[BUG] - v0.43.0+ cargo-bazel generates bad selects

[timbess]

#2636

After this PR, it seems that tar is now building xattr on windows despite it only being listed as a unix dependency. When I patch the cargo-bazel toolchain to use 0.42.1 binaries with 0.44.0 it generates the proper platform specific selects:

Cargo-Bazel.lock.json v0.44.0 -> v0.42.1

         "deps": {
           "common": [
             {
               "id": "filetime 0.2.20",
               "target": "filetime"
-            },
-            {
-              "id": "xattr 0.2.3",
-              "target": "xattr"
             }
           ],
           "selects": {
             "cfg(unix)": [
               {
                 "id": "libc 0.2.151",
                 "target": "libc"
+              },
+              {
+                "id": "xattr 0.2.3",
+                "target": "xattr"
               }
             ]
           }
         },

[timbess]

I debugged the issue a bit. It seems like the cargo tree query is including all build dependencies which are actually for the host triple, but are being counted towards the target triple here:

rules_rust/crate_universe/src/metadata.rs

Lines 530 to 558 in e3f6258

	let output = self
	.cargo_bin
	.command()?
	.current_dir(manifest_dir)
	.arg("tree")
	.arg("--locked")
	.arg("--manifest-path")
	.arg(manifest_path)
	.arg("--edges")
	.arg("normal,build,dev")
	.arg("--prefix=depth")
	// https://doc.rust-lang.org/cargo/commands/cargo-tree.html#tree-formatting-options
	.arg("--format=|{p}|{f}|")
	.arg("--color=never")
	.arg("--workspace")
	.arg("--target")
	.arg(target_triple.to_cargo())
	.env("RUSTC", &self.rustc_bin)
	.stdout(std::process::Stdio::piped())
	.stderr(std::process::Stdio::piped())
	.spawn()
	.with_context(|| {
	format!(
	"Error spawning cargo in child process to compute features for target '{}', manifest path '{}'",
	target_triple,
	manifest_path.display()
	)
	})?;
	target_triple_to_child.insert(target_triple, output);

If I remove build from the edges, it fixes it:

     .arg("--edges") 
     .arg("normal,dev") 

I added a second query for just build deps, but it seems cargo tree doesn't include transitive normal deps under build deps unfortunately.

I couldn't really find a way to include whether it's a build dependency in the cargo tree format string which would be a more ideal solution IMO.

[timbess]

I made a PR against Cargo to hopefully add enough metadata to fix this issue rust-lang/cargo#14008

Nevermind just found this #2212, I was going down the wrong path with that solution.