[type error] when wrongly destructing boxes of ints

[matthiaskrgr]

Given the following code:

#![feature(box_syntax)]
#![feature(half_open_range_patterns_in_slices)]
fn main() {
    let [_y..] = [box 1, box 2];
}

The current output is:

error[E0425]: cannot find value `_y` in this scope
 --> 4a310255aac576a3d3d7ede99bff59ef38f2fb87.rs:4:10
  |
4 |     let [_y..] = [box 1, box 2];
  |          ^^ not found in this scope

error[E0527]: pattern requires 1 element but array has 2
 --> 4a310255aac576a3d3d7ede99bff59ef38f2fb87.rs:4:9
  |
4 |     let [_y..] = [box 1, box 2];
  |         ^^^^^^ expected 2 elements

error[E0029]: only `char` and numeric types are allowed in range patterns
 --> 4a310255aac576a3d3d7ede99bff59ef38f2fb87.rs:4:10
  |
4 |     let [_y..] = [box 1, box 2];
  |          ^^ this is of type `[type error]` but it should be `char` or numeric

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0029, E0425, E0527.
For more information about an error, try `rustc --explain E0029`.

We shouldn't show [type error] here.

[lcnr]

without box_syntax

#![feature(half_open_range_patterns_in_slices)]
fn main() {
    let [_y..] = [Box::new(1), Box::new(2)];
}

[matthiaskrgr]

another one

fn digit() -> str {
	return {};
}

error[E0308]: mismatched types
 --> 0e1a330c6631176565a0f9d144ef565d69e68583.rs:2:9
  |
2 |     return {};
  |            ^^ expected `str`, found `()`

error[E0277]: the size for values of type `str` cannot be known at compilation time
 --> 0e1a330c6631176565a0f9d144ef565d69e68583.rs:1:15
  |
1 | fn digit() -> str {
  |               ^^^ doesn't have a size known at compile-time
2 |     return {};
  |            -- this returned value is of type `[type error]`
  |
  = help: the trait `Sized` is not implemented for `str`
  = note: the return type of a function must have a statically known size

[lyming2007]

What ideal output would you suggest? Should we remove the suggestion line like:

error[E0308]: mismatched types
 --> 0e1a330c6631176565a0f9d144ef565d69e68583.rs:2:9
  |
2 |     return {};
  |            ^^ expected `str`, found `()`

error[E0277]: the size for values of type `str` cannot be known at compilation time
 --> 0e1a330c6631176565a0f9d144ef565d69e68583.rs:1:15
  |
1 | fn digit() -> str {
  |               ^^^ doesn't have a size known at compile-time
2 |     return {};
  |
  = help: the trait `Sized` is not implemented for `str`
  = note: the return type of a function must have a statically known size

[compiler-errors]

Ideally we should be checking that the return type is suggestable. If it's not suggestable, don't mention it.

[lyming2007]

@rustbot claim

[estebank]

I actually believe that neither the E0029 nor the E0277 should have been emitted. I would check explicitly for ty.references_error() and change the error to be err.delay_as_bug() (that way the error isn't printed out, but rustc will ICE if no other error is emitted, which should have happened).

[lyming2007]

I actually believe that neither the E0029 nor the E0277 should have been emitted. I would check explicitly for ty.references_error() and change the error to be err.delay_as_bug() (that way the error isn't printed out, but rustc will ICE if no other error is emitted, which should have happened).

The PR #106499 will prevent E0029 and E0277 from printing out after checking the type references.