From 218caa410aa38c29984be31a5229b9fa717560ee Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 17 Apr 2024 14:19:13 +0200 Subject: Merging upstream version 1.68.2+dfsg1. Signed-off-by: Daniel Baumann --- tests/ui/higher-rank-trait-bounds/issue-46989.rs | 40 ++++++++++++++++++++++++ 1 file changed, 40 insertions(+) create mode 100644 tests/ui/higher-rank-trait-bounds/issue-46989.rs (limited to 'tests/ui/higher-rank-trait-bounds/issue-46989.rs') diff --git a/tests/ui/higher-rank-trait-bounds/issue-46989.rs b/tests/ui/higher-rank-trait-bounds/issue-46989.rs new file mode 100644 index 000000000..4a09f4be1 --- /dev/null +++ b/tests/ui/higher-rank-trait-bounds/issue-46989.rs @@ -0,0 +1,40 @@ +// Regression test for #46989: +// +// In the move to universes, this test started passing. +// It is not necessarily WRONG to do so, but it was a bit +// surprising. The reason that it passed is that when we were +// asked to prove that +// +// for<'a> fn(&'a i32): Foo +// +// we were able to use the impl below to prove +// +// fn(&'empty i32): Foo +// +// and then we were able to prove that +// +// fn(&'empty i32) = for<'a> fn(&'a i32) +// +// This last fact is somewhat surprising, but essentially "falls out" +// from handling variance correctly. In particular, consider the subtyping +// relations. First: +// +// fn(&'empty i32) <: for<'a> fn(&'a i32) +// +// This holds because -- intuitively -- a fn that takes a reference but doesn't use +// it can be given a reference with any lifetime. Similarly, the opposite direction: +// +// for<'a> fn(&'a i32) <: fn(&'empty i32) +// +// holds because 'a can be instantiated to 'empty. + +trait Foo {} + +impl Foo for fn(A) {} + +fn assert_foo() {} + +fn main() { + assert_foo::(); + //~^ ERROR implementation of `Foo` is not general enough +} -- cgit v1.2.3