Rustfmt: stdin formatting fails if mod file not found

[johannhof]

echo "mod abc; fn main(){let a =1\n; \n let b = 2;}" | rustfmt

result:

stdin:1:5: 1:8 error: file not found for module `abc`
stdin:1 mod abc; fn main(){let a =1
            ^~~

For file formatting it's quite okay since you have a location to search modules in, but obviously this behavior is not ideal when piping from stdin.

The error is generated by syntex_syntax. Maybe we can parse syntax items more granularly and ignore this kind of error.

[matthew-piziak]

Yeah, this is a problem when fmting files over Emacs TRAMP, for example.

[vadixidav]

Is there a temporary solution to this? For instance, in VS Code can we pass an argument to RLS that will tell it to look in the source directory for the modules?

[vadixidav]

Also, in VS Code, it automatically switches to the output panel from the problems panel whenever it outputs this error. So every time I save the file, I have to switch panels. Is there a workaround to this as well?

[nrc]

Hmm, I'm not really sure how to fix this. Even if we get the info from VSCode or emacs or whatever, the hard part is how to communicate that to the parser (and actually if we are getting in to changing the parser, then just stopping at mod statements is probably the easiest and best thing to do). I think the best fix here is just to add a flag to the parser to not parse out of line modules. That doesn't feel like it should be too hard to do. If anyone wants a good first rustc bug, I'd be happy to mentor.

[nrc]

I have a PR to libsyntax that should fix this, at least on the libsyntax branch - https://github.com/rust-lang/rust/pull/42071

[nrc]

This is fixed on the libsyntax branch now