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848eddc9dd97a39bdf768d3b56fdfbe0fc4af862
carbon-lang/toolchain/check/impl.cpp
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Dana Jansens 848eddc9dd Avoid cyclic lookup of an impl inside its own definition (#6629) 
An interface A requiring another interface B means that an impl of A
must verify that the self-type also impls B. The instructions created
from this can involved a lookup that the self-type impls A, which end up
finding the impl being defined. This is not problematic of itself, but
it is problematic if these lookup instructions become part of the impl's
generic definition. When we find a specific of that `impl as A` during
impl lookup of A, and we resolve the specific definition, those lookup
instructions are replayed. Doing so does another lookup for `impl as A`,
which creates an infinitely recursive loop.

To break this loop we move the lookup instructions done to verify that
the self-type impls B outside of the definition of `impl as A`. This
prevents them from being specialized. But it doesn't prevent us from
diagnosing monomorphization errors properly. They just get diagnosed at
the use of that invalid specific, instead of inside the verification of
`impl as B` in the definition of `impl as A`.
2026-01-20 19:28:46 +00:00

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// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "toolchain/check/impl.h"
#include "toolchain/base/kind_switch.h"
#include "toolchain/check/context.h"
#include "toolchain/check/convert.h"
#include "toolchain/check/deduce.h"
#include "toolchain/check/eval.h"
#include "toolchain/check/facet_type.h"
#include "toolchain/check/function.h"
#include "toolchain/check/generic.h"
#include "toolchain/check/impl_lookup.h"
#include "toolchain/check/import_ref.h"
#include "toolchain/check/inst.h"
#include "toolchain/check/interface.h"
#include "toolchain/check/merge.h"
#include "toolchain/check/name_lookup.h"
#include "toolchain/check/name_scope.h"
#include "toolchain/check/require_impls.h"
#include "toolchain/check/thunk.h"
#include "toolchain/check/type.h"
#include "toolchain/check/type_completion.h"
#include "toolchain/check/type_structure.h"
#include "toolchain/diagnostics/diagnostic_emitter.h"
#include "toolchain/sem_ir/generic.h"
#include "toolchain/sem_ir/ids.h"
#include "toolchain/sem_ir/impl.h"
#include "toolchain/sem_ir/inst.h"
#include "toolchain/sem_ir/typed_insts.h"
namespace Carbon::Check {
// Adds the location of the associated function to a diagnostic.
static auto NoteAssociatedFunction(Context& context, DiagnosticBuilder& builder,
SemIR::FunctionId function_id) -> void {
CARBON_DIAGNOSTIC(AssociatedFunctionHere, Note,
"associated function {0} declared here", SemIR::NameId);
const auto& function = context.functions().Get(function_id);
builder.Note(function.latest_decl_id(), AssociatedFunctionHere,
function.name_id);
}
auto CheckAssociatedFunctionImplementation(
Context& context, SemIR::FunctionType interface_function_type,
SemIR::SpecificId enclosing_specific_id, SemIR::InstId impl_decl_id,
SemIR::TypeId self_type_id, SemIR::InstId witness_inst_id,
bool defer_thunk_definition) -> SemIR::InstId {
auto impl_function_decl =
context.insts().TryGetAs<SemIR::FunctionDecl>(impl_decl_id);
if (!impl_function_decl) {
if (impl_decl_id != SemIR::ErrorInst::InstId) {
CARBON_DIAGNOSTIC(ImplFunctionWithNonFunction, Error,
"associated function {0} implemented by non-function",
SemIR::NameId);
auto builder = context.emitter().Build(
impl_decl_id, ImplFunctionWithNonFunction,
context.functions().Get(interface_function_type.function_id).name_id);
NoteAssociatedFunction(context, builder,
interface_function_type.function_id);
builder.Emit();
}
return SemIR::ErrorInst::InstId;
}
// Map from the specific for the function type to the specific for the
// function signature. The function signature may have additional generic
// parameters.
auto interface_function_specific_id =
GetSelfSpecificForInterfaceMemberWithSelfType(
context, SemIR::LocId(impl_decl_id),
interface_function_type.specific_id,
context.functions()
.Get(interface_function_type.function_id)
.generic_id,
enclosing_specific_id, self_type_id, witness_inst_id);
return BuildThunk(context, interface_function_type.function_id,
interface_function_specific_id, impl_decl_id,
defer_thunk_definition);
}
// Returns true if impl redeclaration parameters match.
static auto CheckImplRedeclParamsMatch(Context& context,
const SemIR::Impl& new_impl,
SemIR::ImplId prev_impl_id) -> bool {
auto& prev_impl = context.impls().Get(prev_impl_id);
// If the parameters aren't the same, then this is not a redeclaration of this
// `impl`. Keep looking for a prior declaration without issuing a diagnostic.
if (!CheckRedeclParamsMatch(context, DeclParams(new_impl),
DeclParams(prev_impl), SemIR::SpecificId::None,
/*diagnose=*/false, /*check_syntax=*/true,
/*check_self=*/true)) {
// NOLINTNEXTLINE(readability-simplify-boolean-expr)
return false;
}
return true;
}
// Returns whether an impl can be redeclared. For example, defined impls
// cannot be redeclared.
static auto IsValidImplRedecl(Context& context, const SemIR::Impl& new_impl,
SemIR::ImplId prev_impl_id) -> bool {
auto& prev_impl = context.impls().Get(prev_impl_id);
// TODO: Following #3763, disallow redeclarations in different scopes.
// Following #4672, disallowing defining non-extern declarations in another
// file.
if (auto import_ref =
context.insts().TryGetAs<SemIR::AnyImportRef>(prev_impl.self_id)) {
// TODO: Handle extern.
CARBON_DIAGNOSTIC(RedeclImportedImpl, Error,
"redeclaration of imported impl");
// TODO: Note imported declaration
context.emitter().Emit(new_impl.latest_decl_id(), RedeclImportedImpl);
return false;
}
if (prev_impl.has_definition_started()) {
// Impls aren't merged in order to avoid generic region lookup into a
// mismatching table.
CARBON_DIAGNOSTIC(ImplRedefinition, Error,
"redefinition of `impl {0} as {1}`", InstIdAsRawType,
InstIdAsRawType);
CARBON_DIAGNOSTIC(ImplPreviousDefinition, Note,
"previous definition was here");
context.emitter()
.Build(new_impl.latest_decl_id(), ImplRedefinition, new_impl.self_id,
new_impl.constraint_id)
.Note(prev_impl.definition_id, ImplPreviousDefinition)
.Emit();
return false;
}
// TODO: Only allow redeclaration in a match_first/impl_priority block.
return true;
}
// Looks for any unused generic bindings. If one is found, it is diagnosed and
// false is returned.
static auto VerifyAllGenericBindingsUsed(Context& context, SemIR::LocId loc_id,
SemIR::LocId implicit_params_loc_id,
SemIR::Impl& impl) -> bool {
if (impl.witness_id == SemIR::ErrorInst::InstId) {
return true;
}
if (!impl.generic_id.has_value()) {
return true;
}
if (impl.implicit_param_patterns_id.has_value()) {
for (auto inst_id :
context.inst_blocks().Get(impl.implicit_param_patterns_id)) {
if (inst_id == SemIR::ErrorInst::InstId) {
// An error was already diagnosed for a generic binding.
return true;
}
}
}
auto deduced_specific_id = DeduceImplArguments(
context, loc_id, impl, context.constant_values().Get(impl.self_id),
impl.interface.specific_id);
if (deduced_specific_id.has_value()) {
// Deduction succeeded, all bindings were used.
return true;
}
CARBON_DIAGNOSTIC(ImplUnusedBinding, Error,
"`impl` with unused generic binding");
// TODO: This location may be incorrect, the binding may be inherited
// from an outer declaration. It would be nice to get the particular
// binding that was undeducible back from DeduceImplArguments here and
// use that.
auto diag_loc_id =
implicit_params_loc_id.has_value() ? implicit_params_loc_id : loc_id;
context.emitter().Emit(diag_loc_id, ImplUnusedBinding);
return false;
}
// Apply an `extend impl` declaration by extending the parent scope with the
// `impl`. If there's an error it is diagnosed and false is returned.
static auto ApplyExtendImplAs(Context& context, SemIR::LocId loc_id,
const SemIR::Impl& impl,
Parse::NodeId extend_node,
SemIR::LocId implicit_params_loc_id) -> bool {
auto parent_scope_id = context.decl_name_stack().PeekParentScopeId();
// TODO: Also handle the parent scope being a mixin.
auto class_scope = TryAsClassScope(context, parent_scope_id);
if (!class_scope) {
if (impl.witness_id != SemIR::ErrorInst::InstId) {
CARBON_DIAGNOSTIC(
ExtendImplOutsideClass, Error,
"`extend impl` can only be used in an interface or class");
context.emitter().Emit(loc_id, ExtendImplOutsideClass);
}
return false;
}
auto& parent_scope = *class_scope->name_scope;
// An error was already diagnosed, but this is `extend impl as` inside a
// class, so propagate the error into the enclosing class scope.
if (impl.witness_id == SemIR::ErrorInst::InstId) {
parent_scope.set_has_error();
return false;
}
if (implicit_params_loc_id.has_value()) {
CARBON_DIAGNOSTIC(ExtendImplForall, Error,
"cannot `extend` a parameterized `impl`");
context.emitter().Emit(extend_node, ExtendImplForall);
parent_scope.set_has_error();
return false;
}
if (!RequireCompleteType(
context, context.types().GetTypeIdForTypeInstId(impl.constraint_id),
SemIR::LocId(impl.constraint_id), [&] {
CARBON_DIAGNOSTIC(ExtendImplAsIncomplete, Error,
"`extend impl as` incomplete facet type {0}",
InstIdAsType);
return context.emitter().Build(impl.latest_decl_id(),
ExtendImplAsIncomplete,
impl.constraint_id);
})) {
parent_scope.set_has_error();
return false;
}
if (!impl.generic_id.has_value()) {
parent_scope.AddExtendedScope(impl.constraint_id);
} else {
auto constraint_id_in_self_specific = AddTypeInst<SemIR::SpecificConstant>(
context, SemIR::LocId(impl.constraint_id),
{.type_id = SemIR::TypeType::TypeId,
.inst_id = impl.constraint_id,
.specific_id = context.generics().GetSelfSpecific(impl.generic_id)});
parent_scope.AddExtendedScope(constraint_id_in_self_specific);
}
return true;
}
auto FindImplId(Context& context, const SemIR::Impl& query_impl)
-> std::variant<RedeclaredImpl, NewImpl> {
// Look for an existing matching declaration.
auto lookup_bucket_ref = context.impls().GetOrAddLookupBucket(query_impl);
// TODO: Detect two impl declarations with the same self type and interface,
// and issue an error if they don't match.
for (auto prev_impl_id : lookup_bucket_ref) {
if (CheckImplRedeclParamsMatch(context, query_impl, prev_impl_id)) {
if (IsValidImplRedecl(context, query_impl, prev_impl_id)) {
return RedeclaredImpl{.prev_impl_id = prev_impl_id};
} else {
// IsValidImplRedecl() has issued a diagnostic, take care to avoid
// generating more diagnostics for this declaration.
return NewImpl{.lookup_bucket = lookup_bucket_ref,
.find_had_error = true};
}
break;
}
}
return NewImpl{.lookup_bucket = lookup_bucket_ref, .find_had_error = false};
}
// Sets the `ImplId` in the `ImplWitnessTable`.
static auto AssignImplIdInWitness(Context& context, SemIR::ImplId impl_id,
SemIR::InstId witness_id) -> void {
if (witness_id == SemIR::ErrorInst::InstId) {
return;
}
auto witness = context.insts().GetAs<SemIR::ImplWitness>(witness_id);
auto witness_table =
context.insts().GetAs<SemIR::ImplWitnessTable>(witness.witness_table_id);
witness_table.impl_id = impl_id;
// Note: The `ImplWitnessTable` instruction is `Unique`, so while this marks
// the instruction as being a dependent instruction of a generic impl, it will
// not be substituted into the eval block.
ReplaceInstBeforeConstantUse(context, witness.witness_table_id,
witness_table);
}
auto AddImpl(Context& context, const SemIR::Impl& impl,
SemIR::ImplStore::LookupBucketRef lookup_bucket,
Parse::NodeId extend_node, SemIR::LocId implicit_params_loc_id)
-> SemIR::ImplId {
auto impl_decl_id = impl.latest_decl_id();
// From here on, use the `Impl` from the `ImplStore` instead of `impl` in
// order to make and see any changes to the `Impl`.
auto impl_id = context.impls().Add(impl);
lookup_bucket.push_back(impl_id);
AssignImplIdInWitness(context, impl_id, impl.witness_id);
auto& stored_impl = context.impls().Get(impl_id);
// Look to see if there are any generic bindings on the `impl` declaration
// that are not deducible. If so, and the `impl` does not actually use all
// its generic bindings, and will never be matched. This should be
// diagnossed to the user.
if (!VerifyAllGenericBindingsUsed(context, SemIR::LocId(impl_decl_id),
implicit_params_loc_id, stored_impl)) {
FillImplWitnessWithErrors(context, stored_impl);
}
if (extend_node.has_value()) {
if (!ApplyExtendImplAs(context, SemIR::LocId(impl_decl_id), stored_impl,
extend_node, implicit_params_loc_id)) {
FillImplWitnessWithErrors(context, stored_impl);
}
}
return impl_id;
}
// Returns whether the `LookupImplWitness` of `witness_id` matches `interface`.
static auto WitnessQueryMatchesInterface(
Context& context, SemIR::InstId witness_id,
const SemIR::SpecificInterface& interface) -> bool {
auto lookup = context.insts().GetAs<SemIR::LookupImplWitness>(witness_id);
return interface ==
context.specific_interfaces().Get(lookup.query_specific_interface_id);
}
auto AddImplWitnessForDeclaration(Context& context, SemIR::LocId loc_id,
const SemIR::Impl& impl,
SemIR::SpecificId self_specific_id)
-> SemIR::InstId {
auto facet_type_id =
context.types().GetTypeIdForTypeInstId(impl.constraint_id);
CARBON_CHECK(facet_type_id != SemIR::ErrorInst::TypeId);
auto facet_type = context.types().GetAs<SemIR::FacetType>(facet_type_id);
const auto& facet_type_info =
context.facet_types().Get(facet_type.facet_type_id);
// An iterator over the rewrite_constraints where the LHS of the rewrite names
// a member of the `impl.interface`. This filters out rewrites of names
// from other interfaces, as they do not set values in the witness table.
auto rewrites_into_interface_to_witness = llvm::make_filter_range(
facet_type_info.rewrite_constraints,
[&](const SemIR::FacetTypeInfo::RewriteConstraint& rewrite) {
auto access = context.insts().GetAs<SemIR::ImplWitnessAccess>(
GetImplWitnessAccessWithoutSubstitution(context, rewrite.lhs_id));
return WitnessQueryMatchesInterface(context, access.witness_id,
impl.interface);
});
if (rewrites_into_interface_to_witness.empty()) {
// The witness table is not needed until the definition. Make a placeholder
// for the declaration.
auto witness_table_inst_id = AddInst<SemIR::ImplWitnessTable>(
context, loc_id,
{.elements_id = context.inst_blocks().AddPlaceholder(),
.impl_id = SemIR::ImplId::None});
return AddInst<SemIR::ImplWitness>(
context, loc_id,
{.type_id = GetSingletonType(context, SemIR::WitnessType::TypeInstId),
.witness_table_id = witness_table_inst_id,
.specific_id = self_specific_id});
}
const auto& interface = context.interfaces().Get(impl.interface.interface_id);
if (!interface.is_complete()) {
// This is a declaration with rewrite constraints into `.Self`, but the
// interface is not complete. Those rewrites have already been diagnosed as
// an error in their member access.
return SemIR::ErrorInst::InstId;
}
auto assoc_entities =
context.inst_blocks().Get(interface.associated_entities_id);
// TODO: When this function is used for things other than just impls, may want
// to only load the specific associated entities that are mentioned in rewrite
// rules.
for (auto decl_id : assoc_entities) {
LoadImportRef(context, decl_id);
}
SemIR::InstId witness_inst_id = SemIR::InstId::None;
llvm::MutableArrayRef<SemIR::InstId> table;
{
auto elements_id =
context.inst_blocks().AddUninitialized(assoc_entities.size());
table = context.inst_blocks().GetMutable(elements_id);
for (auto& uninit : table) {
uninit = SemIR::InstId::ImplWitnessTablePlaceholder;
}
auto witness_table_inst_id = AddInst<SemIR::ImplWitnessTable>(
context, loc_id,
{.elements_id = elements_id, .impl_id = SemIR::ImplId::None});
witness_inst_id = AddInst<SemIR::ImplWitness>(
context, loc_id,
{.type_id = GetSingletonType(context, SemIR::WitnessType::TypeInstId),
.witness_table_id = witness_table_inst_id,
.specific_id = self_specific_id});
}
for (auto rewrite : rewrites_into_interface_to_witness) {
auto access = context.insts().GetAs<SemIR::ImplWitnessAccess>(
GetImplWitnessAccessWithoutSubstitution(context, rewrite.lhs_id));
auto& table_entry = table[access.index.index];
if (table_entry == SemIR::ErrorInst::InstId) {
// Don't overwrite an error value. This prioritizes not generating
// multiple errors for one associated constant over picking a value
// for it to use to attempt recovery.
continue;
}
auto rewrite_inst_id = rewrite.rhs_id;
if (rewrite_inst_id == SemIR::ErrorInst::InstId) {
table_entry = SemIR::ErrorInst::InstId;
continue;
}
auto decl_id = context.constant_values().GetConstantInstId(
assoc_entities[access.index.index]);
CARBON_CHECK(decl_id.has_value(), "Non-constant associated entity");
if (decl_id == SemIR::ErrorInst::InstId) {
table_entry = SemIR::ErrorInst::InstId;
continue;
}
auto assoc_constant_decl =
context.insts().TryGetAs<SemIR::AssociatedConstantDecl>(decl_id);
if (!assoc_constant_decl) {
auto type_id = context.insts().Get(decl_id).type_id();
auto type_inst = context.types().GetAsInst(type_id);
auto fn_type = type_inst.As<SemIR::FunctionType>();
const auto& fn = context.functions().Get(fn_type.function_id);
CARBON_DIAGNOSTIC(RewriteForAssociatedFunction, Error,
"rewrite specified for associated function {0}",
SemIR::NameId);
context.emitter().Emit(impl.constraint_id, RewriteForAssociatedFunction,
fn.name_id);
table_entry = SemIR::ErrorInst::InstId;
continue;
}
// FacetTypes resolution disallows two rewrites to the same associated
// constant, so we won't ever have a facet write twice to the same position
// in the witness table.
CARBON_CHECK(table_entry == SemIR::InstId::ImplWitnessTablePlaceholder);
// If the associated constant has a symbolic type, convert the rewrite
// value to that type now we know the value of `Self`.
SemIR::TypeId assoc_const_type_id = assoc_constant_decl->type_id;
if (assoc_const_type_id.is_symbolic()) {
// Get the type of the associated constant in this interface with this
// value for `Self`.
assoc_const_type_id = GetTypeForSpecificAssociatedEntity(
context, SemIR::LocId(impl.constraint_id), impl.interface.specific_id,
decl_id, context.types().GetTypeIdForTypeInstId(impl.self_id),
witness_inst_id);
// Perform the conversion of the value to the type. We skipped this when
// forming the facet type because the type of the associated constant
// was symbolic.
auto converted_inst_id =
ConvertToValueOfType(context, SemIR::LocId(impl.constraint_id),
rewrite_inst_id, assoc_const_type_id);
// Canonicalize the converted constant value.
converted_inst_id =
context.constant_values().GetConstantInstId(converted_inst_id);
// The result of conversion can be non-constant even if the original
// value was constant.
if (converted_inst_id.has_value()) {
rewrite_inst_id = converted_inst_id;
} else {
const auto& assoc_const = context.associated_constants().Get(
assoc_constant_decl->assoc_const_id);
CARBON_DIAGNOSTIC(
AssociatedConstantNotConstantAfterConversion, Error,
"associated constant {0} given value {1} that is not constant "
"after conversion to {2}",
SemIR::NameId, InstIdAsConstant, SemIR::TypeId);
context.emitter().Emit(
impl.constraint_id, AssociatedConstantNotConstantAfterConversion,
assoc_const.name_id, rewrite_inst_id, assoc_const_type_id);
rewrite_inst_id = SemIR::ErrorInst::InstId;
}
}
CARBON_CHECK(rewrite_inst_id == context.constant_values().GetConstantInstId(
rewrite_inst_id),
"Rewritten value for associated constant is not canonical.");
table_entry = AddInst<SemIR::ImplWitnessAssociatedConstant>(
context, loc_id,
{.type_id = context.insts().Get(rewrite_inst_id).type_id(),
.inst_id = rewrite_inst_id});
}
return witness_inst_id;
}
auto ImplWitnessStartDefinition(Context& context, SemIR::Impl& impl) -> void {
CARBON_CHECK(impl.is_being_defined());
CARBON_CHECK(impl.witness_id.has_value());
if (impl.witness_id == SemIR::ErrorInst::InstId) {
return;
}
if (!RequireCompleteType(
context, context.types().GetTypeIdForTypeInstId(impl.constraint_id),
SemIR::LocId(impl.constraint_id), [&] {
CARBON_DIAGNOSTIC(ImplAsIncompleteFacetTypeDefinition, Error,
"definition of impl as incomplete facet type {0}",
InstIdAsType);
return context.emitter().Build(SemIR::LocId(impl.latest_decl_id()),
ImplAsIncompleteFacetTypeDefinition,
impl.constraint_id);
})) {
FillImplWitnessWithErrors(context, impl);
return;
}
const auto& interface = context.interfaces().Get(impl.interface.interface_id);
auto assoc_entities =
context.inst_blocks().Get(interface.associated_entities_id);
for (auto decl_id : assoc_entities) {
LoadImportRef(context, decl_id);
}
auto witness = context.insts().GetAs<SemIR::ImplWitness>(impl.witness_id);
auto witness_table =
context.insts().GetAs<SemIR::ImplWitnessTable>(witness.witness_table_id);
auto witness_block =
context.inst_blocks().GetMutable(witness_table.elements_id);
// The impl declaration may have created a placeholder witness table, or a
// full witness table. We can detect that the witness table is a placeholder
// table if it's not the `Empty` id, but it is empty still. If it was a
// placeholder, we can replace the placeholder here with a table of the proper
// size, since the interface must be complete for the impl definition.
bool witness_table_is_placeholder =
witness_table.elements_id != SemIR::InstBlockId::Empty &&
witness_block.empty();
if (witness_table_is_placeholder) {
// TODO: Since our `empty_table` repeats the same value throughout, we could
// skip an allocation here if there was a `ReplacePlaceholder` function that
// took a size and value instead of an array of values.
llvm::SmallVector<SemIR::InstId> empty_table(
assoc_entities.size(), SemIR::InstId::ImplWitnessTablePlaceholder);
context.inst_blocks().ReplacePlaceholder(witness_table.elements_id,
empty_table);
witness_block = context.inst_blocks().GetMutable(witness_table.elements_id);
}
// Check we have a value for all non-function associated constants in the
// witness.
for (auto [assoc_entity, witness_value] :
llvm::zip_equal(assoc_entities, witness_block)) {
auto decl_id = context.constant_values().GetConstantInstId(assoc_entity);
CARBON_CHECK(decl_id.has_value(), "Non-constant associated entity");
if (auto decl =
context.insts().TryGetAs<SemIR::AssociatedConstantDecl>(decl_id)) {
if (witness_value == SemIR::InstId::ImplWitnessTablePlaceholder) {
CARBON_DIAGNOSTIC(ImplAssociatedConstantNeedsValue, Error,
"associated constant {0} not given a value in impl "
"of interface {1}",
SemIR::NameId, SemIR::NameId);
CARBON_DIAGNOSTIC(AssociatedConstantHere, Note,
"associated constant declared here");
context.emitter()
.Build(impl.definition_id, ImplAssociatedConstantNeedsValue,
context.associated_constants()
.Get(decl->assoc_const_id)
.name_id,
interface.name_id)
.Note(assoc_entity, AssociatedConstantHere)
.Emit();
witness_value = SemIR::ErrorInst::InstId;
}
}
}
}
// Adds functions to the witness that the specified impl implements the given
// interface.
auto FinishImplWitness(Context& context, const SemIR::Impl& impl) -> void {
CARBON_CHECK(impl.is_being_defined());
CARBON_CHECK(impl.witness_id.has_value());
if (impl.witness_id == SemIR::ErrorInst::InstId) {
return;
}
auto witness = context.insts().GetAs<SemIR::ImplWitness>(impl.witness_id);
auto witness_table =
context.insts().GetAs<SemIR::ImplWitnessTable>(witness.witness_table_id);
auto witness_block =
context.inst_blocks().GetMutable(witness_table.elements_id);
auto& impl_scope = context.name_scopes().Get(impl.scope_id);
auto self_type_id = context.types().GetTypeIdForTypeInstId(impl.self_id);
const auto& interface = context.interfaces().Get(impl.interface.interface_id);
auto assoc_entities =
context.inst_blocks().Get(interface.associated_entities_id);
llvm::SmallVector<SemIR::InstId> used_decl_ids;
for (auto [assoc_entity, witness_value] :
llvm::zip_equal(assoc_entities, witness_block)) {
auto decl_id =
context.constant_values().GetInstId(SemIR::GetConstantValueInSpecific(
context.sem_ir(), impl.interface.specific_id, assoc_entity));
CARBON_CHECK(decl_id.has_value(), "Non-constant associated entity");
auto decl = context.insts().Get(decl_id);
CARBON_KIND_SWITCH(decl) {
case CARBON_KIND(SemIR::StructValue struct_value): {
if (struct_value.type_id == SemIR::ErrorInst::TypeId) {
witness_value = SemIR::ErrorInst::InstId;
break;
}
auto type_inst = context.types().GetAsInst(struct_value.type_id);
auto fn_type = type_inst.TryAs<SemIR::FunctionType>();
if (!fn_type) {
CARBON_FATAL("Unexpected type: {0}", type_inst);
}
auto& fn = context.functions().Get(fn_type->function_id);
auto lookup_result =
LookupNameInExactScope(context, SemIR::LocId(decl_id), fn.name_id,
impl.scope_id, impl_scope);
if (lookup_result.is_found()) {
used_decl_ids.push_back(lookup_result.target_inst_id());
witness_value = CheckAssociatedFunctionImplementation(
context, *fn_type,
context.generics().GetSelfSpecific(impl.generic_id),
lookup_result.target_inst_id(), self_type_id, impl.witness_id,
/*defer_thunk_definition=*/true);
} else {
CARBON_DIAGNOSTIC(
ImplMissingFunction, Error,
"missing implementation of {0} in impl of interface {1}",
SemIR::NameId, SemIR::NameId);
auto builder =
context.emitter().Build(impl.definition_id, ImplMissingFunction,
fn.name_id, interface.name_id);
NoteAssociatedFunction(context, builder, fn_type->function_id);
builder.Emit();
witness_value = SemIR::ErrorInst::InstId;
}
break;
}
case SemIR::AssociatedConstantDecl::Kind: {
// These are set to their final values already.
break;
}
default:
CARBON_CHECK(decl_id == SemIR::ErrorInst::InstId,
"Unexpected kind of associated entity {0}", decl);
witness_value = SemIR::ErrorInst::InstId;
break;
}
}
// TODO: Diagnose if any declarations in the impl are not in used_decl_ids.
}
auto CheckRequireDeclsSatisfied(Context& context, SemIR::LocId loc_id,
SemIR::Impl& impl) -> void {
if (impl.witness_id == SemIR::ErrorInst::InstId) {
return;
}
const auto& interface = context.interfaces().Get(impl.interface.interface_id);
if (!interface.is_complete()) {
// This will be diagnosed later. We check for required decls before starting
// the definition to avoid inserting these lookups into the definition, as
// the lookups can end up looking for the impl being defined, which creates
// a cycle.
return;
}
auto require_ids =
context.require_impls_blocks().Get(interface.require_impls_block_id);
if (require_ids.empty()) {
return;
}
// Make a facet value for the self type.
auto self_facet_value = GetConstantFacetValueForType(context, impl.self_id);
for (auto require_id : require_ids) {
const auto& require = context.require_impls().Get(require_id);
auto require_specific =
GetRequireImplsSpecificFromEnclosingSpecificWithSelfFacetValue(
context, require, impl.interface.specific_id, self_facet_value);
auto self_const_id = GetConstantValueInRequireImplsSpecific(
context, require_specific, require.self_id);
auto facet_type_const_id = GetConstantValueInRequireImplsSpecific(
context, require_specific, require.facet_type_inst_id);
auto result =
LookupImplWitness(context, loc_id, self_const_id, facet_type_const_id);
// TODO: If the facet type contains 2 interfaces, and one is not `impl`ed,
// it would be nice to diagnose which one was not `impl`ed, but that
// requires LookupImplWitness to return a partial result, or take a
// diagnostic lambda or something.
if (!result.has_value()) {
auto facet_type_inst_id =
context.constant_values().GetInstId(facet_type_const_id);
if (!result.has_error_value() &&
facet_type_inst_id != SemIR::ErrorInst::InstId) {
CARBON_DIAGNOSTIC(RequireImplsNotImplemented, Error,
"interface `{0}` being implemented requires that {1} "
"implements {2}",
SemIR::SpecificInterface, SemIR::TypeId,
SemIR::FacetTypeId);
context.emitter().Emit(
loc_id, RequireImplsNotImplemented, impl.interface,
context.types().GetTypeIdForTypeConstantId(self_const_id),
context.insts()
.GetAs<SemIR::FacetType>(facet_type_inst_id)
.facet_type_id);
}
}
if (!result.has_value() || result.has_error_value()) {
FillImplWitnessWithErrors(context, impl);
break;
}
}
}
auto FillImplWitnessWithErrors(Context& context, SemIR::Impl& impl) -> void {
if (impl.witness_id == SemIR::ErrorInst::InstId) {
return;
}
auto witness = context.insts().GetAs<SemIR::ImplWitness>(impl.witness_id);
auto witness_table =
context.insts().GetAs<SemIR::ImplWitnessTable>(witness.witness_table_id);
auto witness_block =
context.inst_blocks().GetMutable(witness_table.elements_id);
for (auto& elem : witness_block) {
if (elem == SemIR::InstId::ImplWitnessTablePlaceholder) {
elem = SemIR::ErrorInst::InstId;
}
}
impl.witness_id = SemIR::ErrorInst::InstId;
}
auto IsImplEffectivelyFinal(Context& context, const SemIR::Impl& impl) -> bool {
return impl.is_final ||
(context.constant_values().Get(impl.self_id).is_concrete() &&
context.constant_values().Get(impl.constraint_id).is_concrete());
}
auto CheckConstraintIsInterface(Context& context, SemIR::InstId impl_decl_id,
SemIR::InstId self_id,
SemIR::TypeInstId constraint_id)
-> SemIR::SpecificInterface {
auto facet_type_id = context.types().GetTypeIdForTypeInstId(constraint_id);
if (facet_type_id == SemIR::ErrorInst::TypeId) {
return SemIR::SpecificInterface::None;
}
auto facet_type = context.types().TryGetAs<SemIR::FacetType>(facet_type_id);
if (!facet_type) {
CARBON_DIAGNOSTIC(ImplAsNonFacetType, Error, "impl as non-facet type {0}",
InstIdAsType);
context.emitter().Emit(impl_decl_id, ImplAsNonFacetType, constraint_id);
return SemIR::SpecificInterface::None;
}
auto identified_id = RequireIdentifiedFacetType(
context, SemIR::LocId(constraint_id),
context.constant_values().Get(self_id), *facet_type, [&] {
CARBON_DIAGNOSTIC(ImplOfUnidentifiedFacetType, Error,
"facet type {0} cannot be identified in `impl as`",
InstIdAsType);
return context.emitter().Build(
impl_decl_id, ImplOfUnidentifiedFacetType, constraint_id);
});
if (!identified_id.has_value()) {
return SemIR::SpecificInterface::None;
}
const auto& identified = context.identified_facet_types().Get(identified_id);
if (!identified.is_valid_impl_as_target()) {
CARBON_DIAGNOSTIC(ImplOfNotOneInterface, Error,
"impl as {0} interfaces, expected 1", int);
context.emitter().Emit(impl_decl_id, ImplOfNotOneInterface,
identified.num_interfaces_to_impl());
return SemIR::SpecificInterface::None;
}
return identified.impl_as_target_interface();
}
} // namespace Carbon::Check
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