From a4b7ed7a42c716ab9f05e351f003d589124fd55d Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 17 Apr 2024 14:18:58 +0200 Subject: Adding upstream version 1.68.2+dfsg1. Signed-off-by: Daniel Baumann --- .../multiple-lifetimes/inverse-bounds.rs | 50 ++++++++++++++++++++++ 1 file changed, 50 insertions(+) create mode 100644 tests/ui/impl-trait/multiple-lifetimes/inverse-bounds.rs (limited to 'tests/ui/impl-trait/multiple-lifetimes/inverse-bounds.rs') diff --git a/tests/ui/impl-trait/multiple-lifetimes/inverse-bounds.rs b/tests/ui/impl-trait/multiple-lifetimes/inverse-bounds.rs new file mode 100644 index 000000000..5251eeee8 --- /dev/null +++ b/tests/ui/impl-trait/multiple-lifetimes/inverse-bounds.rs @@ -0,0 +1,50 @@ +// edition:2018 +// check-pass + +trait Trait<'a, 'b> {} +impl Trait<'_, '_> for T {} + +// `Invert<'a> <: Invert<'b>` if `'b: 'a`, unlike most types. +// +// I am purposefully avoiding the terms co- and contra-variant because +// their application to regions depends on how you interpreted Rust +// regions. -nikomatsakis +struct Invert<'a>(fn(&'a u8)); + +fn upper_bounds<'a, 'b, 'c, 'd, 'e>(a: Invert<'a>, b: Invert<'b>) -> impl Trait<'d, 'e> +where + 'c: 'a, + 'c: 'b, + 'd: 'c, +{ + // Representing the where clauses as a graph, where `A: B` is an + // edge `B -> A`: + // + // ``` + // 'a -> 'c -> 'd + // ^ + // | + // 'b + // ``` + // + // Meanwhile we return a value &'0 u8 where we have the constraints: + // + // ``` + // '0: 'a + // '0: 'b + // '0 in ['d, 'e] + // ``` + // + // Here, ignoring the "in" constraint, the minimal choice for `'0` + // is `'c`, but that is not in the "in set". Still, that reduces + // the range of options in the "in set" to just `'d` (`'e: 'c` + // does not hold). + let p = if condition() { a } else { b }; + p +} + +fn condition() -> bool { + true +} + +fn main() {} -- cgit v1.2.3