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Only propagate .Self dependence in facet types from extended constraints (#7253)

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When forming the constant value of a `where` expression, don't consider
it to be `.Self`-dependent if the dependence only comes from the RHS of
the `where`. More generally, ignore `.Self` dependence when evaluating a
facet type unless it comes from an extended interface or named
constraint. While we can get other kinds of constraint from the
left-hand side of a `where`, such constraints must either come from the
right-hand side of other `where` expressions or be extend constraints.

This fixes a crash in lowering caused by a concrete function containing
a `.Self`-symbolic `where` constant.

Assisted-by: Gemini via Antigravity
This commit is contained in:
Richard Smith
2026-05-27 22:04:48 +00:00
committed by GitHub
parent 7569aff619
commit 9986d0da69
9 changed files with 254 additions and 87 deletions
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toolchain/check/eval.cpp
+22 -40
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@@ -475,33 +475,6 @@ static auto RequireConstantValue(EvalContext& eval_context,
return SemIR::ErrorInst::InstId;
}
// If the given instruction is constant, returns its constant value. Otherwise,
// produces an error diagnostic. When determining the phase of the result,
// ignore any dependence on `.Self`.
//
// This is used when evaluating facet types, for which `where` expressions using
// `.Self` should not be considered symbolic
// - `Interface where .Self impls I and .A = bool` -> concrete
// - `T:! type` ... `Interface where .A = T` -> symbolic, since uses `T` which
// is symbolic and not due to `.Self`.
static auto RequireConstantValueIgnoringPeriodSelf(EvalContext& eval_context,
SemIR::InstId inst_id,
Phase* phase)
-> SemIR::InstId {
if (!inst_id.has_value()) {
return SemIR::InstId::None;
}
Phase constant_phase = *phase;
auto const_inst_id =
RequireConstantValue(eval_context, inst_id, &constant_phase);
// Since LatestPhase(x, Phase::Concrete) == x, this is equivalent to replacing
// Phase::PeriodSelfSymbolic with Phase::Concrete.
if (constant_phase != Phase::PeriodSelfSymbolic) {
*phase = LatestPhase(*phase, constant_phase);
}
return const_inst_id;
}
// Gets a constant value for an `inst_id`, diagnosing when the input is not
// constant, and CHECKing that it is concrete. Should only be used in contexts
// where non-concrete constants cannot appear.
@@ -723,6 +696,10 @@ static auto GetConstantFacetTypeInfo(EvalContext& eval_context,
Phase* phase) -> SemIR::FacetTypeInfo {
SemIR::FacetTypeInfo info = {};
// Phase of constraints whose `.Self` refers to the type constrained by this
// facet type.
Phase self_phase = Phase::Concrete;
info.extend_constraints.reserve(orig.extend_constraints.size());
for (const auto& extend : orig.extend_constraints) {
// TODO: Add GetConstantValue for SpecificInterface.
@@ -737,8 +714,8 @@ static auto GetConstantFacetTypeInfo(EvalContext& eval_context,
// TODO: Add GetConstantValue for SpecificInterface.
info.self_impls_constraints.push_back(
{.interface_id = self_impls.interface_id,
.specific_id =
GetConstantValue(eval_context, self_impls.specific_id, phase)});
.specific_id = GetConstantValue(eval_context, self_impls.specific_id,
&self_phase)});
}
info.extend_named_constraints.reserve(orig.extend_named_constraints.size());
@@ -756,21 +733,21 @@ static auto GetConstantFacetTypeInfo(EvalContext& eval_context,
// TODO: Add GetConstantValue for SpecificNamedConstraint.
info.self_impls_named_constraints.push_back(
{.named_constraint_id = self_impls.named_constraint_id,
.specific_id =
GetConstantValue(eval_context, self_impls.specific_id, phase)});
.specific_id = GetConstantValue(eval_context, self_impls.specific_id,
&self_phase)});
}
info.type_impls_interfaces.reserve(orig.type_impls_interfaces.size());
for (const auto& type_impls : orig.type_impls_interfaces) {
info.type_impls_interfaces.push_back(
{.self_type =
GetConstantValue(eval_context, type_impls.self_type, phase),
GetConstantValue(eval_context, type_impls.self_type, &self_phase),
// TODO: Add GetConstantValue for SpecificInterface.
.specific_interface = {
.interface_id = type_impls.specific_interface.interface_id,
.specific_id = GetConstantValue(
eval_context, type_impls.specific_interface.specific_id,
phase)}});
&self_phase)}});
}
info.type_impls_named_constraints.reserve(
@@ -778,14 +755,14 @@ static auto GetConstantFacetTypeInfo(EvalContext& eval_context,
for (const auto& type_impls : orig.type_impls_named_constraints) {
info.type_impls_named_constraints.push_back(
{.self_type =
GetConstantValue(eval_context, type_impls.self_type, phase),
GetConstantValue(eval_context, type_impls.self_type, &self_phase),
// TODO: Add GetConstantValue for SpecificNamedConstraint.
.specific_named_constraint = {
.named_constraint_id =
type_impls.specific_named_constraint.named_constraint_id,
.specific_id = GetConstantValue(
eval_context, type_impls.specific_named_constraint.specific_id,
phase)}});
&self_phase)}});
}
// Rewrite constraints are resolved first before replacing them with their
@@ -806,14 +783,19 @@ static auto GetConstantFacetTypeInfo(EvalContext& eval_context,
}
for (auto& rewrite : info.rewrite_constraints) {
// `where` requirements using `.Self` should not be considered symbolic.
auto lhs_id = RequireConstantValueIgnoringPeriodSelf(eval_context,
rewrite.lhs_id, phase);
auto rhs_id = RequireConstantValueIgnoringPeriodSelf(eval_context,
rewrite.rhs_id, phase);
auto lhs_id =
RequireConstantValue(eval_context, rewrite.lhs_id, &self_phase);
auto rhs_id =
RequireConstantValue(eval_context, rewrite.rhs_id, &self_phase);
rewrite = {.lhs_id = lhs_id, .rhs_id = rhs_id};
}
// Update phase, ignoring `.Self` dependence from constraints whose `.Self` is
// scoped to this facet type.
if (self_phase > Phase::PeriodSelfSymbolic) {
*phase = LatestPhase(*phase, self_phase);
}
// TODO: Process other requirements.
info.other_requirements = orig.other_requirements;