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Fix crash from accessing a Check::Context during lowering (#7335)

Browse Source 
In generate_ast.cpp, an `CarbonExternalASTSource` is installed that has
a `Check::Context` pointer. During lowering, this `ExternalASTSource` is
still installed, and using it can cause a crash if the now-invalid
pointer is dereferenced.

Fix by adding a new `ReadOnlyASTSource` in sem_ir, and using that during
lowering.

`CarbonExternalASTSource` now inherits from `ReadOnlyASTSource` to avoid
some code duplication.

In generate_ast.cpp, we now always install a multiplex source, even if
there's only one child source. Clang internally keeps pointers to the
top-level `ExternalASTSource` installed via `setExternalSource`, and
those pointers aren't updated if `setExternalSource` is called again. By
using `MultiplexExternalSemaSource`, we can keep the top-level
`ExternalASTSource` pointer the same, and only update its children.

Using `MultiplexExternalSemaSource` this way requires a new constructor
and a method to modify its child sources; added a new LLVM patch adding
those.

https://github.com/carbon-language/carbon-lang/issues/7142
This commit is contained in:
Nicholas Bishop
2026-06-12 18:05:19 +00:00
committed by GitHub
parent f3b8e231ca
commit afd679129d
14 changed files with 495 additions and 169 deletions
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toolchain/check/cpp/export.cpp
+4 -72
View File
@@ -177,39 +177,6 @@ auto ExportClassToCpp(Context& context, SemIR::LocId loc_id,
return record_decl;
}
// Get the `StructTypeField`s from a class's object repr.
static auto GetStructTypeFields(Context& context,
const SemIR::Class& class_info)
-> llvm::ArrayRef<SemIR::StructTypeField> {
if (class_info.adapt_id.has_value()) {
// The representation of an adapter won't necessarily be a
// struct. Return an empty array since adapters can't declare
// fields.
return {};
}
auto object_repr_type_id =
class_info.GetObjectRepr(context.sem_ir(), SemIR::SpecificId::None);
if (object_repr_type_id == SemIR::ErrorInst::TypeId) {
return {};
}
auto struct_type =
context.types().GetAs<SemIR::StructType>(object_repr_type_id);
return context.struct_type_fields().Get(struct_type.fields_id);
}
static auto LookupClassFieldByStructField(
const Context& context, const SemIR::NameScope& class_scope,
const SemIR::StructTypeField& struct_field)
-> std::optional<SemIR::InstStore::GetAsWithIdResult<SemIR::FieldDecl>> {
if (auto entry_id = class_scope.Lookup(struct_field.name_id)) {
auto field_inst_id =
class_scope.GetEntry(*entry_id).result.target_inst_id();
return context.insts().TryGetAsWithId<SemIR::FieldDecl>(field_inst_id);
}
return std::nullopt;
}
static auto SetCppClassMemberAccess(const SemIR::NameScope& class_scope,
SemIR::NameId member_name_id,
clang::Decl* member) -> void {
@@ -265,9 +232,10 @@ auto ExportAllFieldsToCpp(Context& context, SemIR::Class& class_info) -> void {
const auto& class_scope = context.name_scopes().Get(class_info.scope_id);
for (const auto& struct_field : GetStructTypeFields(context, class_info)) {
auto class_field =
LookupClassFieldByStructField(context, class_scope, struct_field);
for (const auto& struct_field :
class_info.GetStructTypeFields(context.sem_ir())) {
auto class_field = LookupClassFieldByStructField(context.sem_ir(),
class_scope, struct_field);
if (!class_field) {
continue;
}
@@ -314,42 +282,6 @@ auto ExportFieldToCpp(Context& context, SemIR::InstId field_inst_id,
return nullptr;
}
auto CalculateCppFieldOffsets(
Context& context, SemIR::ClassId class_id,
llvm::DenseMap<const clang::FieldDecl*, uint64_t>& field_offsets) -> bool {
auto class_info = context.classes().Get(class_id);
const auto& class_scope = context.name_scopes().Get(class_info.scope_id);
auto class_layout = SemIR::ObjectLayout::Empty();
for (const auto& struct_field : GetStructTypeFields(context, class_info)) {
auto field_type_id = context.sem_ir().types().GetTypeIdForTypeInstId(
struct_field.type_inst_id);
auto field_layout = context.sem_ir()
.types()
.GetCompleteTypeInfo(field_type_id)
.object_layout;
// Use the field's name to look up the corresponding entry in the
// class. If it's a `FieldDecl`, write out the offset of the
// corresponding `clang::FieldDecl`.
auto class_field =
LookupClassFieldByStructField(context, class_scope, struct_field);
if (class_field) {
auto* cpp_field_decl =
ExportFieldToCpp(context, class_field->inst_id, class_field->inst);
if (!cpp_field_decl) {
return false;
}
field_offsets.insert(
{cpp_field_decl, class_layout.FieldOffset(field_layout).bits()});
}
class_layout.AppendField(field_layout);
}
return true;
}
namespace {
struct FunctionInfo {
struct Param {