зеркало из https://github.com/mozilla/uniffi-rs.git
10ac4b5541
Remote types present an issue because we can't implement FFI traits like
`Lower` and `Lift` on them directly. The workaround is to only
implement the FFI trait for the current crate. If another crate
wants to use that impl, we need to implement it again by forwarding to
the initial implementation.
Historically, UDL and proc-macros have approached this differently which
has lead to a lot of extra complexity and confusion. This change aligns
them on a common system: By default, we implement traits for all crates
(a "blanket impl"). However, users can opt-in to only implementing it
for the current crate ("a local impl`)
See the doc changes for a description of the new system.
This required a bunch of changes:
- UDL now creates a blanket impl by default. The [Remote] attribute can
be used to switch to a local impl.
- Proc-macros get the `#[remote]` attribute macro, which allows users to
create a local impl.
- Custom types now create a blanket impl by default. The `remote`
parameter can be used to create a local impl.
- Added the `remote_type!` macro to which handles the case where you
want to use a remote type and another crate has already created a
local impl. This creates a local impl for your crate by forwarding to
the other impl. Removed the `use_udl_*` macros, which were a kludge
for doing the same thing.
Added a motivating example where `anyhow::Error` is used as an error
type. Changed the error type bound to `Display + Debug` rather than
`Error`. For some reason `anyhow::Error` doesn't actually implement
error.
One feature that we've lost in defining callback/trait interfaces using
traits defined in a remote crate. I think this is okay because I doubt
anyone is using that feature.
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