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Support for importing C++ base classes. (#5856)

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For now, provide no support for virtual base classes and only minimal
support for multiple inheritance.
This commit is contained in:
Richard Smith
2025-07-28 20:56:06 +00:00
committed by GitHub
parent 0d74162e2a
commit 5de47962b0
5 changed files with 1174 additions and 336 deletions
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toolchain/check/import_cpp.cpp
+54 -6
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@@ -507,7 +507,7 @@ static auto BuildClassDecl(Context& context,
// returns a corresponding complete type witness instruction.
// TODO: Remove recursion into mapping field types.
// NOLINTNEXTLINE(misc-no-recursion)
static auto ImportClassObjectRepr(Context& context,
static auto ImportClassObjectRepr(Context& context, SemIR::ClassId class_id,
SemIR::ImportIRInstId import_ir_inst_id,
SemIR::TypeInstId class_type_inst_id,
const clang::CXXRecordDecl* clang_def)
@@ -516,7 +516,7 @@ static auto ImportClassObjectRepr(Context& context,
// representation. This allows our tests to continue to pass while we don't
// properly support initializing imported C++ classes.
// TODO: Remove this.
if (clang_def->isEmpty()) {
if (clang_def->isEmpty() && !clang_def->getNumBases()) {
return context.types().GetAsTypeInstId(AddInst(
context,
MakeImportedLocIdAndInst(
@@ -540,7 +540,55 @@ static auto ImportClassObjectRepr(Context& context,
static_assert(SemIR::CustomLayoutId::FirstFieldIndex == 2);
// TODO: Import vptr(s).
// TODO: Import bases.
// Import bases.
for (const auto& base : clang_def->bases()) {
if (base.isVirtual()) {
// TODO: Handle virtual bases. We don't actually know where they go in the
// layout. We may also want to use a different size in the layout for
// `partial C`, excluding the virtual base. It's also not entirely safe to
// just skip over the virtual base, as the type we would construct would
// have a misleading size.
context.TODO(import_ir_inst_id, "class with virtual bases");
return SemIR::ErrorInst::TypeInstId;
}
auto [base_type_inst_id, base_type_id] =
MapType(context, import_ir_inst_id, base.getType());
if (!base_type_id.has_value()) {
// TODO: If the base class's type can't be mapped, skip it.
continue;
}
auto base_decl_id = AddInst(
context,
MakeImportedLocIdAndInst(
context, import_ir_inst_id,
SemIR::BaseDecl{.type_id = GetUnboundElementType(
context, class_type_inst_id, base_type_inst_id),
.base_type_inst_id = base_type_inst_id,
.index = SemIR::ElementIndex(fields.size())}));
// If there's exactly one base class, treat it as a Carbon base class too.
// TODO: Improve handling for the case where the class has multiple base
// classes.
if (clang_def->getNumBases() == 1) {
auto& class_info = context.classes().Get(class_id);
CARBON_CHECK(!class_info.base_id.has_value());
class_info.base_id = base_decl_id;
}
auto* base_class = base.getType()->getAsCXXRecordDecl();
CARBON_CHECK(base_class, "Base class {0} is not a class",
base.getType().getAsString());
auto base_offset = base.isVirtual()
? clang_layout.getVBaseClassOffset(base_class)
: clang_layout.getBaseClassOffset(base_class);
layout.push_back(base_offset.getQuantity());
fields.push_back(
{.name_id = SemIR::NameId::Base, .type_inst_id = base_type_inst_id});
}
// Import fields.
for (auto* decl : clang_def->decls()) {
@@ -644,8 +692,8 @@ static auto BuildClassDefinition(Context& context,
context.inst_block_stack().Push();
// Compute the class's object representation.
auto object_repr_id = ImportClassObjectRepr(context, import_ir_inst_id,
class_inst_id, clang_def);
auto object_repr_id = ImportClassObjectRepr(
context, class_id, import_ir_inst_id, class_inst_id, clang_def);
class_info.complete_type_witness_id = AddInst<SemIR::CompleteTypeWitness>(
context, import_ir_inst_id,
{.type_id = GetSingletonType(context, SemIR::WitnessType::TypeInstId),
@@ -1195,7 +1243,7 @@ static auto GetDependentUnimportedTypeDecls(const Context& context,
if (!IsClangDeclImported(context, record_decl)) {
return {record_decl};
}
// TODO: Also collect field types.
// TODO: Also collect base and field types.
}
}