41 lines
1.1 KiB
Rust
41 lines
1.1 KiB
Rust
// Regression test for #46989:
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//
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// In the move to universes, this test started passing.
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// It is not necessarily WRONG to do so, but it was a bit
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// surprising. The reason that it passed is that when we were
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// asked to prove that
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//
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// for<'a> fn(&'a i32): Foo
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//
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// we were able to use the impl below to prove
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//
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// fn(&'empty i32): Foo
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//
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// and then we were able to prove that
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//
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// fn(&'empty i32) = for<'a> fn(&'a i32)
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//
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// This last fact is somewhat surprising, but essentially "falls out"
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// from handling variance correctly. In particular, consider the subtyping
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// relations. First:
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//
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// fn(&'empty i32) <: for<'a> fn(&'a i32)
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//
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// This holds because -- intuitively -- a fn that takes a reference but doesn't use
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// it can be given a reference with any lifetime. Similarly, the opposite direction:
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//
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// for<'a> fn(&'a i32) <: fn(&'empty i32)
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//
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// holds because 'a can be instantiated to 'empty.
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trait Foo {}
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impl<A> Foo for fn(A) {}
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fn assert_foo<T: Foo>() {}
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fn main() {
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assert_foo::<fn(&i32)>();
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//~^ ERROR implementation of `Foo` is not general enough
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}
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