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Track rewrites in IdentifiedFacetType (#7866)

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This allows us to collect rewrites from named constraints and use them
to initialize the witness table for an `impl as` statement.

Only rewrites from extend constraints are tracked, as other constraints
should turn into equality constraints, as they don't modify the witness
table.
This commit is contained in:
Dana Jansens
2026-09-30 18:07:18 +00:00
committed by GitHub
parent c1492aab75
commit bb199f6226
9 changed files with 80 additions and 104 deletions
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toolchain/check/handle_impl.cpp
+12 -4
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@@ -250,12 +250,19 @@ static auto BuildImplDecl(Context& context, Parse::AnyImplDeclId node_id,
// This requires that the facet type is identified, and returns the single
// interface from the identified facet type. It returns None if an error was
// diagnosed.
auto specific_interface = CheckConstraintIsInterface(
auto identified_id = CheckConstraintIsInterface(
context, node_id, self_type_inst_id, full_constraint_type_inst_id);
if (!specific_interface.interface_id.has_value()) {
if (!identified_id.has_value()) {
full_constraint_type_inst_id = SemIR::ErrorInst::TypeInstId;
}
auto specific_interface =
full_constraint_type_inst_id != SemIR::ErrorInst::InstId
? context.identified_facet_types()
.Get(identified_id)
.impl_as_target_interface()
: SemIR::SpecificInterface::None;
// Store an instruction in the decl's eval block that contains the target
// interface's specific, whose constant value will be updated when specifics
// are applied to the impl.
@@ -268,7 +275,7 @@ static auto BuildImplDecl(Context& context, Parse::AnyImplDeclId node_id,
// we introduced a new instruction with a SpecificId operand instead of
// reusing ImplSelfWitness for this.
auto interface_inst_id =
specific_interface.interface_id.has_value()
full_constraint_type_inst_id != SemIR::ErrorInst::InstId
? AddInst<SemIR::ImplSelfWitness>(
context, node_id,
{.type_id =
@@ -407,7 +414,8 @@ static auto BuildImplDecl(Context& context, Parse::AnyImplDeclId node_id,
// also must be part of the generic eval block by coming before
// FinishGenericDecl().
impl.witness_id = AddImplWitnessForDeclaration(
context, node_id, impl, full_constraint_type_inst_id,
context, node_id, SemIR::LocId(full_constraint_type_inst_id),
impl, identified_id,
context.generics().GetSelfSpecific(impl.generic_id));
impl.witness_block_id = context.inst_block_stack().Pop();