Access to compiler artifact notifications messages

[pacak]

Problem

You can pass --json=artifacts to rustc and it will emit json messages like {"$message_type":"artifact","artifact":"/path/to/target/release/deps/libsample-fb5d74408737397e.rlib","emit":"link"} to stderr.

cargo then parses them and mostly ignores:

cargo/src/cargo/core/compiler/mod.rs

Lines 1803 to 1810 in a59aba1

	if let Ok(artifact) = serde_json::from_str::<ArtifactNotification>(compiler_message.get()) {
	trace!("found directive from rustc: `{}`", artifact.artifact);
	if artifact.artifact.ends_with(".rmeta") {
	debug!("looks like metadata finished early!");
	state.rmeta_produced();
	}
	return Ok(false);
	}

later emitting its own version:

cargo/src/cargo/core/compiler/mod.rs

Line 563 in a59aba1

destinations.push(src.clone());

I'm extending --json=artifacts in rustc to include files produced by --emit (rust-lang/rust#122597) to avoid doing fragile guesswork in cargo-show-asm, but right now this information won't be accessible when rustc is invoked via cargo.

Proposed Solution

cargo should collect this information when present and output it as part of its own notifications, including cases where rustc wasn't actually invoked if source files staid the same.

Notes

The alternative is for me to invoke rustc directly - fragile or to do nothing - currently I have to pass codegen-units=1 - potentially confusing behavior.

If approved - I can look into implementing required change myself.

[pacak]

FWIW rust-lang/rust#122597 is implemented and approved, awaiting on FCP to how exactly to get it merged.

[epage]

cargo show-asm is calling cargo rustc, passing --emit to rustc to render this information to users. They want to get the json messages for these emitted files so they can look up directly, rather than inferring.

For me, the main question is "why was the filtering done in the first place?"

The code in question was changed in

• 71d25f6
• 4617f78