diff options
3 files changed, 39 insertions, 1 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs index fa94aa19abd..da17a9c3da6 100644 --- a/compiler/rustc_trait_selection/src/traits/coherence.rs +++ b/compiler/rustc_trait_selection/src/traits/coherence.rs @@ -746,8 +746,17 @@ impl<'tcx> TypeVisitor<'tcx> for OrphanChecker<'tcx> { result } - // FIXME: Constants should participate in orphan checking. fn visit_const(&mut self, _c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> { + // All possible values for a constant parameter already exist + // in the crate defining the trait, so they are always non-local. + // + // Because there's no way to have an impl where the first local + // generic argument is a constant, we also don't have to fail + // the orphan check when encountering a parameter or a generic constant. + // + // This means that we can completely ignore constants during the orphan check. + // + // See `src/test/ui/coherence/const-generics-orphan-check-ok.rs` for examples. ControlFlow::CONTINUE } } diff --git a/src/test/ui/coherence/auxiliary/trait-with-const-param.rs b/src/test/ui/coherence/auxiliary/trait-with-const-param.rs new file mode 100644 index 00000000000..a44eb14f8e4 --- /dev/null +++ b/src/test/ui/coherence/auxiliary/trait-with-const-param.rs @@ -0,0 +1 @@ +pub trait Trait<const N: usize, T> {} diff --git a/src/test/ui/coherence/const-generics-orphan-check-ok.rs b/src/test/ui/coherence/const-generics-orphan-check-ok.rs new file mode 100644 index 00000000000..217e8aed234 --- /dev/null +++ b/src/test/ui/coherence/const-generics-orphan-check-ok.rs @@ -0,0 +1,28 @@ +// check-pass +// aux-build:trait-with-const-param.rs +extern crate trait_with_const_param; +use trait_with_const_param::*; + +// Trivial case, const param after local type. +struct Local1; +impl<const N: usize, T> Trait<N, T> for Local1 {} + +// Concrete consts behave the same as foreign types, +// so this also trivially works. +impl Trait<3, Local1> for i32 {} + +// This case isn't as trivial as we would forbid type +// parameters here, we do allow const parameters though. +// +// The reason that type parameters are forbidden for +// `impl<T> Trait<T, LocalInA> for i32 {}` is that another +// downstream crate can add `impl<T> Trait<LocalInB, T> for i32`. +// As these two impls would overlap we forbid any impls which +// have a type parameter in front of a local type. +// +// With const parameters this issue does not exist as there are no +// constants local to another downstream crate. +struct Local2; +impl<const N: usize> Trait<N, Local2> for i32 {} + +fn main() {} |