"conflicting associated type bounds when expanding trait alias", but there is no actual conflict #146548
Description
I tried this code:
#![feature(trait_alias)] trait Foo { type Assoc; } trait Alias = Foo<Assoc = fn(&())>; type Dyn = dyn Alias<Assoc = fn(&())>;I expected to see this happen: It compiles, just as it would if fn(&()) were replaced with i32
Instead, this happened:
error: conflicting associated type bounds for `Assoc` when expanding trait alias --> src/lib.rs:9:12 | 7 | trait Alias = Foo<Assoc = fn(&())>; | --------------- `Assoc` is specified to be `for<'a> fn(&'a ())` here 8 | 9 | type Dyn = dyn Alias<Assoc = fn(&())>; | ^^^^^^^^^^---------------^ | | | `Assoc` is specified to be `for<'a> fn(&'a ())` here AIUI this is a consequence of #136458?
@rustbot label T-types F-trait_alias A-dyn-trait A-associated-items requires-nightly
Meta
rustc --version --verbose:
rustc 1.91.0-nightly (02c7b1a7a 2025-09-13) binary: rustc commit-hash: 02c7b1a7ac1d739663878030510508372e46f254 commit-date: 2025-09-13 host: x86_64-unknown-linux-gnu release: 1.91.0-nightly LLVM version: 21.1.1