Bug 1759555 - Part 1: Avoid using env! for includes in the mozbuild crate, r=glandium

This switches the code to instead use the generated source file, which is
discovered based on `OUT_DIR` so is easier for rust-analyzer to understand.

The configuration for rust-analyzer will be updated in the next part to
make sure that rust-analyzer is able to take advantage of these changes,
and produce better diagnostics.

Differential Revision: https://phabricator.services.mozilla.com/D153269

build/rust/mozbuild/generate_buildconfig.py

@@ -3,6 +3,8 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 import buildconfig
+import textwrap
+import string
 
 
 def generate_bool(name):
@@ -10,7 +12,55 @@ def generate_bool(name):
     return f"pub const {name}: bool = {'true' if value else 'false'};\n"
 
 
+def escape_rust_string(value):
+    """escape the string into a Rust literal"""
+    # This could be more generous, but we're only escaping paths with it.
+    unescaped = string.ascii_letters + string.digits + "/$+-_~ "
+    result = ""
+    for ch in str(value):
+        if ch in unescaped:
+            result += ch
+        elif ch == "\r":
+            result += "\\r"
+        elif ch == "\n":
+            result += "\\n"
+        elif ch == "\\":
+            result += "\\\\"
+        elif ch == '"':
+            result += '\\"'
+        else:
+            result += "\\u{%x}" % ord(ch)
+    return '"%s"' % result
+
+
 def generate(output):
+    # Write out a macro which can be used within `include!`-like methods to
+    # reference the topobjdir.
+    output.write(
+        textwrap.dedent(
+            f"""
+            /// Macro used to name a path in the objdir for use with macros like `include!`
+            #[macro_export]
+            macro_rules! objdir_path {{
+                ($path:literal) => {{ concat!({escape_rust_string(buildconfig.topobjdir + "/")}, $path) }}
+            }}
+
+            /// Macro used to name a path in the srcdir for use with macros like `include!`
+            #[macro_export]
+            macro_rules! srcdir_path {{
+                ($path:literal) => {{ concat!({escape_rust_string(buildconfig.topsrcdir + "/")}, $path) }}
+            }}
+
+            /// The objdir path for use in build scripts
+            pub const TOPOBJDIR: &str = {escape_rust_string(buildconfig.topobjdir)};
+            /// The srcdir path for use in build scripts
+            pub const TOPSRCDIR: &str = {escape_rust_string(buildconfig.topsrcdir)};
+
+            """
+        )
+    )
+
+    # Finally, write out some useful booleans from the buildconfig.
     output.write(generate_bool("MOZ_FOLD_LIBS"))
     output.write(generate_bool("NIGHTLY_BUILD"))
     output.write(generate_bool("RELEASE_OR_BETA"))

build/rust/mozbuild/lib.rs

@@ -3,38 +3,11 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use once_cell::sync::Lazy;
-use std::env;
-use std::path::PathBuf;
+use std::path::Path;
 
-pub static TOPOBJDIR: Lazy<PathBuf> = Lazy::new(|| {
-    let path = PathBuf::from(
-        env::var_os("MOZ_TOPOBJDIR").expect("MOZ_TOPOBJDIR must be set in the environment"),
-    );
-    assert!(
-        path.is_absolute() && path.is_dir(),
-        "MOZ_TOPOBJDIR must be an absolute directory, was: {}",
-        path.display()
-    );
-    path
-});
+pub static TOPOBJDIR: Lazy<&'static Path> = Lazy::new(|| Path::new(config::TOPOBJDIR));
 
-#[macro_export]
-macro_rules! objdir_path {
-    ($path:literal) => {
-        concat!(env!("MOZ_TOPOBJDIR"), "/", $path)
-    };
-}
-
-pub static TOPSRCDIR: Lazy<PathBuf> = Lazy::new(|| {
-    let path =
-        PathBuf::from(env::var_os("MOZ_SRC").expect("MOZ_SRC must be set in the environment"));
-    assert!(
-        path.is_absolute() && path.is_dir(),
-        "MOZ_SRC must be an absolute directory, was: {}",
-        path.display()
-    );
-    path
-});
+pub static TOPSRCDIR: Lazy<&'static Path> = Lazy::new(|| Path::new(config::TOPSRCDIR));
 
 pub mod config {
     include!(env!("BUILDCONFIG_RS"));

config/makefiles/rust.mk

@@ -219,7 +219,6 @@ export RUSTFLAGS
 export RUSTC
 export RUSTDOC
 export RUSTFMT
-export MOZ_SRC=$(topsrcdir)
 export LIBCLANG_PATH=$(MOZ_LIBCLANG_PATH)
 export CLANG_PATH=$(MOZ_CLANG_PATH)
 export PKG_CONFIG