Reject casts to unsized types #17598
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cc @nick29581 |
| fn main() { | ||
| let _foo = &[1u, 2] as [uint]; | ||
| //~^ ERROR cast to unsized type: `&[uint, .. 2]` as `[uint]` | ||
| //~^^ NOTE did you mean `&[uint]`? |
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Note that this cast doesn't work at the moment, so the note is a bit wrong. Should probably suggest using an implicit coercion.
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But please add a check for &obj types.
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I'll suggest using an implicit coercion if the cast type is not a trait
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Force-pushed some changes. It will now suggest using an implicit coerceion where the explicit cast doesn't presently work, and will only suggest boxing an expression when attempting to cast to a trait, since this is generally the only time boxing is appropriate. |
This prevents ICEs or less helpful diagnostics if typeck proceeds further. Closes issue rust-lang#17441
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Changed the note suggesting |
| if !ty::type_is_sized(fcx.tcx(), t_1) { | ||
| let tstr = fcx.infcx().ty_to_string(t_1); | ||
| fcx.type_error_message(span, |actual| { | ||
| format!("cast to unsized type: `{}` as `{}`", actual, tstr) |
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I think the error message should only show the unsized type, not the actual type too. Otherwise its a bit confusing
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I patterned it after messages in the existing code, e.g. "cast to nil: {}as{}". I can still change it.
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r=me with that error message change. |
feat: add preliminary support for `+ use<..>` `precise_capturing` syntax
## Summary
This PR adds basic support for the following syntax.
```rs
fn captures<'a: 'a, 'b: 'b, T>() -> impl Sized + use<'b, T> {}
// ~~~~~~~~~~~~~~~~~~~~~~~
// This opaque type does not capture `'a`.
fn outlives<'o, T: 'o>(_: T) {}
fn caller<'o, 'a, 'b: 'o, T: 'o>() {
// ~~
// ^ Note that we don't need `'a: 'o`.
outlives::<'o>(captures::<'a, 'b, T>());
}
```
Related to rust-lang#17598
feat: add preliminary support for `+ use<..>` `precise_capturing` syntax
## Summary
This PR adds basic support for the following syntax.
```rs
fn captures<'a: 'a, 'b: 'b, T>() -> impl Sized + use<'b, T> {}
// ~~~~~~~~~~~~~~~~~~~~~~~
// This opaque type does not capture `'a`.
fn outlives<'o, T: 'o>(_: T) {}
fn caller<'o, 'a, 'b: 'o, T: 'o>() {
// ~~
// ^ Note that we don't need `'a: 'o`.
outlives::<'o>(captures::<'a, 'b, T>());
}
```
Related to rust-lang#17598
feat: add preliminary support for `+ use<..>` `precise_capturing` syntax
## Summary
This PR adds basic support for the following syntax.
```rs
fn captures<'a: 'a, 'b: 'b, T>() -> impl Sized + use<'b, T> {}
// ~~~~~~~~~~~~~~~~~~~~~~~
// This opaque type does not capture `'a`.
fn outlives<'o, T: 'o>(_: T) {}
fn caller<'o, 'a, 'b: 'o, T: 'o>() {
// ~~
// ^ Note that we don't need `'a: 'o`.
outlives::<'o>(captures::<'a, 'b, T>());
}
```
Related to rust-lang#17598
This closes issue #17441 and generally gives more helpful diagnostics.