mirror of https://github.com/rust-lang/rust.git
27 lines
1.1 KiB
Rust
27 lines
1.1 KiB
Rust
//@ revisions: current next
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//@ ignore-compare-mode-next-solver (explicit revisions)
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//@[next] compile-flags: -Znext-solver
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//@ check-pass
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// This caused a regression in a crater run in #132325.
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//
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// The underlying issue is a really subtle implementation detail.
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//
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// When building the `param_env` for `Trait` we start out with its
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// explicit predicates `Self: Trait` and `Self: for<'a> Super<'a, { 1 + 1 }>`.
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//
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// When normalizing the environment we also elaborate. This implicitly
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// deduplicates its returned predicates. We currently first eagerly
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// normalize constants in the unnormalized param env to avoid issues
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// caused by our lack of deferred alias equality.
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//
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// So we actually elaborate `Self: Trait` and `Self: for<'a> Super<'a, 2>`,
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// resulting in a third `Self: for<'a> Super<'a, { 1 + 1 }>` predicate which
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// then gets normalized to `Self: for<'a> Super<'a, 2>` at which point we
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// do not deduplicate however. By failing to handle equal where-bounds in
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// candidate selection, this caused ambiguity when checking that `Trait` is
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// well-formed.
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trait Super<'a, const N: usize> {}
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trait Trait: for<'a> Super<'a, { 1 + 1 }> {}
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fn main() {}
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