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Suggest a trailing comma if a 1-tuple is expected and a parenthesized expression is found This pull request fixes #86100. The following code: ```rust fn main() { let t: (i32,) = (1); } ``` currently produces: ``` warning: unnecessary parentheses around assigned value --> test.rs:2:21 | 2 | let t: (i32,) = (1); | ^^^ help: remove these parentheses | = note: `#[warn(unused_parens)]` on by default error[E0308]: mismatched types --> test.rs:2:21 | 2 | let t: (i32,) = (1); | ------ ^^^ expected tuple, found integer | | | expected due to this | = note: expected tuple `(i32,)` found type `{integer}` error: aborting due to previous error; 1 warning emitted ``` With my changes, I get the same warning and the following error: ``` error[E0308]: mismatched types --> test.rs:2:21 | 2 | let t: (i32,) = (1); | ------ ^^^ expected tuple, found integer | | | expected due to this | = note: expected tuple `(i32,)` found type `{integer}` help: use a trailing comma to create a tuple with one element | 2 | let t: (i32,) = (1,); | ^^^^ ``` i.e. I have added a suggestion to add a trailing comma to create a 1-tuple. This suggestion is only issued if a 1-tuple is expected and the expression (`(1)` in the example above) is surrounded by parentheses and does not already have a tuple type. In this situation, I'd say that it is pretty likely that the user meant to create a tuple.