rustfmt eats comments in fn return type wrapped in parenthesis

[Centri3]

This code:

fn f() -> (/* is something */ bool) {}

Turns into this:

fn f() -> (bool) {}

Not too big of a deal as this isn't a tuple (due to the missing ,) and doesn't happen with tuples, but it should probably look for a comment here so it's retained after the programmer adds the , (and presumably other types, too)

Doesn't seem to happen in other places (like the type annotation for a local).

[Centri3]

Hm, also happens with fn a() -> /* a */ bool {} but not if it's after the type

[ytmimi]

Thanks for the report.

To give a brief explanation; comments aren't explicitly represented in the AST rustfmt uses when formatting code so rustfmt needs to peek back into the original source code to find and recover comments. It seems that we're not recovering comments when rewriting ast::TyKind::Paren types.

https://github.com/rust-lang/rustfmt/blob/a72613be50f8afa39c2d46f732252463dc9cc14f/src/types.rs#L778-L810

[Centri3]

Seems we're not checking for them right after the arrow as well, in the case of fn a() -> /* a */ bool {}

[ytmimi]

Seems we're not checking for them right after the arrow as well, in the case of fn a() -> / a / bool {}

Yup, that seems to be the case too. Though that's happening on a different code path and I think it might be better to open up a separate issue for that case.

[ytmimi]

@Centri3 Also want to highlight that comments after the type are also removed. e.g. fn f() -> (bool /* comment */) {} becomes fn f() -> (bool) {}

[Centri3]

I'll open a separate issue for the other case.