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Rearrange convert: construct FacetAccessType from a facet value before impl lookup instead of after (#6113)

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This makes convert more consistent, it always makes a FacetAccessType
for a facet value, rather than only doing so after lookup returns. The
intention for this is that FacetAccessType will evaluate to
SymbolicBindingType in the future, so this will expose that constant
value to impl lookup instead of the original facet value, which will
avoid impl lookup having to deal with `.Self` or `BindSymbolicName`
specifically.
This commit is contained in:
Dana Jansens
2025-09-29 22:49:06 +00:00
committed by GitHub
parent 5abd214d9d
commit a6bb11f1cf
36 changed files with 158 additions and 125 deletions
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toolchain/check/convert.cpp
+27 -25
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@@ -1198,19 +1198,24 @@ static auto PerformBuiltinConversion(
if (sem_ir.types().Is<SemIR::FacetType>(target.type_id) &&
(sem_ir.types().Is<SemIR::TypeType>(value_type_id) ||
sem_ir.types().Is<SemIR::FacetType>(value_type_id))) {
// The value is a type or facet value, so it has a constant value. We get
// that to unwrap things like NameRef and get to the underlying type or
// facet value instruction so that we can use `TryGetAs`.
auto const_value_id = sem_ir.constant_values().GetConstantInstId(value_id);
// TODO: Runtime facet values should be allowed to convert based on their
// FacetTypes, but we assume constant values for impl lookup at the moment.
if (!const_value_id.has_value()) {
if (!context.constant_values().Get(value_id).is_constant()) {
context.TODO(loc_id, "conversion of runtime facet value");
const_value_id = SemIR::ErrorInst::InstId;
return SemIR::ErrorInst::InstId;
}
if (auto facet_access_type_inst =
sem_ir.insts().TryGetAs<SemIR::FacetAccessType>(const_value_id)) {
// Get the canonical type for which we want to attach a new set of witnesses
// to match the requirements of the target FacetType.
auto type_inst_id = SemIR::TypeInstId::None;
if (sem_ir.types().Is<SemIR::FacetType>(value_type_id)) {
type_inst_id = AddTypeInst<SemIR::FacetAccessType>(
context, loc_id,
{.type_id = SemIR::TypeType::TypeId,
.facet_value_inst_id = value_id});
} else {
type_inst_id = context.types().GetAsTypeInstId(value_id);
// Shortcut for lossless round trips through a FacetAccessType when
// converting back to the type of its original facet value.
//
@@ -1222,9 +1227,19 @@ static auto PerformBuiltinConversion(
//
// See also test:
// facet_access_type_converts_back_to_original_facet_value.carbon
auto facet_value_inst_id = facet_access_type_inst->facet_value_inst_id;
if (sem_ir.insts().Get(facet_value_inst_id).type_id() == target.type_id) {
return facet_value_inst_id;
//
// TODO: This instruction is going to become a `SymbolicBindingType`, so
// we'll need to handle that instead.
auto const_type_inst_id =
sem_ir.constant_values().GetConstantTypeInstId(type_inst_id);
if (auto facet_access_type_inst =
sem_ir.insts().TryGetAs<SemIR::FacetAccessType>(
const_type_inst_id)) {
auto facet_value_inst_id = facet_access_type_inst->facet_value_inst_id;
if (sem_ir.insts().Get(facet_value_inst_id).type_id() ==
target.type_id) {
return facet_value_inst_id;
}
}
}
@@ -1233,25 +1248,12 @@ static auto PerformBuiltinConversion(
// type satisfies the requirements of the target `FacetType`, as determined
// by finding impl witnesses for the target FacetType.
auto lookup_result = LookupImplWitness(
context, loc_id, sem_ir.constant_values().Get(const_value_id),
context, loc_id, sem_ir.constant_values().Get(type_inst_id),
sem_ir.types().GetConstantId(target.type_id));
if (lookup_result.has_value()) {
if (lookup_result.has_error_value()) {
return SemIR::ErrorInst::InstId;
} else {
// We bind the input value to the target `FacetType` with a
// `FacetValue`, which requires an instruction of type `TypeType`. So if
// we are converting from a facet value, we get its `type` via an extra
// `FacetAccessType` instruction.
auto type_inst_id = SemIR::TypeInstId::None;
if (sem_ir.types().Is<SemIR::FacetType>(value_type_id)) {
type_inst_id = AddTypeInst<SemIR::FacetAccessType>(
context, loc_id,
{.type_id = SemIR::TypeType::TypeId,
.facet_value_inst_id = const_value_id});
} else {
type_inst_id = context.types().GetAsTypeInstId(const_value_id);
}
// Note that `FacetValue`'s type is the same `FacetType` that was used
// to construct the set of witnesses, ie. the query to
// `LookupImplWitness()`. This ensures that the witnesses are in the