cargo rustc --workspace/--exclude

[xd009642]

So I'm working on tarpaulin, and I'm trying to solve an issue where linker flags of dependencies can conflict with the linker flags I need to set for code coverage, namely -C link-dead-code (conflict issue rust-lang/rust#64685). It should also keep the target directory smaller by not having dead code for all the dependencies included and prevent rebuilds when working with tarpaulin making things faster. So that's the motivation.

Now my idea to solve this is using cargo rustc to just pass the flags to the crate only. However if the user is using workspaces and has multiple packages in their project all the packages need link-dead-code applied not just the one under test. But I get the feeling from the docs that this isn't how cargo rustc works?

Providing cargo rustc works as I've grokked it, I was thinking that making the flags compatible with cargo build/test/etc and allowing it to operate on a whole workspace would be a solution.

Also, I'll need this to work with cargo test --bins/--examples/--doc/--lib/--benches/--tests with the compiled artefacts and anything in the project workspace linked with dead code. But that's just a side note in case I'm wrong and there's a better solution for doing this either with cargo rustc or a different cargo command

[ehuss]

You are correct, cargo rustc only applies to the final artifact.

I would suggest looking at RUSTC_WORKSPACE_WRAPPER (see #8143), which is used for all workspace members. You could inject your own flags via that.

[xd009642]

Oh cool, so that's available on stable as well? Or does the tracking issue mean it's not yet on stable rust?

[ehuss]

It is not stable, it requires -Zunstable-options.

[xd009642]

So I'm part way through implementing this and I've got this as compiler output:

 -C link-dead-code --cfg=tarpaulin -C debuginfo=2  rustc --crate-name faktory ...

Is there a way to get the args to appear after rustc? I've had a perusal of the issue and associated PR and didn't spot anything.

In the meantime I'm going to keep looking and adjust it so it should create this monstrosity (which shouldn't work): this didn't work

rustc -C link-dead-code --cfg=tarpaulin -C debuginfo=2  --cfg=tarpaulin_rustc --crate-name faktory ...

I also tried RUSTC="rustc <ARGS>..." which didn't work. Also, considered getting a rustc build-plans and modding it, but they're being removed because of issues so that's a no. And of course looking for a postfix wrapper but I couldn't find mention of one

[ehuss]

RUSTC_WORKSPACE_WRAPPER should point to an executable that replaces rustc. It is passed the path to rustc and all its arguments, and you can just append to the argument list, and execute rustc (the first argument). Here is where cargo clippy uses clippy-driver as a wrapper.

Thinking about it some more, I can see that might be awkward for your use case since you can't pass in arguments via the environment variable, so you would need a dedicated executable for that. I added a note to the tracking issue about that.

[ehuss]

I'm going to close, as I think this seems to be mostly addressed by RUSTC_WORKSPACE_WRAPPER. Feel free to reopen if that is not the case, or if there is some feedback for that feature, please leave a comment on that tracking issue.