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#[derive(Eq)] struct Foo { x: u32 } impl PartialEq for Foo { fn eq(&self, _: &Foo) -> bool { false // ha ha! } } const FOO: Foo = Foo { x: 0 }; fn main() { let y = Foo { x: 1 }; match y { FOO => { } //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]` _ => { } } }