mirror of https://github.com/rust-lang/rust
30 lines
965 B
Rust
30 lines
965 B
Rust
// Test an `exists<'a> { forall<'b> { 'a = 'b } }` pattern -- which should not compile!
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//
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// In particular, we test this pattern in trait solving, where it is not connected
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// to any part of the source code.
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use std::cell::Cell;
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trait Trait<T> {}
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fn foo<T>()
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where
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T: Trait<for<'b> fn(Cell<&'b u32>)>,
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{
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}
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impl<'a> Trait<fn(Cell<&'a u32>)> for () {}
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fn main() {
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// Here, proving that `(): Trait<for<'b> fn(&'b u32)>` uses the impl:
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//
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// - The impl provides the clause `forall<'a> { (): Trait<fn(&'a u32)> }`
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// - We instantiate `'a` existentially to get `(): Trait<fn(&?a u32)>`
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// - We unify `fn(&?a u32)` with `for<'b> fn(&'b u32)`
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// - This requires (among other things) instantiating `'b` universally,
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// yielding `fn(&!b u32)`, in a fresh universe U1
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// - So we get `?a = !b` but the universe U0 assigned to `?a` cannot name `!b`.
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foo::<()>(); //~ ERROR implementation of `Trait` is not general enough
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}
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