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Point at array length instead of whole array type - #165516

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Point at array length instead of whole array type#165516
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estebank:point-at-arr-len

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@estebank

@estebank estebank commented Nov 5, 2026 •
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error: the constant `N` is not of type `usize`
  --> $DIR/bad-subst-const-kind.rs:8:31
   |
LL | impl<const N: u64> Q for [u8; N] {
   |                               ^ array length expected `usize`, found `u64`
   |
   = note: the length of array `[u8; N]` must be type `usize`

When evaluating an array type's length we don't have accurate spans for that hir node, because evaluation happens on types. Keep the Span for the whole array type that we can use later to try and find the hir node and extract the right span to use in the diagnostic.

@estebank
Point at array length instead of whole array type
6812404 
```
error: the constant `N` is not of type `usize`
  --> $DIR/bad-subst-const-kind.rs:8:31
   |
LL | impl<const N: u64> Q for [u8; N] {
   |      ------------             ^ array length expected `usize`, found `u64`
   |      |
   |      `N` defined here
   |
   = note: the length of array `[u8; N]` must be type `usize`
```

When evaluating an array type's length we don't have accurate spans for that hir node, because evaluation happens on types. Keep the Span for the whole array type that we can use later to try and find the hir node and extract the right span to use in the diagnostic.
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rustbot commented Nov 5, 2026

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changes to the core type system

cc @lcnr

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Nov 5, 2026
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rustbot commented Nov 5, 2026

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r? @nnethercote

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@estebank

estebank commented Nov 5, 2026

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Will have merge conflicts with #164775.

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rust-bors Bot commented Nov 7, 2026

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☔ The latest upstream changes (presumably #165579) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

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