Jonas Schievink c7a67209c8 Rollup merge of #79287 - jonas-schievink:const-trait-impl, r=oli-obk ... Allow using generic trait methods in `const fn` Next step for https://github.com/rust-lang/rust/issues/67792, this now also allows code like the following: ```rust struct S; impl const PartialEq for S { fn eq(&self, _: &S) -> bool { true } } const fn equals_self<T: PartialEq>(t: &T) -> bool { *t == *t } pub const EQ: bool = equals_self(&S); ``` This works by threading const-ness of trait predicates through trait selection, in particular through `ParamCandidate`, and exposing it in the resulting `ImplSource`. Since this change makes two bounds `T: Trait` and `T: ?const Trait` that only differ in their const-ness be treated like different bounds, candidate winnowing has been changed to drop the `?const` candidate in favor of the const candidate, to avoid ambiguities when both a const and a non-const bound is present.		2020-11-23 15:25:44 +01:00
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src	Rollup merge of #79287 - jonas-schievink:const-trait-impl, r=oli-obk	2020-11-23 15:25:44 +01:00
Cargo.toml	Added some unit tests as requested	2020-11-11 16:40:17 -08:00