cargo reports incorrect compiler-artifact path for rustdoc json

[Nemo157]

Problem

When running a cargo rustdoc --message-format=json -- --output-format=json -Zunstable-options command the path reported for the final compiler-artifact message is wrong.

Steps

> cargo rustdoc --message-format=json -- --output-format=json -Zunstable-options | jq -sr 'last(.[] | select(.reason == "compiler-artifact")) | .executable'
 Documenting cargo-doc-tree v0.1.0 (/home/nemo157/sources/cargo-doc-tree)
    Finished dev [unoptimized + debuginfo] target(s) in 0.90s
/home/nemo157/.cargo/shared-target/doc/cargo_doc_tree/index.html
> ls /home/nemo157/.cargo/shared-target/doc/cargo_doc_tree/index.html /home/nemo157/.cargo/shared-target/doc/cargo_doc_tree.json
ls: cannot access '/home/nemo157/.cargo/shared-target/doc/cargo_doc_tree/index.html': No such file or directory
/home/nemo157/.cargo/shared-target/doc/cargo_doc_tree.json

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.58.0-nightly (ad50d0d26 2021-11-17)
release: 1.58.0
commit-hash: ad50d0d266213e0cc4f6e526a39d96faae9a3842
commit-date: 2021-11-17
host: x86_64-unknown-linux-gnu
libgit2: 1.3.0 (sys:0.13.23 vendored)
libcurl: 7.79.1-DEV (sys:0.4.50+curl-7.79.1 vendored ssl:OpenSSL/1.1.1l)
os: Arch Linux [64-bit]

[Nemo157]

Hmmm, also relevant, that was in a binary crate, in a library-only crate there is no path given in the final message.

[ehuss]

Including the path in the "executable" field was a mistake. I have posted #10171 to fix that.

As for getting the path when using the JSON output, that is a bit tricky. Cargo doesn't use the flags passed to cargo rustdoc or cargo rustc when computing the potential outputs. Cargo probably won't ever parse those arguments, and rustdoc doesn't have a mechanism to report its outputs.

Perhaps eventually a flag for the output format could be wired directly into cargo rustdoc if the JSON output is ever stabilized.

[jyn514]

Cargo probably won't ever parse those arguments, and rustdoc doesn't have a mechanism to report its outputs.

Perhaps eventually a flag for the output format could be wired directly into cargo rustdoc if the JSON output is ever stabilized.

I think it would be simpler to add a way for rustdoc to report its outputs; it shouldn't be too hard to do. What format does rustc use for that, something with --emit presumably?

[ehuss]

Primarily through --print=file-names. It runs the command rustc - --crate-name ___ --print=file-names --crate-type bin --crate-type rlib --crate-type dylib --crate-type cdylib --crate-type staticlib --crate-type proc-macro, so that it knows the prefix and suffix of every crate type. Then there is a large amount of code for figuring out for different targets and scenarios the kind of outputs different commands generate.

Compared to rustdoc which is really basic:

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

Lines 399 to 409 in 263b169

	CompileMode::Doc { .. } => {
	let path = self
	.out_dir(unit)
	.join(unit.target.crate_name())
	.join("index.html");
	vec![OutputFile {
	path,
	hardlink: None,
	export_path: None,
	flavor: FileFlavor::Normal,
	}]

Cargo needs to know the outputs before it runs rustc. rustdoc is a bit different, and I'm not sure how it could work to report the outputs.