Custom `rustfmt` commands cannot use relative executable paths

[ecstatic-morse]

While trying to make rust-analyzer use the bootstrap version of rustfmt inside rustc, @jonas-schievink discovered that using a relative path to rustfmt won't work:

Ah, looks like it adjusts the working dir dynamically, so it can't find the command with a relative path

https://github.com/rust-analyzer/rust-analyzer/blob/d51c1f62178c383363a2d95e865131d9a7b969d0/crates/rust-analyzer/src/main_loop/handlers.rs#L651-L655

As a workaround, you can specify an absolute path, but I was thinking we could canonicalize the first "shell word" if it looks like a path (e.g., ./rustfmt or build/rustfmt but not rustfmt2). This would require some sort of library that can do shell word-splitting, however. Perhaps there is a better way?

The which crate would be helpful for part of this.

[RalfJung]

Curiously, relative paths do work for rust-analyzer.checkOnSave.overrideCommand, so it is somewhat surprising that they do not work for other overrides.

[ecstatic-morse]

I assume it's because checkOnSave doesn't change the current_dir depending on the file like rustfmt does. I haven't checked though.

[oxalica]

According to the doc, current_dir may effect the resolution of relative program name. It's better to canonicalize the relative command path first.

But why do we need to set current_dir for rustfmt here?

[matklad]

But why do we need to set current_dir for rustfmt here?

Not sure there's a super-grand design here, but we do want rustfmt to pick up rustfmt.toml. Hm, is tihs right at all though? Like if I run rustfmt foo/bar/barz/qux.toml, will it pick the rustfmt.toml at foo/bar/rustfmt.toml? I think it should, so this current_dir patching could be removed....

Separately, I feel that semantics of relative paths in config should be independent of the cwd of the language server.

[lnicola]

@ecstatic-morse Can you test this again? The chdir was removed at some point and added back in #7371, but only for the default (non-overridden) case.

(Marking S-actionable, if you look at this in the future and the OP hasn't answered, ping me so we can close it.)

[RalfJung]

I now set the rustfmt command to ./build/x86_64-unknown-linux-gnu/stage0/bin/rustfmt and that seems to work here. :)

[mrchantey]

Is it the expected behavior that this vs code setting should not work?

{
"rust-analyzer.rustfmt.extraArgs": [
  "--config-path",
  "./config",
  ]
}

If so, what is the workaround for a file in ./config/rustfmt.toml? At the moment I'm using an absolute path in workspace settings but thats not portable:

{
"rust-analyzer.rustfmt.extraArgs": [
  "--config-path",
  "C:/Users/Example/Project/config",
  ]
}