Missing suggestion "remove semicolon" for mismatched types compile error

[PrototypeNM1]

I tried this code:

fn return_tuple() -> (f32) {
    (3.1415);
}

I expected to see this happen:

A error message suggesting to "consider removing this semicolon" with the relevant code highlighted as in prior releases.

Instead, this happened:

error[E0308]: mismatched types
 --> src/lib.rs:1:23
  |
1 | fn return_tuple() -> (i32) {
  |    ------------       ^^^ expected `i32`, found `()`
  |    |
  |    implicitly returns `()` as its body has no tail or `return` expression

Meta

rustc --version --verbose:

1.45.2
1.47.0-nightly (2020-08-19 32c654a9795b0d88541e)

Issue likely relates to issue #67971 and PR #71894.

This is a significant issue as it's a repeat stumbling block for new users of Rust. See https://www.reddit.com/r/rust/comments/i6yqng/hey_rustaceans_got_an_easy_question_ask_here/g28ambz.

[tesuji]

If you want to return a tuple of a f32, try:

fn return_tuple() -> (f32,) {
    (3.1415);
}

[PrototypeNM1]

I oversimplified the example. Here is the motivating example.

[jonas-schievink]

The suggestion would be incorrect for that playground example. For the original example in the issue, the "help: consider removing this semicolon" is emitted.

[PrototypeNM1]

The suggestion would be incorrect for that playground example. For the original example in the issue, the "help: consider removing this semicolon" is emitted.

Ack, thought I had checked that. Sorry for the noise.

[PrototypeNM1]

I do wonder if this still warrants investigation. The error message as is is not helpful for people not already familiar with Rust syntax. With the (incorrect) semicolon removal suggestion a new user can start to unravel the error (remove semicolon, identify they're returning the wrong types). Not suggesting the wrong suggestion is the right fix, but some path to correctly unraveling the error is preferable.

Currently they have to reason through two very nonintuitive things, returning () means nothing is being returned, which means there's an unnecessary semicolon at the end, the normal error that would have popped up is not there because the types are wrong if they did remove the semicolon.