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Separate consider_unsize_to_dyn_candidate from other unsize candidates

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This commit is contained in:
Michael Goulet 2023-08-14 23:37:06 +00:00
parent 1b198b3a19
commit 7d8563c602
4 changed files with 94 additions and 54 deletions
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43
compiler/rustc_trait_selection/src/solve/assembly/mod.rs
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@ -281,23 +281,27 @@ pub(super) trait GoalKind<'tcx>:
) -> QueryResult<'tcx>;
/// Consider (possibly several) candidates to upcast or unsize a type to another
/// type.
///
/// The most common forms of unsizing are array to slice, and concrete (Sized)
/// type into a `dyn Trait`. ADTs and Tuples can also have their final field
/// unsized if it's generic.
///
/// `dyn Trait1` can be unsized to `dyn Trait2` if they are the same trait, or
/// if `Trait2` is a (transitive) supertrait of `Trait2`.
/// type, excluding the coercion of a sized type into a `dyn Trait`.
///
/// We return the `BuiltinImplSource` for each candidate as it is needed
/// for unsize coercion in hir typeck and because it is difficult to
/// otherwise recompute this for codegen. This is a bit of a mess but the
/// easiest way to maintain the existing behavior for now.
fn consider_builtin_unsize_candidates(
fn consider_structural_builtin_unsize_candidates(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
) -> Vec<(CanonicalResponse<'tcx>, BuiltinImplSource)>;
/// Consider the `Unsize` candidate corresponding to coercing a sized type
/// into a `dyn Trait`.
///
/// This is computed separately from the rest of the `Unsize` candidates
/// since it is only done once per self type, and not once per
/// *normalization step* (in `assemble_candidates_via_self_ty`).
fn consider_unsize_to_dyn_candidate(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
) -> QueryResult<'tcx>;
}
impl<'tcx> EvalCtxt<'_, 'tcx> {
@ -312,6 +316,8 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
let mut candidates = self.assemble_candidates_via_self_ty(goal, 0);
self.assemble_unsize_to_dyn_candidate(goal, &mut candidates);
self.assemble_blanket_impl_candidates(goal, &mut candidates);
self.assemble_param_env_candidates(goal, &mut candidates);
@ -530,6 +536,23 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
}
}
fn assemble_unsize_to_dyn_candidate<G: GoalKind<'tcx>>(
&mut self,
goal: Goal<'tcx, G>,
candidates: &mut Vec<Candidate<'tcx>>,
) {
let tcx = self.tcx();
if tcx.lang_items().unsize_trait() == Some(goal.predicate.trait_def_id(tcx)) {
match G::consider_unsize_to_dyn_candidate(self, goal) {
Ok(result) => candidates.push(Candidate {
source: CandidateSource::BuiltinImpl(BuiltinImplSource::Misc),
result,
}),
Err(NoSolution) => (),
}
}
}
fn assemble_blanket_impl_candidates<G: GoalKind<'tcx>>(
&mut self,
goal: Goal<'tcx, G>,
@ -610,7 +633,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
// There may be multiple unsize candidates for a trait with several supertraits:
// `trait Foo: Bar<A> + Bar<B>` and `dyn Foo: Unsize<dyn Bar<_>>`
if lang_items.unsize_trait() == Some(trait_def_id) {
for (result, source) in G::consider_builtin_unsize_candidates(self, goal) {
for (result, source) in G::consider_structural_builtin_unsize_candidates(self, goal) {
candidates.push(Candidate { source: CandidateSource::BuiltinImpl(source), result });
}
}