Describe the bug

When using comments within generic type parameters of a trait, rustfmt corrupts the code as follows:

Input

pub trait Something< A, // some comment B, C > { fn a(&self, x: A) -> i32; fn b(&self, x: B) -> i32; fn c(&self, x: C) -> i32; }

Output

pub trait Something< A, // some comment B, C, > // some comment B, C > { fn a(&self, x: A) -> i32; fn b(&self, x: B) -> i32; fn c(&self, x: C) -> i32; }

The same applies for /* block comments */:

Input

pub trait Something< A, /* some comment */ B, C > { fn a(&self, x: A) -> i32; fn b(&self, x: B) -> i32; fn c(&self, x: C) -> i32; }

Output

pub trait Something<A, /* some comment */ B, C> /* some comment */ B, C > { fn a(&self, x: A) -> i32; fn b(&self, x: B) -> i32; fn c(&self, x: C) -> i32; } 

However, this issue doesn't seem to appear for fns and structs.

To Reproduce

• Trait with single-line-comment (broken) - Playground
• Trait with block comment (broken) - Playground
• Struct with single-line-comment (not broken, just for comparison) - Playground
• Function with single-line-comment (not broken, just for comparison) - Playground

I ran rustfmt without any parameters, so just rustfmt some-file-containing-the-example-above.rs.

Expected behavior

I would expect the same formatting as for structs and fns (see the struct playground linked above).

Meta

• rustfmt version: rustfmt 1.4.30-nightly (acd94866 2020-12-20)
• From where did you install rustfmt?: rustup (nightly toolchain)
• How do you run rustfmt: rustfmt +nightly

Additional remarks

• I didn't find any existing issues matching this problem description, Const generic parameter following a comment gets corrupted #4263 looks a bit similar, though.
• Thank you all very much for maintaining this project, it's incredibly useful.
• I'm still a noob at writing rust, so I'm sorry if this is not actually a bug, but rather some mistake on my side.