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Avoid symbolic witnesses for .Self in an impl decl (#7564)

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Point symbolic witnesses into `.Self` written inside an impl decl at the
impl that is being declared. This is tricky because the impl does not
yet exist. So we use a new instruction `ImplSelfWitness` which _will_ be
replaced by the `ImplWitness` once it becomes available. The
`ImplSelfWitness` acts like a symbolic witness, except it does not
perform lookup, since we know which impl we will get a witness from.

This prevents us from finding other impls when performing lookups into
`.Self` in an impl decl, which produces incorrect/incoherent results.
This commit is contained in:
Dana Jansens
2026-07-29 16:25:23 +00:00
committed by GitHub
parent 2ac425e591
commit f51c075f8b
94 changed files with 3221 additions and 2797 deletions
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toolchain/check/handle_impl.cpp
+44 -27
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@@ -108,6 +108,10 @@ auto HandleParseNode(Context& context, Parse::ImplTypeAsId node_id) -> bool {
// TODO: Revisit this once #3714 is resolved.
AddNameToLookup(context, SemIR::NameId::SelfType, self_type.inst_id);
context.node_stack().Push(node_id, self_type.inst_id);
// The value in here, if any, is populated by the `where` expression that
// introduces a `.Self` in the impl's constraint facet type.
context.declaring_impl_decls().push_back(SemIR::SpecificInterface::None);
return true;
}
@@ -140,6 +144,10 @@ auto HandleParseNode(Context& context, Parse::ImplDefaultSelfAsId node_id)
// There's no need to push `Self` into scope here, because we can find it in
// the parent class scope.
context.node_stack().Push(node_id, self_inst_id);
// The value in here, if any, is populated by the `where` expression that
// introduces a `.Self` in the impl's constraint facet type.
context.declaring_impl_decls().push_back(SemIR::SpecificInterface::None);
return true;
}
@@ -197,7 +205,7 @@ static auto PopImplIntroducerAndParamsAsNameComponent(
// also sets the `definition_id` on the Impl structure.
static auto BuildImplDecl(Context& context, Parse::AnyImplDeclId node_id,
bool has_definition)
-> std::pair<SemIR::ImplId, SemIR::InstId> {
-> std::tuple<SemIR::ImplId, SemIR::InstId, SemIR::TypeInstId> {
auto [constraint_node, constraint_id] =
context.node_stack().PopExprWithNodeId();
auto [self_type_node, self_type_inst_id] =
@@ -206,9 +214,10 @@ static auto BuildImplDecl(Context& context, Parse::AnyImplDeclId node_id,
auto name = PopImplIntroducerAndParamsAsNameComponent(context, node_id);
auto decl_block_id = context.inst_block_stack().Pop();
// Convert the constraint expression to a type.
auto [constraint_type_inst_id, constraint_type_id] =
ExprAsType(context, constraint_node, constraint_id);
// Convert the constraint expression to a type. This contains all constraints,
// including rewrites and other constrains on the RHS of `where`.
auto full_constraint_type_inst_id =
ExprAsType(context, constraint_node, constraint_id).inst_id;
// Process modifiers.
// TODO: Should we somehow permit access specifiers on `impl`s?
@@ -229,30 +238,35 @@ static auto BuildImplDecl(Context& context, Parse::AnyImplDeclId node_id,
SemIR::ImplDecl{.impl_id = SemIR::ImplId::None,
.decl_block_id = decl_block_id});
if (!CheckConstraintIsFacetType(context, node_id, constraint_type_inst_id)) {
constraint_type_inst_id = SemIR::ErrorInst::TypeInstId;
if (!CheckConstraintIsFacetType(context, node_id,
full_constraint_type_inst_id)) {
full_constraint_type_inst_id = SemIR::ErrorInst::TypeInstId;
}
// The identified facet type will also replace `.Self` references in the
// specific interface, but we want to store the full facet type not just the
// identified one. So we have to replace `.Self` references explicitly here in
// the constraint.
//
// We do this after `CheckConstraintIsFacetType()` which has ensured the
// constraint is in fact a FacetType. We do this before identifying the facet
// type in `CheckConstraintIsInterface()` so that the identified facet type is
// for the substituted facet type instruction that will be stored in the Impl.
// This ensures the impl bucket finds the identified facet type.
constraint_type_inst_id = SubstPeriodSelfInFacetType(
context, constraint_node, self_type_inst_id, constraint_type_inst_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(
context, node_id, self_type_inst_id, constraint_type_inst_id);
context, node_id, self_type_inst_id, full_constraint_type_inst_id);
if (!specific_interface.interface_id.has_value()) {
constraint_type_inst_id = SemIR::ErrorInst::TypeInstId;
full_constraint_type_inst_id = SemIR::ErrorInst::TypeInstId;
}
// Strip off anything on the RHS of `where`, as they are not part of the
// constraint being implemented, they just represent requirements that must be
// met when the impl is defined. This drops any `.Self` references from the
// resulting impl's `constraint_id` as they don't make sense outside the scope
// of the impl declaration.
auto extend_constraint_type_inst_id = full_constraint_type_inst_id;
if (auto where = context.insts().TryGetAs<SemIR::WhereExpr>(
extend_constraint_type_inst_id)) {
for (auto req_id : context.inst_blocks().Get(where->requirements_id)) {
if (auto base = context.insts().TryGetAs<SemIR::RequirementBaseFacetType>(
req_id)) {
extend_constraint_type_inst_id = base->base_type_inst_id;
break;
}
}
}
// The impl decl has a scope stack entry for the DeclNameStack, so we look at
@@ -267,7 +281,7 @@ static auto BuildImplDecl(Context& context, Parse::AnyImplDeclId node_id,
{.parent_scope_inst_id = parent_scope_inst_id,
.is_final = is_final,
.self_id = self_type_inst_id,
.constraint_id = constraint_type_inst_id,
.constraint_id = extend_constraint_type_inst_id,
.interface = specific_interface}};
if (has_definition) {
impl.definition_id = impl_decl_id;
@@ -366,7 +380,7 @@ 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,
context, node_id, impl, full_constraint_type_inst_id,
context.generics().GetSelfSpecific(impl.generic_id));
impl.witness_block_id = context.inst_block_stack().Pop();
@@ -395,14 +409,15 @@ static auto BuildImplDecl(Context& context, Parse::AnyImplDeclId node_id,
impl_decl.impl_id = impl_id;
ReplaceInstBeforeConstantUse(context, impl_decl_id, impl_decl);
return {impl_id, impl_decl_id};
return {impl_id, impl_decl_id, full_constraint_type_inst_id};
}
auto HandleParseNode(Context& context, Parse::ImplDeclId node_id) -> bool {
auto [impl_id, impl_decl_id] = BuildImplDecl(context, node_id, false);
auto [impl_id, impl_decl_id, _] = BuildImplDecl(context, node_id, false);
auto& impl = context.impls().Get(impl_id);
context.decl_name_stack().PopScope();
context.declaring_impl_decls().pop_back();
// Impl definitions are required in the same file as the declaration. We skip
// this requirement if we've already issued an invalid redeclaration error, or
@@ -416,7 +431,8 @@ auto HandleParseNode(Context& context, Parse::ImplDeclId node_id) -> bool {
auto HandleParseNode(Context& context, Parse::ImplDefinitionStartId node_id)
-> bool {
auto [impl_id, impl_decl_id] = BuildImplDecl(context, node_id, true);
auto [impl_id, impl_decl_id, full_constraint_id] =
BuildImplDecl(context, node_id, true);
auto& impl = context.impls().Get(impl_id);
impl.scope_id =
@@ -430,9 +446,10 @@ auto HandleParseNode(Context& context, Parse::ImplDefinitionStartId node_id)
context.generics().GetSelfSpecific(impl.generic_id));
StartGenericDefinition(context, impl.generic_id);
ImplWitnessStartDefinition(context, impl);
CheckRequireDeclsSatisfied(context, node_id, impl);
CheckRequireDeclsSatisfied(context, node_id, impl, full_constraint_id);
context.inst_block_stack().Push();
context.node_stack().Push(node_id, impl_id);
context.declaring_impl_decls().pop_back();
// TODO: Handle the case where there's control flow in the impl body. For
// example: