build: patch rules_rust process_wrapper metadata handling

Co-authored-by: Codex <noreply@openai.com>

MODULE.bazel

@@ -42,6 +42,12 @@ bazel_dep(name = "rules_platform", version = "0.1.0")
 bazel_dep(name = "rules_rs", version = "0.0.40")
 
 rules_rust = use_extension("@rules_rs//rs/experimental:rules_rust.bzl", "rules_rust")
+rules_rust.patch(
+    patches = [
+        "//patches:rules_rs_process_wrapper_emit_metadata.patch",
+    ],
+    strip = 1,
+)
 use_repo(rules_rust, "rules_rust")
 
 toolchains = use_extension("@rules_rs//rs/experimental/toolchains:module_extension.bzl", "toolchains")

patches/rules_rs_process_wrapper_emit_metadata.patch

@@ -0,0 +1,18 @@
+diff --git a/util/process_wrapper/rustc.rs b/util/process_wrapper/rustc.rs
+index ddb82c9..69052ce 100644
+--- a/util/process_wrapper/rustc.rs
++++ b/util/process_wrapper/rustc.rs
+@@ -64,10 +64,12 @@ pub(crate) fn process_json(line: String, error_format: ErrorFormat) -> LineResult {
+     let parsed: JsonValue = line
+         .parse()
+         .map_err(|_| "error parsing rustc output as json".to_owned())?;
+     Ok(match parsed.try_into() {
++        Ok(RustcMessage::Emit(emit)) if emit == "metadata" => LineOutput::Terminate,
++        Ok(RustcMessage::Emit(_)) => LineOutput::Skip,
+         Ok(RustcMessage::Message(rendered)) => {
+             output_based_on_error_format(line, rendered, error_format)
+         }
+-        _ => LineOutput::Skip,
++        Err(()) => LineOutput::Skip,
+     })
+ }