Deleted comments in type aliases

[AndrewKvalheim]

Some inline comments in type alias declarations are removed during formatting.

Steps to reproduce:

$ rustfmt --version
rustfmt 1.4.38-stable (9d1b210 2022-02-23)
$ rustfmt --emit stdout <(echo 'type Cycle = [u64 /* seconds */; 3];')

Expected output:

type Cycle = [u64 /* seconds */; 3];

Actual output:

type Cycle = [u64; 3];

[ytmimi]

Thanks for the report!

It's likely that rustfmt isn't expecting to find a comment there, and isn't looking out for it when reformatting the code.

[ytmimi]

The issue can be tracked down to the Rewrite impl for ast::Ty. Specifically we're looking at the array case:

rustfmt/src/types.rs

Lines 805 to 812 in 7d6ca7c

	ast::TyKind::Array(ref ty, ref repeats) => rewrite_pair(
	&**ty,
	&*repeats.value,
	PairParts::new("[", "; ", "]"),
	context,
	shape,
	SeparatorPlace::Back,
	),

From what I can tell There's no straightforward way to fix this since we lose all Span information once we call rewrite_pair. However if #5296 gets merged we should have a much easier time fixing this by following the approach used to recover comments for ast::ExprKind::Cast.