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Fix const specialization

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This commit is contained in:
Michael Goulet 2024-11-23 01:00:11 +00:00
parent e91fc1bc0c
commit 9bda88bb58
11 changed files with 133 additions and 50 deletions
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22
compiler/rustc_trait_selection/src/traits/specialize/mod.rs
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@ -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,