76 lines
2.0 KiB
Rust
76 lines
2.0 KiB
Rust
// compile-flags: -Ztrait-solver=next
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// known-bug: trait-system-refactor-initiative#60
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// Generalizing a projection containing an inference variable
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// which cannot be named by the `root_vid` can result in ambiguity.
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//
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// Because we do not decrement the universe index when exiting a forall,
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// this can cause unexpected failures.
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//
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// See generalize-proj-new-universe-index-1.rs for more details.
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// For this reproduction we need:
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// - an inference variable with a lower universe
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// - enter a binder to increment the current universe
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// - create a new inference variable which is constrained by proving a goal
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// - equate a projection containing the new variable with the first variable
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// - generalization creates yet another inference variable which is then
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// part of an alias-relate, resulting this to fail with ambiguity.
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//
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// Because we need to enter the binder in-between the creation of the first
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// and second inference variable, this is easiest via
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// `assemble_candidates_after_normalizing_self_ty` because eagerly call
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// `try_evaluate_added_goals` there before creating the inference variables
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// for the impl parameters.
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trait Id {
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type Assoc: ?Sized;
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}
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impl<T: ?Sized> Id for T {
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type Assoc = T;
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}
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// By adding an higher ranked bound to the impl we currently
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// propagate this bound to the caller, forcing us to create a new
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// universe.
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trait IdHigherRankedBound {
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type Assoc: ?Sized;
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}
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impl<T: ?Sized> IdHigherRankedBound for T
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where
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for<'a> T: 'a,
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{
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type Assoc = T;
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}
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trait WithAssoc<T: ?Sized> {
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type Assoc: ?Sized;
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}
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struct Leaf;
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struct Wrapper<U: ?Sized>(U);
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struct Rigid;
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impl<U: ?Sized> WithAssoc<U> for Leaf {
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type Assoc = U;
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}
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impl<Ur: ?Sized> WithAssoc<Wrapper<Ur>> for Rigid
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where
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Leaf: WithAssoc<Ur>,
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{
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type Assoc = <<Leaf as WithAssoc<Ur>>::Assoc as Id>::Assoc;
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}
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fn bound<T: ?Sized, U: ?Sized, V: ?Sized>()
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where
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T: WithAssoc<U, Assoc = V>,
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{
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}
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fn main() {
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bound::<<Rigid as IdHigherRankedBound>::Assoc, <Wrapper<Leaf> as Id>::Assoc, _>()
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}
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