diff options
Diffstat (limited to 'compiler/rustc_trait_selection/src/traits/specialize/mod.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/specialize/mod.rs | 22 |
1 files changed, 17 insertions, 5 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs index 91a0599a3be..1430cfae51f 100644 --- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs @@ -225,11 +225,17 @@ pub(super) fn specialization_enabled_in(tcx: TyCtxt<'_>, _: LocalCrate) -> bool tcx.features().specialization() || tcx.features().min_specialization() } -/// Is `impl1` a specialization of `impl2`? +/// Is `specializing_impl_def_id` a specialization of `parent_impl_def_id`? /// -/// Specialization is determined by the sets of types to which the impls apply; -/// `impl1` specializes `impl2` if it applies to a subset of the types `impl2` applies -/// to. +/// For every type that could apply to `specializing_impl_def_id`, we prove that +/// the `parent_impl_def_id` also applies (i.e. it has a valid impl header and +/// its where-clauses hold). +/// +/// For the purposes of const traits, we also check that the specializing +/// impl is not more restrictive than the parent impl. That is, if the +/// `parent_impl_def_id` is a const impl (conditionally based off of some `~const` +/// bounds), then `specializing_impl_def_id` must also be const for the same +/// set of types. #[instrument(skip(tcx), level = "debug")] pub(super) fn specializes( tcx: TyCtxt<'_>, @@ -339,8 +345,14 @@ pub(super) fn specializes( return false; } - // If the parent impl is const, then the specializing impl must be const. + // If the parent impl is const, then the specializing impl must be const, + // and it must not be *more restrictive* than the parent impl (that is, + // it cannot be const in fewer cases than the parent impl). if tcx.is_conditionally_const(parent_impl_def_id) { + if !tcx.is_conditionally_const(specializing_impl_def_id) { + return false; + } + let const_conditions = ocx.normalize( cause, param_env, |