())
+
+// optionals
+assert(op.sinonNull() == null)
+assert(op.sinonZero() == 0)
+
+// decimal integers
+assert(op.sinonI8Dec() == (-42).toByte())
+assert(op.sinonU8Dec() == 42.toUByte())
+assert(op.sinonI16Dec() == 42.toShort())
+assert(op.sinonU16Dec() == 42.toUShort())
+assert(op.sinonI32Dec() == 42)
+assert(op.sinonU32Dec() == 42.toUInt())
+assert(op.sinonI64Dec() == 42L)
+assert(op.sinonU64Dec() == 42uL)
+
+// hexadecimal integers
+assert(op.sinonI8Hex() == (-0x7f).toByte())
+assert(op.sinonU8Hex() == 0xff.toUByte())
+assert(op.sinonI16Hex() == 0x7f.toShort())
+assert(op.sinonU16Hex() == 0xffff.toUShort())
+assert(op.sinonI32Hex() == 0x7fffffff)
+assert(op.sinonU32Hex() == 0xffffffff.toUInt())
+assert(op.sinonI64Hex() == 0x7fffffffffffffffL)
+assert(op.sinonU64Hex() == 0xffffffffffffffffuL)
+
+// octal integers
+assert(op.sinonU32Oct() == 493u) // 0o755
+
+// floats
+assert(op.sinonF32() == 42.0f)
+assert(op.sinonF64() == 42.1)
+
+// enums
+assert(op.sinonEnum() == Enumeration.TROIS)
+
+// Step 2. Convince ourselves that if we pass something else, then that changes the output.
+//         We have shown something coming out of the sinon methods, but without eyeballing the Rust
+//         we can't be sure that the arguments will change the return value.
+listOf("foo", "bar").affirmAllerRetour(op::sinonString)
+listOf(true, false).affirmAllerRetour(op::sinonBoolean)
+listOf(listOf("a", "b"), listOf()).affirmAllerRetour(op::sinonSequence)
+
+// optionals
+listOf("0", "1").affirmAllerRetour(op::sinonNull)
+listOf(0, 1).affirmAllerRetour(op::sinonZero)
+
+// integers
+listOf(0, 1).map { it.toUByte() }.affirmAllerRetour(op::sinonU8Dec)
+listOf(0, 1).map { it.toByte() }.affirmAllerRetour(op::sinonI8Dec)
+listOf(0, 1).map { it.toUShort() }.affirmAllerRetour(op::sinonU16Dec)
+listOf(0, 1).map { it.toShort() }.affirmAllerRetour(op::sinonI16Dec)
+listOf(0, 1).map { it.toUInt() }.affirmAllerRetour(op::sinonU32Dec)
+listOf(0, 1).map { it.toInt() }.affirmAllerRetour(op::sinonI32Dec)
+listOf(0, 1).map { it.toULong() }.affirmAllerRetour(op::sinonU64Dec)
+listOf(0, 1).map { it.toLong() }.affirmAllerRetour(op::sinonI64Dec)
+
+listOf(0, 1).map { it.toUByte() }.affirmAllerRetour(op::sinonU8Hex)
+listOf(0, 1).map { it.toByte() }.affirmAllerRetour(op::sinonI8Hex)
+listOf(0, 1).map { it.toUShort() }.affirmAllerRetour(op::sinonU16Hex)
+listOf(0, 1).map { it.toShort() }.affirmAllerRetour(op::sinonI16Hex)
+listOf(0, 1).map { it.toUInt() }.affirmAllerRetour(op::sinonU32Hex)
+listOf(0, 1).map { it.toInt() }.affirmAllerRetour(op::sinonI32Hex)
+listOf(0, 1).map { it.toULong() }.affirmAllerRetour(op::sinonU64Hex)
+listOf(0, 1).map { it.toLong() }.affirmAllerRetour(op::sinonI64Hex)
+
+listOf(0, 1).map { it.toUInt() }.affirmAllerRetour(op::sinonU32Oct)
+
+// floats
+listOf(0.0f, 1.0f).affirmAllerRetour(op::sinonF32)
+listOf(0.0, 1.0).affirmAllerRetour(op::sinonF64)
+
+// enums
+Enumeration.values().toList().affirmAllerRetour(op::sinonEnum)
+
+op.destroy()
+
+// Testing defaulting properties in record types.
+val defaultes = OptionneurDictionnaire()
+val explicite = OptionneurDictionnaire(
+    i8Var = -8,
+    u8Var = 8u,
+    i16Var = -16,
+    u16Var = 0x10u,
+    i32Var = -32,
+    u32Var = 32u,
+    i64Var = -64L,
+    u64Var = 64uL,
+    floatVar = 4.0f,
+    doubleVar = 8.0,
+    booleanVar = true,
+    stringVar = "default",
+    listVar = listOf(),
+    enumerationVar = Enumeration.DEUX,
+    dictionnaireVar = null
+)
+assert(defaultes == explicite)
+
+// …and makes sure they travel across and back the FFI.
+val rt2 = Retourneur()
+listOf(defaultes).affirmAllerRetour(rt2::identiqueOptionneurDictionnaire)
+
+rt2.destroy()
--- a/third_party/rust/uniffi-example-rondpoint/tests/bindings/test_rondpoint.py
+++ b/third_party/rust/uniffi-example-rondpoint/tests/bindings/test_rondpoint.py
@ -0,0 +1,146 @@
+import sys
+import ctypes
+from rondpoint import *
+
+dico = Dictionnaire(Enumeration.DEUX, True, 0, 123456789)
+copyDico = copie_dictionnaire(dico)
+assert dico == copyDico
+
+assert copie_enumeration(Enumeration.DEUX) == Enumeration.DEUX
+assert copie_enumerations([Enumeration.UN, Enumeration.DEUX]) == [Enumeration.UN, Enumeration.DEUX]
+assert copie_carte({
+    "0": EnumerationAvecDonnees.ZERO(),
+    "1": EnumerationAvecDonnees.UN(1),
+    "2": EnumerationAvecDonnees.DEUX(2, "deux"),
+}) == {
+    "0": EnumerationAvecDonnees.ZERO(),
+    "1": EnumerationAvecDonnees.UN(1),
+    "2": EnumerationAvecDonnees.DEUX(2, "deux"),
+}
+
+assert switcheroo(False) is True
+
+assert EnumerationAvecDonnees.ZERO() != EnumerationAvecDonnees.UN(1)
+assert EnumerationAvecDonnees.UN(1) == EnumerationAvecDonnees.UN(1)
+assert EnumerationAvecDonnees.UN(1) != EnumerationAvecDonnees.UN(2)
+
+# Test the roundtrip across the FFI.
+# This shows that the values we send come back in exactly the same state as we sent them.
+# i.e. it shows that lowering from python and lifting into rust is symmetrical with
+#      lowering from rust and lifting into python.
+rt = Retourneur()
+
+def affirmAllerRetour(vals, identique):
+    for v in vals:
+        id_v = identique(v)
+        assert id_v == v, f"Round-trip failure: {v} => {id_v}"
+
+MIN_I8 = -1 * 2**7
+MAX_I8 = 2**7 - 1
+MIN_I16 = -1 * 2**15
+MAX_I16 = 2**15 - 1
+MIN_I32 = -1 * 2**31
+MAX_I32 = 2**31 - 1
+MIN_I64 = -1 * 2**31
+MAX_I64 = 2**31 - 1
+
+# Python floats are always doubles, so won't round-trip through f32 correctly.
+# This truncates them appropriately.
+F32_ONE_THIRD = ctypes.c_float(1.0 / 3).value
+
+# Booleans
+affirmAllerRetour([True, False], rt.identique_boolean)
+
+# Bytes.
+affirmAllerRetour([MIN_I8, -1, 0, 1, MAX_I8], rt.identique_i8)
+affirmAllerRetour([0x00, 0x12, 0xFF], rt.identique_u8)
+
+# Shorts
+affirmAllerRetour([MIN_I16, -1, 0, 1, MAX_I16], rt.identique_i16)
+affirmAllerRetour([0x0000, 0x1234, 0xFFFF], rt.identique_u16)
+
+# Ints
+affirmAllerRetour([MIN_I32, -1, 0, 1, MAX_I32], rt.identique_i32)
+affirmAllerRetour([0x00000000, 0x12345678, 0xFFFFFFFF], rt.identique_u32)
+
+# Longs
+affirmAllerRetour([MIN_I64, -1, 0, 1, MAX_I64], rt.identique_i64)
+affirmAllerRetour([0x0000000000000000, 0x1234567890ABCDEF, 0xFFFFFFFFFFFFFFFF], rt.identique_u64)
+
+# Floats
+affirmAllerRetour([0.0, 0.5, 0.25, 1.0, F32_ONE_THIRD], rt.identique_float)
+
+# Doubles
+affirmAllerRetour(
+  [0.0, 0.5, 0.25, 1.0, 1.0 / 3, sys.float_info.max, sys.float_info.min],
+  rt.identique_double
+)
+
+# Strings
+affirmAllerRetour(
+  ["", "abc", "été", "ښي لاس ته لوستلو لوستل", "😻emoji 👨‍👧‍👦multi-emoji, 🇨🇭a flag, a canal, panama"],
+  rt.identique_string
+)
+
+# Test one way across the FFI.
+#
+# We send one representation of a value to lib.rs, and it transforms it into another, a string.
+# lib.rs sends the string back, and then we compare here in python.
+#
+# This shows that the values are transformed into strings the same way in both python and rust.
+# i.e. if we assume that the string return works (we test this assumption elsewhere)
+#      we show that lowering from python and lifting into rust has values that both python and rust
+#      both stringify in the same way. i.e. the same values.
+#
+# If we roundtripping proves the symmetry of our lowering/lifting from here to rust, and lowering/lifting from rust to here,
+# and this convinces us that lowering/lifting from here to rust is correct, then
+# together, we've shown the correctness of the return leg.
+st = Stringifier()
+
+def affirmEnchaine(vals, toString, rustyStringify=lambda v: str(v).lower()):
+    for v in vals:
+        str_v = toString(v)
+        assert rustyStringify(v) == str_v, f"String compare error {v} => {str_v}"
+
+# Test the efficacy of the string transport from rust. If this fails, but everything else
+# works, then things are very weird.
+wellKnown = st.well_known_string("python")
+assert "uniffi 💚 python!" == wellKnown
+
+# Booleans
+affirmEnchaine([True, False], st.to_string_boolean)
+
+# Bytes.
+affirmEnchaine([MIN_I8, -1, 0, 1, MAX_I8], st.to_string_i8)
+affirmEnchaine([0x00, 0x12, 0xFF], st.to_string_u8)
+
+# Shorts
+affirmEnchaine([MIN_I16, -1, 0, 1, MAX_I16], st.to_string_i16)
+affirmEnchaine([0x0000, 0x1234, 0xFFFF], st.to_string_u16)
+
+# Ints
+affirmEnchaine([MIN_I32, -1, 0, 1, MAX_I32], st.to_string_i32)
+affirmEnchaine([0x00000000, 0x12345678, 0xFFFFFFFF], st.to_string_u32)
+
+# Longs
+affirmEnchaine([MIN_I64, -1, 0, 1, MAX_I64], st.to_string_i64)
+affirmEnchaine([0x0000000000000000, 0x1234567890ABCDEF, 0xFFFFFFFFFFFFFFFF], st.to_string_u64)
+
+# Floats
+def rustyFloatToStr(v):
+    """Stringify a float in the same way that rust seems to."""
+    # Rust doesn't include the decimal part of whole enumber floats when stringifying.
+    if int(v) == v:
+        return str(int(v))
+    return str(v)
+
+affirmEnchaine([0.0, 0.5, 0.25, 1.0], st.to_string_float, rustyFloatToStr)
+assert st.to_string_float(F32_ONE_THIRD) == "0.33333334" # annoyingly different string repr
+
+# Doubles
+# TODO: float_info.max/float_info.min don't stringify-roundtrip properly yet, TBD.
+affirmEnchaine(
+  [0.0, 0.5, 0.25, 1.0, 1.0 / 3],
+  st.to_string_double,
+  rustyFloatToStr,
+)
--- a/third_party/rust/uniffi-example-rondpoint/tests/bindings/test_rondpoint.rb
+++ b/third_party/rust/uniffi-example-rondpoint/tests/bindings/test_rondpoint.rb
@ -0,0 +1,142 @@
+# frozen_string_literal: true
+
+require 'test/unit'
+require 'rondpoint'
+
+include Test::Unit::Assertions
+include Rondpoint
+
+dico = Dictionnaire.new Enumeration::DEUX, true, 0, 123_456_789
+
+assert_equal dico, Rondpoint.copie_dictionnaire(dico)
+
+assert_equal Rondpoint.copie_enumeration(Enumeration::DEUX), Enumeration::DEUX
+
+assert_equal Rondpoint.copie_enumerations([
+                                            Enumeration::UN,
+                                            Enumeration::DEUX
+                                          ]), [Enumeration::UN, Enumeration::DEUX]
+
+assert_equal Rondpoint.copie_carte({
+                                     '0' => EnumerationAvecDonnees::ZERO.new,
+                                     '1' => EnumerationAvecDonnees::UN.new(1),
+                                     '2' => EnumerationAvecDonnees::DEUX.new(2, 'deux')
+                                   }), {
+                                     '0' => EnumerationAvecDonnees::ZERO.new,
+                                     '1' => EnumerationAvecDonnees::UN.new(1),
+                                     '2' => EnumerationAvecDonnees::DEUX.new(2, 'deux')
+                                   }
+
+assert Rondpoint.switcheroo(false)
+
+assert_not_equal EnumerationAvecDonnees::ZERO.new, EnumerationAvecDonnees::UN.new(1)
+assert_equal EnumerationAvecDonnees::UN.new(1), EnumerationAvecDonnees::UN.new(1)
+assert_not_equal EnumerationAvecDonnees::UN.new(1), EnumerationAvecDonnees::UN.new(2)
+
+# Test the roundtrip across the FFI.
+# This shows that the values we send come back in exactly the same state as we sent them.
+# i.e. it shows that lowering from ruby and lifting into rust is symmetrical with
+#      lowering from rust and lifting into ruby.
+RT = Retourneur.new
+
+def affirm_aller_retour(vals, fn_name)
+  vals.each do |v|
+    id_v = RT.public_send fn_name, v
+
+    assert_equal id_v, v, "Round-trip failure: #{v} => #{id_v}"
+  end
+end
+
+MIN_I8 = -1 * 2**7
+MAX_I8 = 2**7 - 1
+MIN_I16 = -1 * 2**15
+MAX_I16 = 2**15 - 1
+MIN_I32 = -1 * 2**31
+MAX_I32 = 2**31 - 1
+MIN_I64 = -1 * 2**31
+MAX_I64 = 2**31 - 1
+
+# Ruby floats are always doubles, so won't round-trip through f32 correctly.
+# This truncates them appropriately.
+F32_ONE_THIRD = [1.0 / 3].pack('f').unpack('f')[0]
+
+# Booleans
+affirm_aller_retour([true, false], :identique_boolean)
+
+# Bytes.
+affirm_aller_retour([MIN_I8, -1, 0, 1, MAX_I8], :identique_i8)
+affirm_aller_retour([0x00, 0x12, 0xFF], :identique_u8)
+
+# Shorts
+affirm_aller_retour([MIN_I16, -1, 0, 1, MAX_I16], :identique_i16)
+affirm_aller_retour([0x0000, 0x1234, 0xFFFF], :identique_u16)
+
+# Ints
+affirm_aller_retour([MIN_I32, -1, 0, 1, MAX_I32], :identique_i32)
+affirm_aller_retour([0x00000000, 0x12345678, 0xFFFFFFFF], :identique_u32)
+
+# Longs
+affirm_aller_retour([MIN_I64, -1, 0, 1, MAX_I64], :identique_i64)
+affirm_aller_retour([0x0000000000000000, 0x1234567890ABCDEF, 0xFFFFFFFFFFFFFFFF], :identique_u64)
+
+# Floats
+affirm_aller_retour([0.0, 0.5, 0.25, 1.0, F32_ONE_THIRD], :identique_float)
+
+# Doubles
+affirm_aller_retour(
+  [0.0, 0.5, 0.25, 1.0, 1.0 / 3, Float::MAX, Float::MIN],
+  :identique_double
+)
+
+# Strings
+affirm_aller_retour(
+  ['', 'abc', 'été', 'ښي لاس ته لوستلو لوستل',
+   '😻emoji 👨‍👧‍👦multi-emoji, 🇨🇭a flag, a canal, panama'],
+  :identique_string
+)
+
+# Test one way across the FFI.
+#
+# We send one representation of a value to lib.rs, and it transforms it into another, a string.
+# lib.rs sends the string back, and then we compare here in ruby.
+#
+# This shows that the values are transformed into strings the same way in both ruby and rust.
+# i.e. if we assume that the string return works (we test this assumption elsewhere)
+#      we show that lowering from ruby and lifting into rust has values that both ruby and rust
+#      both stringify in the same way. i.e. the same values.
+#
+# If we roundtripping proves the symmetry of our lowering/lifting from here to rust, and lowering/lifting from rust to here,
+# and this convinces us that lowering/lifting from here to rust is correct, then
+# together, we've shown the correctness of the return leg.
+ST = Stringifier.new
+
+def affirm_enchaine(vals, fn_name)
+  vals.each do |v|
+    str_v = ST.public_send fn_name, v
+
+    assert_equal v.to_s, str_v, "String compare error #{v} => #{str_v}"
+  end
+end
+
+# Test the efficacy of the string transport from rust. If this fails, but everything else
+# works, then things are very weird.
+assert_equal ST.well_known_string('ruby'), 'uniffi 💚 ruby!'
+
+# Booleans
+affirm_enchaine([true, false], :to_string_boolean)
+
+# Bytes.
+affirm_enchaine([MIN_I8, -1, 0, 1, MAX_I8], :to_string_i8)
+affirm_enchaine([0x00, 0x12, 0xFF], :to_string_u8)
+
+# Shorts
+affirm_enchaine([MIN_I16, -1, 0, 1, MAX_I16], :to_string_i16)
+affirm_enchaine([0x0000, 0x1234, 0xFFFF], :to_string_u16)
+
+# Ints
+affirm_enchaine([MIN_I32, -1, 0, 1, MAX_I32], :to_string_i32)
+affirm_enchaine([0x00000000, 0x12345678, 0xFFFFFFFF], :to_string_u32)
+
+# Longs
+affirm_enchaine([MIN_I64, -1, 0, 1, MAX_I64], :to_string_i64)
+affirm_enchaine([0x0000000000000000, 0x1234567890ABCDEF, 0xFFFFFFFFFFFFFFFF], :to_string_u64)
--- a/third_party/rust/uniffi-example-rondpoint/tests/bindings/test_rondpoint.swift
+++ b/third_party/rust/uniffi-example-rondpoint/tests/bindings/test_rondpoint.swift
@ -0,0 +1,232 @@
+import rondpoint
+
+let dico = Dictionnaire(un: .deux, deux: false, petitNombre: 0, grosNombre: 123456789)
+let copyDico = copieDictionnaire(d: dico)
+assert(dico == copyDico)
+
+assert(copieEnumeration(e: .deux) == .deux)
+assert(copieEnumerations(e: [.un, .deux]) == [.un, .deux])
+assert(copieCarte(c:
+    ["0": .zero,
+    "1": .un(premier: 1),
+    "2": .deux(premier: 2, second: "deux")
+]) == [
+    "0": .zero,
+    "1": .un(premier: 1),
+    "2": .deux(premier: 2, second: "deux")
+])
+
+assert(EnumerationAvecDonnees.zero != EnumerationAvecDonnees.un(premier: 1))
+assert(EnumerationAvecDonnees.un(premier: 1) == EnumerationAvecDonnees.un(premier: 1))
+assert(EnumerationAvecDonnees.un(premier: 1) != EnumerationAvecDonnees.un(premier: 2))
+
+
+assert(switcheroo(b: false))
+
+// Test the roundtrip across the FFI.
+// This shows that the values we send come back in exactly the same state as we sent them.
+// i.e. it shows that lowering from swift and lifting into rust is symmetrical with 
+//      lowering from rust and lifting into swift.
+let rt = Retourneur()
+
+// Booleans
+[true, false].affirmAllerRetour(rt.identiqueBoolean)
+
+// Bytes.
+[.min, .max].affirmAllerRetour(rt.identiqueI8)
+[0x00, 0xFF].map { $0 as UInt8 }.affirmAllerRetour(rt.identiqueU8)
+
+// Shorts
+[.min, .max].affirmAllerRetour(rt.identiqueI16)
+[0x0000, 0xFFFF].map { $0 as UInt16 }.affirmAllerRetour(rt.identiqueU16)
+
+// Ints
+[0, 1, -1, .min, .max].affirmAllerRetour(rt.identiqueI32)
+[0x00000000, 0xFFFFFFFF].map { $0 as UInt32 }.affirmAllerRetour(rt.identiqueU32)
+
+// Longs
+[.zero, 1, -1, .min, .max].affirmAllerRetour(rt.identiqueI64)
+[.zero, 1, .min, .max].affirmAllerRetour(rt.identiqueU64)
+
+// Floats
+[.zero, 1, 0.25, .leastNonzeroMagnitude, .greatestFiniteMagnitude].affirmAllerRetour(rt.identiqueFloat)
+
+// Doubles
+[0.0, 1.0, .leastNonzeroMagnitude, .greatestFiniteMagnitude].affirmAllerRetour(rt.identiqueDouble)
+
+// Strings
+["", "abc", "null\0byte", "été", "ښي لاس ته لوستلو لوستل", "😻emoji 👨‍👧‍👦multi-emoji, 🇨🇭a flag, a canal, panama"]
+    .affirmAllerRetour(rt.identiqueString)
+
+// Test one way across the FFI.
+//
+// We send one representation of a value to lib.rs, and it transforms it into another, a string.
+// lib.rs sends the string back, and then we compare here in swift.
+//
+// This shows that the values are transformed into strings the same way in both swift and rust.
+// i.e. if we assume that the string return works (we test this assumption elsewhere)
+//      we show that lowering from swift and lifting into rust has values that both swift and rust
+//      both stringify in the same way. i.e. the same values.
+//
+// If we roundtripping proves the symmetry of our lowering/lifting from here to rust, and lowering/lifting from rust t here,
+// and this convinces us that lowering/lifting from here to rust is correct, then 
+// together, we've shown the correctness of the return leg.
+let st = Stringifier()
+
+// Test the effigacy of the string transport from rust. If this fails, but everything else 
+// works, then things are very weird.
+let wellKnown = st.wellKnownString(value: "swift")
+assert("uniffi 💚 swift!" == wellKnown, "wellKnownString 'uniffi 💚 swift!' == '\(wellKnown)'")
+
+// Booleans
+[true, false].affirmEnchaine(st.toStringBoolean)
+
+// Bytes.
+[.min, .max].affirmEnchaine(st.toStringI8)
+[.min, .max].affirmEnchaine(st.toStringU8)
+
+// Shorts
+[.min, .max].affirmEnchaine(st.toStringI16)
+[.min, .max].affirmEnchaine(st.toStringU16)
+
+// Ints
+[0, 1, -1, .min, .max].affirmEnchaine(st.toStringI32)
+[0, 1, .min, .max].affirmEnchaine(st.toStringU32)
+
+// Longs
+[.zero, 1, -1, .min, .max].affirmEnchaine(st.toStringI64)
+[.zero, 1, .min, .max].affirmEnchaine(st.toStringU64)
+
+// Floats
+[.zero, 1, -1, .leastNonzeroMagnitude, .greatestFiniteMagnitude].affirmEnchaine(st.toStringFloat) { Float.init($0) == $1 }
+
+// Doubles
+[.zero, 1, -1, .leastNonzeroMagnitude, .greatestFiniteMagnitude].affirmEnchaine(st.toStringDouble) { Double.init($0) == $1 }
+
+// Some extension functions for testing the results of roundtripping and stringifying
+extension Array where Element: Equatable {
+    static func defaultEquals(_ observed: String, expected: Element) -> Bool {
+        let exp = "\(expected)"
+        return observed == exp
+    }
+
+    func affirmEnchaine(_ fn: (Element) -> String, equals: (String, Element) -> Bool = defaultEquals) {
+        self.forEach { v in
+            let obs = fn(v)
+            assert(equals(obs, v), "toString_\(type(of:v))(\(v)): observed=\(obs), expected=\(v)")
+        }
+    }
+
+    func affirmAllerRetour(_ fn: (Element) -> Element) {
+        self.forEach { v in
+            assert(fn(v) == v, "identique_\(type(of:v))(\(v))")
+        }
+    }
+}
+
+// Prove to ourselves that default arguments are being used.
+// Step 1: call the methods without arguments, and check against the UDL.
+let op = Optionneur()
+
+assert(op.sinonString() == "default")
+
+assert(op.sinonBoolean() == false)
+
+assert(op.sinonSequence() == [])
+
+// optionals
+assert(op.sinonNull() == nil)
+assert(op.sinonZero() == 0)
+
+// decimal integers
+assert(op.sinonU8Dec() == UInt8(42))
+assert(op.sinonI8Dec() == Int8(-42))
+assert(op.sinonU16Dec() == UInt16(42))
+assert(op.sinonI16Dec() == Int16(42))
+assert(op.sinonU32Dec() == UInt32(42))
+assert(op.sinonI32Dec() == Int32(42))
+assert(op.sinonU64Dec() == UInt64(42))
+assert(op.sinonI64Dec() == Int64(42))
+
+// hexadecimal integers
+assert(op.sinonU8Hex() == UInt8(0xff))
+assert(op.sinonI8Hex() == Int8(-0x7f))
+assert(op.sinonU16Hex() == UInt16(0xffff))
+assert(op.sinonI16Hex() == Int16(0x7f))
+assert(op.sinonU32Hex() == UInt32(0xffffffff))
+assert(op.sinonI32Hex() == Int32(0x7fffffff))
+assert(op.sinonU64Hex() == UInt64(0xffffffffffffffff))
+assert(op.sinonI64Hex() == Int64(0x7fffffffffffffff))
+
+// octal integers
+assert(op.sinonU32Oct() == UInt32(0o755))
+
+// floats
+assert(op.sinonF32() == 42.0)
+assert(op.sinonF64() == Double(42.1))
+
+// enums
+assert(op.sinonEnum() == .trois)
+
+// Step 2. Convince ourselves that if we pass something else, then that changes the output.
+//         We have shown something coming out of the sinon methods, but without eyeballing the Rust
+//         we can't be sure that the arguments will change the return value.
+["foo", "bar"].affirmAllerRetour(op.sinonString)
+[true, false].affirmAllerRetour(op.sinonBoolean)
+[["a", "b"], []].affirmAllerRetour(op.sinonSequence)
+
+// optionals
+["0", "1"].affirmAllerRetour(op.sinonNull)
+[0, 1].affirmAllerRetour(op.sinonZero)
+
+// integers
+[0, 1].affirmAllerRetour(op.sinonU8Dec)
+[0, 1].affirmAllerRetour(op.sinonI8Dec)
+[0, 1].affirmAllerRetour(op.sinonU16Dec)
+[0, 1].affirmAllerRetour(op.sinonI16Dec)
+[0, 1].affirmAllerRetour(op.sinonU32Dec)
+[0, 1].affirmAllerRetour(op.sinonI32Dec)
+[0, 1].affirmAllerRetour(op.sinonU64Dec)
+[0, 1].affirmAllerRetour(op.sinonI64Dec)
+
+[0, 1].affirmAllerRetour(op.sinonU8Hex)
+[0, 1].affirmAllerRetour(op.sinonI8Hex)
+[0, 1].affirmAllerRetour(op.sinonU16Hex)
+[0, 1].affirmAllerRetour(op.sinonI16Hex)
+[0, 1].affirmAllerRetour(op.sinonU32Hex)
+[0, 1].affirmAllerRetour(op.sinonI32Hex)
+[0, 1].affirmAllerRetour(op.sinonU64Hex)
+[0, 1].affirmAllerRetour(op.sinonI64Hex)
+
+[0, 1].affirmAllerRetour(op.sinonU32Oct)
+
+// floats
+[0.0, 1.0].affirmAllerRetour(op.sinonF32)
+[0.0, 1.0].affirmAllerRetour(op.sinonF64)
+
+// enums
+[.un, .deux, .trois].affirmAllerRetour(op.sinonEnum)
+
+// Testing defaulting properties in record types.
+let defaultes = OptionneurDictionnaire()
+let explicite = OptionneurDictionnaire(
+    i8Var: Int8(-8),
+    u8Var: UInt8(8),
+    i16Var: Int16(-16),
+    u16Var: UInt16(0x10),
+    i32Var: -32,
+    u32Var: UInt32(32),
+    i64Var: Int64(-64),
+    u64Var: UInt64(64),
+    floatVar: Float(4.0),
+    doubleVar: Double(8.0),
+    booleanVar: true,
+    stringVar: "default",
+    listVar: [],
+    enumerationVar: .deux,
+    dictionnaireVar: nil
+)  
+
+// …and makes sure they travel across and back the FFI.
+assert(defaultes == explicite)
+[defaultes].affirmAllerRetour(rt.identiqueOptionneurDictionnaire)
--- a/third_party/rust/uniffi-example-rondpoint/tests/test_generated_bindings.rs
+++ b/third_party/rust/uniffi-example-rondpoint/tests/test_generated_bindings.rs
@ -0,0 +1,9 @@
+uniffi_macros::build_foreign_language_testcases!(
+    ["src/rondpoint.udl",],
+    [
+        "tests/bindings/test_rondpoint.kts",
+        "tests/bindings/test_rondpoint.swift",
+        "tests/bindings/test_rondpoint.py",
+        "tests/bindings/test_rondpoint.rb",
+    ]
+);
--- a/third_party/rust/uniffi-example-sprites/.cargo-checksum.json
+++ b/third_party/rust/uniffi-example-sprites/.cargo-checksum.json
@ -0,0 +1 @@
+{"files":{"Cargo.toml":"b288fc6b1e909cffdb5171a247f268884a2483d9f97f1a24a679681fb418bd8d","build.rs":"d36e4ff477007611d216e60998d6d8a51b33895bb95159e3d7732e2b8cbc1783","src/lib.rs":"79ae1ea584942b25c108a26df79a781a63d66f8fb37c4dacfc04d180752effcb","src/sprites.udl":"bfd35f04ba0549301189dfb8fc45b0f39bad00956c324f33be0e845fb7ff78aa","tests/bindings/test_sprites.kts":"06ed115325f37ce59ed6f33e2d651cd2aa352fddcc644580f62a6da6ca075844","tests/bindings/test_sprites.py":"2e6ce838cfb387586257703c3500062438e840dd7ae57d185cdc244dc0745b8f","tests/bindings/test_sprites.rb":"6289a1833c7c8f4583ee4f0488d680de2ee46cfb203095a9b66d7234e2f07d53","tests/bindings/test_sprites.swift":"b2c0a6f4d5edfd7de7c2ba77b838865ffda153a6f364f273456175192d3e6e00","tests/test_generated_bindings.rs":"920c532011c8a6c20bdb1f39c50ef7a2803729a62a1bd425d81e40300958778a"},"package":null}
--- a/third_party/rust/uniffi-example-sprites/Cargo.toml
+++ b/third_party/rust/uniffi-example-sprites/Cargo.toml
@ -0,0 +1,18 @@
+[package]
+name = "uniffi-example-sprites"
+edition = "2021"
+version = "0.18.0"
+authors = ["Firefox Sync Team <sync-team@mozilla.com>"]
+license = "MPL-2.0"
+publish = false
+
+[lib]
+crate-type = ["lib", "cdylib"]
+name = "uniffi_sprites"
+
+[dependencies]
+uniffi_macros = {path = "../../uniffi_macros"}
+uniffi = {path = "../../uniffi", features=["builtin-bindgen"]}
+
+[build-dependencies]
+uniffi_build = {path = "../../uniffi_build", features=["builtin-bindgen"]}
--- a/third_party/rust/uniffi-example-sprites/build.rs
+++ b/third_party/rust/uniffi-example-sprites/build.rs
@ -0,0 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+fn main() {
+    uniffi_build::generate_scaffolding("./src/sprites.udl").unwrap();
+}
--- a/third_party/rust/uniffi-example-sprites/src/lib.rs
+++ b/third_party/rust/uniffi-example-sprites/src/lib.rs
@ -0,0 +1,65 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use std::sync::RwLock;
+
+// A point in two-dimensional space.
+#[derive(Debug, Clone)]
+pub struct Point {
+    x: f64,
+    y: f64,
+}
+
+// A magnitude and direction in two-dimensional space.
+// For simplicity we represent this as a point relative to the origin.
+#[derive(Debug, Clone)]
+pub struct Vector {
+    dx: f64,
+    dy: f64,
+}
+
+// Move from the given Point, according to the given Vector.
+pub fn translate(p: &Point, v: Vector) -> Point {
+    Point {
+        x: p.x + v.dx,
+        y: p.y + v.dy,
+    }
+}
+
+// An entity in our imaginary world, which occupies a position in space
+// and which can move about over time.
+#[derive(Debug)]
+pub struct Sprite {
+    // We must use interior mutability for managing mutable state, hence the `RwLock`.
+    current_position: RwLock<Point>,
+}
+
+impl Sprite {
+    fn new(initial_position: Option<Point>) -> Sprite {
+        Sprite {
+            current_position: RwLock::new(initial_position.unwrap_or(Point { x: 0.0, y: 0.0 })),
+        }
+    }
+
+    fn new_relative_to(reference: Point, direction: Vector) -> Sprite {
+        Sprite {
+            current_position: RwLock::new(translate(&reference, direction)),
+        }
+    }
+
+    fn get_position(&self) -> Point {
+        self.current_position.read().unwrap().clone()
+    }
+
+    fn move_to(&self, position: Point) {
+        *self.current_position.write().unwrap() = position;
+    }
+
+    fn move_by(&self, direction: Vector) {
+        let mut current_position = self.current_position.write().unwrap();
+        *current_position = translate(&*current_position, direction)
+    }
+}
+
+include!(concat!(env!("OUT_DIR"), "/sprites.uniffi.rs"));
--- a/third_party/rust/uniffi-example-sprites/src/sprites.udl
+++ b/third_party/rust/uniffi-example-sprites/src/sprites.udl
@ -0,0 +1,22 @@
+
+namespace sprites {
+  Point translate([ByRef] Point position, Vector direction);
+};
+
+dictionary Point {
+  double x;
+  double y;
+};
+
+dictionary Vector {
+  double dx;
+  double dy;
+};
+
+interface Sprite {
+  constructor(Point? initial_position);
+  [Name=new_relative_to] constructor(Point reference, Vector direction);
+  Point get_position();
+  void move_to(Point position);
+  void move_by(Vector direction);
+};
--- a/third_party/rust/uniffi-example-sprites/tests/bindings/test_sprites.kts
+++ b/third_party/rust/uniffi-example-sprites/tests/bindings/test_sprites.kts
@ -0,0 +1,25 @@
+import uniffi.sprites.*;
+
+val sempty = Sprite(null)
+assert( sempty.getPosition() == Point(0.0, 0.0) )
+
+val s = Sprite(Point(0.0, 1.0))
+assert( s.getPosition() == Point(0.0, 1.0) )
+
+s.moveTo(Point(1.0, 2.0))
+assert( s.getPosition() == Point(1.0, 2.0) )
+
+s.moveBy(Vector(-4.0, 2.0))
+assert( s.getPosition() == Point(-3.0, 4.0) )
+
+s.destroy()
+try {
+    s.moveBy(Vector(0.0, 0.0))
+    assert(false) { "Should not be able to call anything after `destroy`" }
+} catch(e: IllegalStateException) {
+    assert(true)
+}
+
+val srel = Sprite.newRelativeTo(Point(0.0, 1.0), Vector(1.0, 1.5))
+assert( srel.getPosition() == Point(1.0, 2.5) )
+
--- a/third_party/rust/uniffi-example-sprites/tests/bindings/test_sprites.py
+++ b/third_party/rust/uniffi-example-sprites/tests/bindings/test_sprites.py
@ -0,0 +1,17 @@
+from sprites import *
+
+sempty = Sprite(None)
+assert sempty.get_position() == Point(0, 0)
+
+s = Sprite(Point(0, 1))
+assert s.get_position() == Point(0, 1)
+
+s.move_to(Point(1, 2))
+assert s.get_position() == Point(1, 2)
+
+s.move_by(Vector(-4, 2))
+assert s.get_position() == Point(-3, 4)
+
+srel = Sprite.new_relative_to(Point(0, 1), Vector(1, 1.5))
+assert srel.get_position() == Point(1, 2.5)
+
--- a/third_party/rust/uniffi-example-sprites/tests/bindings/test_sprites.rb
+++ b/third_party/rust/uniffi-example-sprites/tests/bindings/test_sprites.rb
@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require 'test/unit'
+require 'sprites'
+
+include Test::Unit::Assertions
+include Sprites
+
+sempty = Sprite.new(nil)
+assert_equal sempty.get_position, Point.new(0, 0)
+
+s = Sprite.new(Point.new(0, 1))
+assert_equal s.get_position, Point.new(0, 1)
+
+s.move_to(Point.new(1, 2))
+assert_equal s.get_position, Point.new(1, 2)
+
+s.move_by(Vector.new(-4, 2))
+assert_equal s.get_position, Point.new(-3, 4)
+
+srel = Sprite.new_relative_to(Point.new(0, 1), Vector.new(1, 1.5))
+assert_equal srel.get_position, Point.new(1, 2.5)
--- a/third_party/rust/uniffi-example-sprites/tests/bindings/test_sprites.swift
+++ b/third_party/rust/uniffi-example-sprites/tests/bindings/test_sprites.swift
@ -0,0 +1,16 @@
+import sprites
+
+let sempty = Sprite(initialPosition: nil)
+assert( sempty.getPosition() == Point(x: 0, y: 0))
+
+let s = Sprite(initialPosition: Point(x: 0, y: 1))
+assert( s.getPosition() == Point(x: 0, y: 1))
+
+s.moveTo(position: Point(x: 1.0, y: 2.0))
+assert( s.getPosition() == Point(x: 1, y: 2))
+
+s.moveBy(direction: Vector(dx: -4, dy: 2))
+assert( s.getPosition() == Point(x: -3, y: 4))
+
+let srel = Sprite.newRelativeTo(reference: Point(x: 0.0, y: 1.0), direction: Vector(dx: 1, dy: 1.5))
+assert( srel.getPosition() == Point(x: 1.0, y: 2.5) )
--- a/third_party/rust/uniffi-example-sprites/tests/test_generated_bindings.rs
+++ b/third_party/rust/uniffi-example-sprites/tests/test_generated_bindings.rs
@ -0,0 +1,9 @@
+uniffi_macros::build_foreign_language_testcases!(
+    ["src/sprites.udl",],
+    [
+        "tests/bindings/test_sprites.py",
+        "tests/bindings/test_sprites.rb",
+        "tests/bindings/test_sprites.kts",
+        "tests/bindings/test_sprites.swift",
+    ]
+);
--- a/third_party/rust/uniffi-example-todolist/.cargo-checksum.json
+++ b/third_party/rust/uniffi-example-todolist/.cargo-checksum.json
@ -0,0 +1 @@
+{"files":{"Cargo.toml":"4f4fc40bccf4ca5b105ea2abdbcdc6758ba7271d7d4ceb1e8ed45e3de227c2a6","build.rs":"ca26833c671cfe14a8275c276c197ab228cb1639b34cae31bb3805221ecc1245","src/lib.rs":"6a38904924681aed26b74876ad0480fedf8e8b2640cd2b04531a55aba8fc5592","src/todolist.udl":"1f8a24049c2340b9184e95facfc191ecdcb91541729ae7f20b4625d67685f13c","tests/bindings/test_todolist.kts":"f3d29b48e0193563fc4f131d91ea697f758174dcdb80ea554f233949e575bf55","tests/bindings/test_todolist.py":"f7430af9347df0daa954d38bc2203ce400affbb9a53fced4bb67a6796afa0664","tests/bindings/test_todolist.rb":"6524b5271a9cc0e2d78ca9f86ccb6973889926688a0843b4505a4f62d48f6dcb","tests/bindings/test_todolist.swift":"d1911b85fe0c8c0b42e5421b5af5d7359c9a65bba477d23560eb4b0f52e80662","tests/test_generated_bindings.rs":"25108de454213659c3eacd643a24c49099757a6b6da501fdb50874f574bd30c5"},"package":null}
--- a/third_party/rust/uniffi-example-todolist/Cargo.toml
+++ b/third_party/rust/uniffi-example-todolist/Cargo.toml
@ -0,0 +1,20 @@
+[package]
+name = "uniffi-example-todolist"
+edition = "2021"
+version = "0.18.0"
+authors = ["Firefox Sync Team <sync-team@mozilla.com>"]
+license = "MPL-2.0"
+publish = false
+
+[lib]
+crate-type = ["lib", "cdylib"]
+name = "uniffi_todolist"
+
+[dependencies]
+uniffi_macros = {path = "../../uniffi_macros"}
+uniffi = {path = "../../uniffi", features=["builtin-bindgen"]}
+thiserror = "1.0"
+lazy_static = "1.4"
+
+[build-dependencies]
+uniffi_build = {path = "../../uniffi_build", features=["builtin-bindgen"]}
--- a/third_party/rust/uniffi-example-todolist/build.rs
+++ b/third_party/rust/uniffi-example-todolist/build.rs
@ -0,0 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+fn main() {
+    uniffi_build::generate_scaffolding("./src/todolist.udl").unwrap();
+}
--- a/third_party/rust/uniffi-example-todolist/src/lib.rs
+++ b/third_party/rust/uniffi-example-todolist/src/lib.rs
@ -0,0 +1,150 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use std::sync::{Arc, RwLock};
+
+#[derive(Debug, Clone)]
+pub struct TodoEntry {
+    text: String,
+}
+
+lazy_static::lazy_static! {
+    // There is a single "default" TodoList that can be shared
+    // by all consumers of this component. Depending on requirements,
+    // a real app might like to use a `Weak<>` rather than an `Arc<>`
+    // here to reduce the risk of circular references.
+    static ref DEFAULT_LIST: RwLock<Option<Arc<TodoList>>> = RwLock::new(None);
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum TodoError {
+    #[error("The todo does not exist!")]
+    TodoDoesNotExist,
+    #[error("The todolist is empty!")]
+    EmptyTodoList,
+    #[error("That todo already exists!")]
+    DuplicateTodo,
+    #[error("Empty String error!: {0}")]
+    EmptyString(String),
+    #[error("I am a delegated Error: {0}")]
+    DeligatedError(#[from] std::io::Error),
+}
+
+/// Get a reference to the global default TodoList, if set.
+///
+fn get_default_list() -> Option<Arc<TodoList>> {
+    DEFAULT_LIST.read().unwrap().clone()
+}
+
+/// Set the global default TodoList.
+///
+/// This will silently drop any previously set value.
+///
+fn set_default_list(list: Arc<TodoList>) {
+    *DEFAULT_LIST.write().unwrap() = Some(list);
+}
+
+/// Create a new TodoEntry from the given string.
+///
+fn create_entry_with<S: Into<String>>(item: S) -> Result<TodoEntry> {
+    let text = item.into();
+    if text.is_empty() {
+        return Err(TodoError::EmptyString(
+            "Cannot add empty string as entry".to_string(),
+        ));
+    }
+    Ok(TodoEntry { text })
+}
+
+type Result<T, E = TodoError> = std::result::Result<T, E>;
+
+// A simple Todolist.
+// UniFFI requires that we use interior mutability for managing mutable state, so we wrap our `Vec` in a RwLock.
+// (A Mutex would also work, but a RwLock is more appropriate for this use-case, so we use it).
+#[derive(Debug)]
+pub struct TodoList {
+    items: RwLock<Vec<String>>,
+}
+
+impl TodoList {
+    fn new() -> Self {
+        Self {
+            items: RwLock::new(Vec::new()),
+        }
+    }
+
+    fn add_item<S: Into<String>>(&self, item: S) -> Result<()> {
+        let item = item.into();
+        if item.is_empty() {
+            return Err(TodoError::EmptyString(
+                "Cannot add empty string as item".to_string(),
+            ));
+        }
+        let mut items = self.items.write().unwrap();
+        if items.contains(&item) {
+            return Err(TodoError::DuplicateTodo);
+        }
+        items.push(item);
+        Ok(())
+    }
+
+    fn get_last(&self) -> Result<String> {
+        let items = self.items.read().unwrap();
+        items.last().cloned().ok_or(TodoError::EmptyTodoList)
+    }
+
+    fn get_first(&self) -> Result<String> {
+        let items = self.items.read().unwrap();
+        items.first().cloned().ok_or(TodoError::EmptyTodoList)
+    }
+
+    fn add_entries(&self, entries: Vec<TodoEntry>) {
+        let mut items = self.items.write().unwrap();
+        items.extend(entries.into_iter().map(|e| e.text))
+    }
+
+    fn add_entry(&self, entry: TodoEntry) -> Result<()> {
+        self.add_item(entry.text)
+    }
+
+    fn add_items<S: Into<String>>(&self, items: Vec<S>) {
+        let mut my_items = self.items.write().unwrap();
+        my_items.extend(items.into_iter().map(Into::into))
+    }
+
+    fn get_items(&self) -> Vec<String> {
+        let items = self.items.read().unwrap();
+        items.clone()
+    }
+
+    fn get_entries(&self) -> Vec<TodoEntry> {
+        let items = self.items.read().unwrap();
+        items
+            .iter()
+            .map(|text| TodoEntry { text: text.clone() })
+            .collect()
+    }
+
+    fn get_last_entry(&self) -> Result<TodoEntry> {
+        let text = self.get_last()?;
+        Ok(TodoEntry { text })
+    }
+
+    fn clear_item<S: Into<String>>(&self, item: S) -> Result<()> {
+        let item = item.into();
+        let mut items = self.items.write().unwrap();
+        let idx = items
+            .iter()
+            .position(|s| s == &item)
+            .ok_or(TodoError::TodoDoesNotExist)?;
+        items.remove(idx);
+        Ok(())
+    }
+
+    fn make_default(self: Arc<Self>) {
+        set_default_list(self);
+    }
+}
+
+include!(concat!(env!("OUT_DIR"), "/todolist.uniffi.rs"));
--- a/third_party/rust/uniffi-example-todolist/src/todolist.udl
+++ b/third_party/rust/uniffi-example-todolist/src/todolist.udl
@ -0,0 +1,38 @@
+namespace todolist {
+    TodoList? get_default_list();
+    undefined set_default_list(TodoList list);
+
+    [Throws=TodoError]
+    TodoEntry create_entry_with(string todo);
+};
+
+dictionary TodoEntry {
+    string text;
+};
+
+[Error]
+enum TodoError {
+    "TodoDoesNotExist", "EmptyTodoList", "DuplicateTodo", "EmptyString", "DeligatedError"
+};
+
+interface TodoList {
+    constructor();
+    [Throws=TodoError]
+    void add_item(string todo);
+    [Throws=TodoError]
+    void add_entry(TodoEntry entry);
+    sequence<TodoEntry> get_entries();
+    sequence<string> get_items();
+    void add_entries(sequence<TodoEntry> entries);
+    void add_items(sequence<string> items);
+    [Throws=TodoError]
+    TodoEntry get_last_entry();
+    [Throws=TodoError]
+    string get_last();
+    [Throws=TodoError]
+    string get_first();
+    [Throws=TodoError]
+    void clear_item(string todo);
+    [Self=ByArc]
+    undefined make_default();
+};
--- a/third_party/rust/uniffi-example-todolist/tests/bindings/test_todolist.kts
+++ b/third_party/rust/uniffi-example-todolist/tests/bindings/test_todolist.kts
@ -0,0 +1,83 @@
+import uniffi.todolist.*
+
+val todo = TodoList()
+
+// This throws an exception:
+try {
+    todo.getLast()
+    throw RuntimeException("Should have thrown a TodoError!")
+} catch (e: TodoException.EmptyTodoList) {
+    // It's okay, we don't have any items yet!
+}
+
+try {
+    createEntryWith("")
+    throw RuntimeException("Should have thrown a TodoError!")
+} catch (e: TodoException) {
+    // It's okay, the string was empty!
+    assert(e is TodoException.EmptyString)
+    assert(e !is TodoException.EmptyTodoList)
+}
+
+todo.addItem("Write strings support")
+
+assert(todo.getLast() == "Write strings support")
+
+todo.addItem("Write tests for strings support")
+
+assert(todo.getLast() == "Write tests for strings support")
+
+val entry = createEntryWith("Write bindings for strings as record members")
+
+todo.addEntry(entry)
+assert(todo.getLast() == "Write bindings for strings as record members")
+assert(todo.getLastEntry().text == "Write bindings for strings as record members")
+
+todo.addItem("Test Ünicode hàndling without an entry can't believe I didn't test this at first 🤣")
+assert(todo.getLast() == "Test Ünicode hàndling without an entry can't believe I didn't test this at first 🤣")
+
+val entry2 = TodoEntry("Test Ünicode hàndling in an entry can't believe I didn't test this at first 🤣")
+todo.addEntry(entry2)
+assert(todo.getLastEntry().text == "Test Ünicode hàndling in an entry can't believe I didn't test this at first 🤣")
+
+assert(todo.getEntries().size == 5)
+
+todo.addEntries(listOf(TodoEntry("foo"), TodoEntry("bar")))
+assert(todo.getEntries().size == 7)
+assert(todo.getLastEntry().text == "bar")
+
+todo.addItems(listOf("bobo", "fofo"))
+assert(todo.getItems().size == 9)
+assert(todo.getItems()[7] == "bobo")
+
+assert(getDefaultList() == null)
+
+// Note that each individual object instance needs to be explicitly destroyed,
+// either by using the `.use` helper or explicitly calling its `.destroy` method.
+// Failure to do so will leak the underlying Rust object.
+TodoList().use { todo2 ->
+    setDefaultList(todo)
+    getDefaultList()!!.use { default ->
+        assert(todo.getEntries() == default.getEntries())
+        assert(todo2.getEntries() != default.getEntries())
+    }
+
+    todo2.makeDefault()
+    getDefaultList()!!.use { default ->
+        assert(todo.getEntries() != default.getEntries())
+        assert(todo2.getEntries() == default.getEntries())
+    }
+
+    todo.addItem("Test liveness after being demoted from default")
+    assert(todo.getLast() == "Test liveness after being demoted from default")
+
+    todo2.addItem("Test shared state through local vs default reference")
+    getDefaultList()!!.use { default ->
+        assert(default.getLast() == "Test shared state through local vs default reference")
+    }
+}
+
+// Ensure the kotlin version of deinit doesn't crash, and is idempotent.
+todo.destroy()
+todo.destroy()
+
--- a/third_party/rust/uniffi-example-todolist/tests/bindings/test_todolist.py
+++ b/third_party/rust/uniffi-example-todolist/tests/bindings/test_todolist.py
@ -0,0 +1,44 @@
+from todolist import *
+
+todo = TodoList()
+
+entry = TodoEntry("Write bindings for strings in records")
+
+todo.add_item("Write python bindings")
+
+assert(todo.get_last() == "Write python bindings")
+
+todo.add_item("Write tests for bindings")
+
+assert(todo.get_last() == "Write tests for bindings")
+
+todo.add_entry(entry)
+
+assert(todo.get_last() == "Write bindings for strings in records")
+assert(todo.get_last_entry().text == "Write bindings for strings in records")
+
+todo.add_item("Test Ünicode hàndling without an entry can't believe I didn't test this at first 🤣")
+assert(todo.get_last() == "Test Ünicode hàndling without an entry can't believe I didn't test this at first 🤣")
+
+entry2 = TodoEntry("Test Ünicode hàndling in an entry can't believe I didn't test this at first 🤣")
+todo.add_entry(entry2)
+assert(todo.get_last_entry().text == "Test Ünicode hàndling in an entry can't believe I didn't test this at first 🤣")
+
+todo2 = TodoList()
+assert(todo != todo2)
+assert(todo is not todo2)
+
+assert(get_default_list() is None)
+
+set_default_list(todo)
+assert(todo.get_items() == get_default_list().get_items())
+
+todo2.make_default()
+assert(todo2.get_items() == get_default_list().get_items())
+
+todo.add_item("Test liveness after being demoted from default")
+assert(todo.get_last() == "Test liveness after being demoted from default")
+
+todo2.add_item("Test shared state through local vs default reference")
+assert(get_default_list().get_last() == "Test shared state through local vs default reference")
+
--- a/third_party/rust/uniffi-example-todolist/tests/bindings/test_todolist.rb
+++ b/third_party/rust/uniffi-example-todolist/tests/bindings/test_todolist.rb
@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require 'test/unit'
+require 'todolist'
+
+include Test::Unit::Assertions
+include Todolist
+
+todo = TodoList.new
+entry = TodoEntry.new 'Write bindings for strings in records'
+
+todo.add_item('Write ruby bindings')
+
+assert_equal todo.get_last, 'Write ruby bindings'
+
+todo.add_item('Write tests for bindings')
+
+assert_equal todo.get_last, 'Write tests for bindings'
+
+todo.add_entry(entry)
+
+assert_equal todo.get_last, 'Write bindings for strings in records'
+assert_equal todo.get_last_entry.text, 'Write bindings for strings in records'
+
+todo.add_item("Test Ünicode hàndling without an entry can't believe I didn't test this at first 🤣")
+assert_equal todo.get_last, "Test Ünicode hàndling without an entry can't believe I didn't test this at first 🤣"
+
+entry2 = TodoEntry.new("Test Ünicode hàndling in an entry can't believe I didn't test this at first 🤣")
+todo.add_entry(entry2)
+assert_equal todo.get_last_entry.text, "Test Ünicode hàndling in an entry can't believe I didn't test this at first 🤣"
+
+todo2 = TodoList.new
+assert todo2.get_items != todo.get_items
+
+assert Todolist.get_default_list == nil
+
+Todolist.set_default_list todo
+assert todo.get_items == Todolist.get_default_list.get_items
+
+todo2.make_default
+assert todo2.get_items == Todolist.get_default_list.get_items
+
+todo.add_item "Test liveness after being demoted from default"
+assert todo.get_last == "Test liveness after being demoted from default"
+
+todo2.add_item "Test shared state through local vs default reference"
+assert Todolist.get_default_list.get_last == "Test shared state through local vs default reference"
--- a/third_party/rust/uniffi-example-todolist/tests/bindings/test_todolist.swift
+++ b/third_party/rust/uniffi-example-todolist/tests/bindings/test_todolist.swift
@ -0,0 +1,69 @@
+import todolist
+
+
+let todo = TodoList()
+do {
+    let _ = try todo.getLast()
+    fatalError("Should have thrown an EmptyTodoList error!")
+} catch TodoError.EmptyTodoList{
+    //It's okay! There are not todos!
+}
+try! todo.addItem(todo: "Write swift bindings")
+assert( try! todo.getLast() == "Write swift bindings")
+
+try! todo.addItem(todo: "Write tests for bindings")
+assert(try! todo.getLast() == "Write tests for bindings")
+
+let entry = TodoEntry(text: "Write bindings for strings as record members")
+try! todo.addEntry(entry: entry)
+assert(try! todo.getLast() == "Write bindings for strings as record members")
+
+try! todo.addItem(todo: "Test Ünicode hàndling without an entry can't believe I didn't test this at first 🤣")
+assert(try! todo.getLast() == "Test Ünicode hàndling without an entry can't believe I didn't test this at first 🤣")
+
+do {
+    let _ = try createEntryWith(todo: "")
+    fatalError("Should have thrown an EmptyString error!")
+} catch TodoError.EmptyString {
+    // It's okay! It was an empty string
+}
+
+let entry2 = TodoEntry(text: "Test Ünicode hàndling in an entry can't believe I didn't test this at first 🤣")
+try! todo.addEntry(entry: entry2)
+assert(try! todo.getLastEntry() == entry2)
+
+assert(todo.getEntries().count == 5)
+
+todo.addEntries(entries: [TodoEntry(text: "foo"), TodoEntry(text: "bar")])
+assert(todo.getEntries().count == 7)
+assert(todo.getItems().count == 7)
+assert(try! todo.getLast() == "bar")
+
+todo.addItems(items: ["bobo", "fofo"])
+assert(todo.getItems().count == 9)
+assert(todo.getItems()[7] == "bobo")
+
+// Ensure deinit doesn't crash.
+for _ in 0..<10 {
+    let list = TodoList()
+    try! list.addItem(todo: "todo")
+}
+
+let todo2 = TodoList()
+
+assert(getDefaultList() == nil)
+
+setDefaultList(list: todo)
+assert(todo.getItems() == getDefaultList()!.getItems())
+assert(todo2.getItems() != getDefaultList()!.getItems())
+
+todo2.makeDefault()
+assert(todo.getItems() != getDefaultList()!.getItems())
+assert(todo2.getItems() == getDefaultList()!.getItems())
+
+try! todo.addItem(todo: "Test liveness after being demoted from default")
+assert(try! todo.getLast() == "Test liveness after being demoted from default")
+
+try! todo2.addItem(todo: "Test shared state through local vs default reference")
+assert(try! getDefaultList()!.getLast() == "Test shared state through local vs default reference")
+
--- a/third_party/rust/uniffi-example-todolist/tests/test_generated_bindings.rs
+++ b/third_party/rust/uniffi-example-todolist/tests/test_generated_bindings.rs
@ -0,0 +1,9 @@
+uniffi_macros::build_foreign_language_testcases!(
+    ["src/todolist.udl",],
+    [
+        "tests/bindings/test_todolist.kts",
+        "tests/bindings/test_todolist.swift",
+        "tests/bindings/test_todolist.rb",
+        "tests/bindings/test_todolist.py"
+    ]
+);
--- a/toolkit/components/uniffi-bindgen-gecko-js/Cargo.toml
+++ b/toolkit/components/uniffi-bindgen-gecko-js/Cargo.toml
@ -13,7 +13,7 @@ askama = { version = "0.11", default-features = false, features = ["config"] }
 clap = { version = "3.1", features = ["std", "derive"] }
 extend = "1.1"
 heck = "0.4"
-uniffi_bindgen = "0.18"
+uniffi_bindgen = "0.19"
 serde = "1"
 toml = "0.5"
 camino = "1.0.8"
--- a/toolkit/library/rust/gkrust-features.mozbuild
+++ b/toolkit/library/rust/gkrust-features.mozbuild
@ -74,6 +74,8 @@ if CONFIG["MOZ_CRASHREPORTER"] and CONFIG['MOZ_OXIDIZED_BREAKPAD']:
 if CONFIG["MOZ_WEBMIDI_MIDIR_IMPL"]:
    gkrust_features += ['webmidi_midir_impl']

+if CONFIG["MOZ_UNIFFI_FIXTURES"]:
+    gkrust_features += ['uniffi_fixtures']

 # This must remain last.
 gkrust_features = ["gkrust-shared/%s" % f for f in gkrust_features]
--- a/toolkit/library/rust/shared/Cargo.toml
+++ b/toolkit/library/rust/shared/Cargo.toml
@ -75,6 +75,11 @@ origin-trials-ffi = { path = "../../../../dom/origin-trials/ffi" }
 jog = { path = "../../../components/glean/bindings/jog" }
 dap_ffi = { path = "../../../components/telemetry/dap/ffi" }
 data-encoding-ffi = { path = "../../../../dom/fs/parent/rust/data-encoding-ffi" }
+uniffi-example-arithmetic = { git = "https://github.com/mozilla/uniffi-rs.git", rev = "bb2039f077a29dba0879372a67e764e6ace8e33f", optional = true }
+uniffi-example-geometry = { git = "https://github.com/mozilla/uniffi-rs.git", rev = "bb2039f077a29dba0879372a67e764e6ace8e33f", optional = true }
+uniffi-example-rondpoint = { git = "https://github.com/mozilla/uniffi-rs.git", rev = "bb2039f077a29dba0879372a67e764e6ace8e33f", optional = true }
+uniffi-example-sprites = { git = "https://github.com/mozilla/uniffi-rs.git", rev = "bb2039f077a29dba0879372a67e764e6ace8e33f", optional = true }
+uniffi-example-todolist = { git = "https://github.com/mozilla/uniffi-rs.git", rev = "bb2039f077a29dba0879372a67e764e6ace8e33f", optional = true }

 # Note: `modern_sqlite` means rusqlite's bindings file be for a sqlite with
 # version less than or equal to what we link to. This isn't a problem because we
@ -127,6 +132,10 @@ glean_with_gecko = ["fog_control/with_gecko", "jog/with_gecko"]
 oxidized_breakpad = ["rust_minidump_writer_linux"]
 with_dbus = ["audio_thread_priority/with_dbus"]
 thread_sanitizer = ["xpcom/thread_sanitizer"]
+uniffi_fixtures = [
+    "uniffi-example-arithmetic", "uniffi-example-geometry", "uniffi-example-rondpoint", "uniffi-example-sprites",
+    "uniffi-example-todolist",
+]
 webmidi_midir_impl = ["midir_impl"]

 [lib]
--- a/toolkit/library/rust/shared/lib.rs
+++ b/toolkit/library/rust/shared/lib.rs
@ -99,6 +99,21 @@ extern crate dap_ffi;

 extern crate data_encoding_ffi;

+#[cfg(feature = "uniffi_fixtures")]
+mod uniffi_fixtures {
+    extern crate arithmetical;
+    extern crate uniffi_geometry;
+    extern crate uniffi_rondpoint;
+    extern crate uniffi_sprites;
+    extern crate uniffi_todolist;
+
+    arithmetical::uniffi_reexport_scaffolding!();
+    uniffi_geometry::uniffi_reexport_scaffolding!();
+    uniffi_rondpoint::uniffi_reexport_scaffolding!();
+    uniffi_sprites::uniffi_reexport_scaffolding!();
+    uniffi_todolist::uniffi_reexport_scaffolding!();
+}
+
 extern crate log;
 use log::info;

--- a/toolkit/moz.configure
+++ b/toolkit/moz.configure
@ -3202,6 +3202,19 @@ def disable_smart_cards(build_project):
 set_config("MOZ_NO_SMART_CARDS", True, when=disable_smart_cards)
 set_define("MOZ_NO_SMART_CARDS", True, when=disable_smart_cards)

+# Enable UniFFI fixtures
+# ==============================================================
+# These are used to test the uniffi-bindgen-gecko-js code generation.  They
+# should not be enabled in release builds.
+
+option(
+    "--enable-uniffi-fixtures",
+    help="Enable UniFFI Fixtures/Examples",
+)
+
+
+set_config("MOZ_UNIFFI_FIXTURES", True, when="--enable-uniffi-fixtures")
+
 # Checks for library functions
 # ==============================================================
 with only_when(compile_environment & depends(target.os)(lambda os: os != "WINNT")):
				`@ -0,0 +1 @@`
				{"files":{"CHANGELOG.md":"910cd2057d356b18cd4f21791bc23956734a83b0f58701ec0d0d03405f5c21df","Cargo.toml":"928b8b97607b3589b85a6d4d00fb1cf64b78bee6354c303d8f49fbfa2ca5bdae","LICENSE":"db0efd0bb80126f32214f478434536d07d86a30658fb209d8b543b7261492a2b","README.md":"0872b2b15ec22732a09b121a31cdd8f8cfc80566f671566e4a7fb6b52a742a2e","deny.toml":"60448e9313f1883a7adf30713fcca789c454e77228105926024ce3abe9293100","rustfmt.toml":"9bbb759b3914c49c8060bcdeeb7786f4aec083d30bcfe236bbd48d8388d06103","src/lib.rs":"85bd23c064c78dcd141cb2fecca6fff2ee7e1dfb4cf19b74ab97ef30d51f6f03","tests/compile_fail/double_vis.rs":"524e8bc996f5a45de3d15f0c741d4f3414004e9c636c52de0f011785cc535109","tests/compile_fail/double_vis.stderr":"3748e67e6f41bd5624946ad7cdc4e2b30a9d0b5e76bc27c19ecc9d62da733978","tests/compile_fail/supertraits_are_actually_included.rs":"c03980316c4e71ceb7e80ab7011f00b6f1f8f89906670e9823267a4118f72853","tests/compile_fail/supertraits_are_actually_included.stderr":"835e79bb1bceb48e9db5f0a410c57af51c856e17917ef72f65e3ae2af79d97ec","tests/compile_pass/associated_constants.rs":"f3e56405650ddd31c33e932846553e88fe7181585e0f09a7414d50d521b0f103","tests/compile_pass/async_trait.rs":"9138801d67dbe20ed87fdb3f48bb968f0bfa11fe2d27414d5ea5ea7a6e44bb35","tests/compile_pass/changing_extension_trait_name.rs":"046e7a66151ce05c3515b4bea36be72f83b98f3bdb06fa6f065ad6fc373e19f2","tests/compile_pass/complex_trait_name.rs":"5a8c3588c26df07973739fbb85619d0de480cc8c992611dfc2dbcb9ab3c6e2b6","tests/compile_pass/double_ext_on_same_type.rs":"0e4d16fe9059f0325e4ad1337d53738876633b0533f9a2d4e9714ddada96eb4d","tests/compile_pass/extension_on_complex_types.rs":"88bdf979e1f399d7f9824165730b33884bc9c46347d246f8cc12e0e2039642a1","tests/compile_pass/generics.rs":"367f089e8010d1c98ccc975b03acb6cf03810793e1198105f75c006eafd52bb8","tests/compile_pass/hello_world.rs":"1961cfa634143974f0d64b26f817ac3148375faa5cf5864d63f0127d3af8099e","tests/compile_pass/issue_2.rs":"a14d5e2179b74ff71c5357e8a4f1a9ac228a711196edd40c12719565c8dfaa21","tests/compile_pass/more_than_one_extension.rs":"1d7486e4e9e4095d7e7f42aac878d836f021c49fbe26c31cb13fe6a0415a8558","tests/compile_pass/multiple_config.rs":"dc3b06e4fafbb7236b5bc49f9a5e9693241c07118da8886dd0752b895ff27425","tests/compile_pass/multiple_generic_params.rs":"2ac052ea7b818b6d45ee8070cf6ec18953419473f711375cafbe7283244b5743","tests/compile_pass/pub_impl.rs":"8dfcba21fbbc45efcf85b66fca2d187022569e72d4b10b57047eddda67a1725b","tests/compile_pass/ref_and_ref_mut.rs":"d1086a23809cbd8f87487677073238c3657a8a98fafc63a688eb9d622bf2eb11","tests/compile_pass/sized.rs":"baceaaabcf368b3c72e6d27fea72aadde11d97d9d153c35df5e2d89fb3da4e3e","tests/compile_pass/super_trait.rs":"07448e1fe2b9018125ccaabf7db1e2a244788519bb42117f8e437e48358eb2f0","tests/compile_pass/visibility_config.rs":"64846014a63327661fb250cdb726cce532ed82b1cea5cb83308526bcba22b4be"},"package":"5c5216e387a76eebaaf11f6d871ec8a4aae0b25f05456ee21f228e024b1b3610"}
				`@ -0,0 +1 @@`
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