--message-format=json should indicate which produced files are executables

[matklad]

Currently --message-format=json just dumps the list of files that was produced when compiling a project. Cargo doesn't have too much knowledge about what exactly is produced for which target and crate type, but it should indicate at least which artifact is an executable binary. This is important for IDEs, which at the moment have to implement ugly work-arounds to separate actual binaries from debuginfo, for example (see vadimcn/codelldb#104).

Some pointers to code:

• a struct representing JSON messages:

  cargo/src/cargo/util/machine_message.rs

  Line 30 in 3b14988

  pub struct Artifact<'a> {

• the place where we actually print the info:

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

  Lines 603 to 612 in 3b14988

  	if json_messages {
  	machine_message::emit(&machine_message::Artifact {
  	package_id: &package_id,
  	target: &target,
  	profile: &profile,
  	features,
  	filenames: destinations,
  	fresh,
  	});
  	}

• a struct which knows where the binaries are:

  cargo/src/cargo/core/compiler/compilation.rs

  Lines 17 to 21 in 3b14988

  	/// An array of all tests created during this compilation.
  	pub tests: Vec<(Package, TargetKind, String, PathBuf)>,
  	/// An array of all binaries created.
  	pub binaries: Vec<PathBuf>,

I think we could perhaps add an executable: Option<PathBuf> field to the CompilerArtifact?

[patriksvensson]

@matklad I can give this a try if no one else already started working on it.

[matklad]

Awesome! I think the relevant test for this is this one:

cargo/tests/testsuite/build.rs

Line 3994 in 6cd841f

fn compiler_json_error_format() {

[patriksvensson]

@matklad This is perhaps a stupid question, but how can I know which binary in Compilation.binaries is the executable (if any)?

[matklad]

@patriksvensson all binaries in binaries are executables, either tests, or real binaries with main and such. The logic for populating them is here:

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

Line 164 in 151f37c

self.compilation.binaries.push(bindst.clone());

I think that logic needs to be duplicated when emitting JSON messages.

[matklad]

Hm, I think that code is buggy actually! Filed #5474 about it. Would you like to tackle that first?

[patriksvensson]

@matklad Sure, I can try that one first.

[patriksvensson]

Will go ahead with this one now then.

[patriksvensson]

I've not given up on this. Simply just been a lot of work. Planning on continue working on the PR later today.

[dwijnand]

Hey @patriksvensson, how close to completion is https://github.com/patriksvensson/cargo/tree/feature/GH-5426 ? Are you still interested in working on this? Otherwise, I could try and rebase your work and finish it off...

[patriksvensson]

@dwijnand Go ahead! I ran out of free time and encountered a lot of merge conflicts, and then the PR was closed because of inactivity 😄

[patriksvensson]

@dwijnand I think that the PR is close to completion, but can't remember to be honest.