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Rollup merge of #133367 - compiler-errors:array-len-mismatch, r=BoxyUwU

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Simplify array length mismatch error reporting (to not try to turn consts into target usizes)

This changes `TypeError::FixedArrayLen` to use `ExpectedFound<ty::Const<'tcx>>` (instead of `ExpectedFound<u64>`), and renames it to `TypeError::ArrayLen`. This allows us to avoid a `try_to_target_usize` call in the type relation, which ICEs when we have a scalar of the wrong bit length (i.e. u8).

This also makes `structurally_relate_tys` to always use this type error kind any time we have a const mismatch resulting from relating the array-len part of `[T; N]`.

This has the effect of changing the error message we issue for array length mismatches involving non-valtree consts. I actually quite like the change, though, since before:

```
LL | fn test<const N: usize, const M: usize>() -> [u8; M] {
   |                                              ------- expected `[u8; M]` because of return type
LL |     [0; N]
   |     ^^^^^^ expected `M`, found `N`
   |
   = note: expected array `[u8; M]`
              found array `[u8; N]`
```

and after, which I think is far less verbose:

```
LL | fn test<const N: usize, const M: usize>() -> [u8; M] {
   |                                              ------- expected `[u8; M]` because of return type
LL |     [0; N]
   |     ^^^^^^ expected an array with a size of M, found one with a size of N
```

The only questions I have are:
1. Should we do something about backticks here? Right now we don't backtick either fully evaluated consts like `2`, or rigid consts like `Foo::BAR`.... but maybe we should? It seems kinda verbose to do for numbers -- maybe we could intercept those specifically.
2. I guess we may still run the risk of leaking unevaluated consts into error reporting like `2 + 1`...?

r? ``@BoxyUwU``

Fixes #126359
Fixes #131101
This commit is contained in:
Michael Goulet 2024-11-26 12:03:44 -05:00 • committed by GitHub
commit cf09718876
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18 changed files with 60 additions and 71 deletions
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13
compiler/rustc_trait_selection/src/error_reporting/infer/mod.rs
View file

@ -1792,12 +1792,12 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
fn suggest_specify_actual_length(
&self,
terr: TypeError<'_>,
trace: &TypeTrace<'_>,
terr: TypeError<'tcx>,
trace: &TypeTrace<'tcx>,
span: Span,
) -> Option<TypeErrorAdditionalDiags> {
let hir = self.tcx.hir();
let TypeError::FixedArraySize(sz) = terr else {
let TypeError::ArraySize(sz) = terr else {
return None;
};
let tykind = match self.tcx.hir_node_by_def_id(trace.cause.body_id) {
@ -1838,9 +1838,14 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
if let Some(tykind) = tykind
&& let hir::TyKind::Array(_, length) = tykind
&& let hir::ArrayLen::Body(ct) = length
&& let Some((scalar, ty)) = sz.found.try_to_scalar()
&& ty == self.tcx.types.usize
{
let span = ct.span();
Some(TypeErrorAdditionalDiags::ConsiderSpecifyingLength { span, length: sz.found })
Some(TypeErrorAdditionalDiags::ConsiderSpecifyingLength {
span,
length: scalar.to_target_usize(&self.tcx).unwrap(),
})
} else {
None
}