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Support assigning to a variable through an imported macro (#6827)

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Support assigning to a variable through an imported macro

Example:

```carbon
import Cpp inline '''
int v = 1;
#define m v
''';

fn F() {
  Cpp.m = 2;
}
```
This commit is contained in:
Nicholas Bishop
2026-03-05 18:24:32 +00:00
committed by GitHub
parent 002b7c74ea
commit e5957037fb
4 changed files with 223 additions and 47 deletions
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toolchain/check/cpp/macros.cpp
+31 -20
View File
@@ -44,9 +44,9 @@ static auto MapConstant(Context& context, SemIR::LocId loc_id,
return SemIR::ErrorInst::InstId;
}
auto TryEvaluateMacroToConstant(Context& context, SemIR::LocId loc_id,
SemIR::NameId name_id,
clang::MacroInfo* macro_info) -> SemIR::InstId {
auto TryEvaluateMacro(Context& context, SemIR::LocId loc_id,
SemIR::NameId name_id, clang::MacroInfo* macro_info)
-> SemIR::InstId {
auto name_str_opt = context.names().GetAsStringIfIdentifier(name_id);
CARBON_CHECK(macro_info, "macro info missing");
@@ -102,30 +102,41 @@ auto TryEvaluateMacroToConstant(Context& context, SemIR::LocId loc_id,
}
clang::Expr::EvalResult evaluated_result;
CARBON_CHECK(result_expr->EvaluateAsConstantExpr(evaluated_result,
sema.getASTContext()));
if (!result_expr->EvaluateAsConstantExpr(evaluated_result,
sema.getASTContext())) {
CARBON_FATAL("failed to evaluate macro as constant expression");
}
clang::APValue ap_value = evaluated_result.Val;
// TODO: Add support for other types.
if (ap_value.isLValue()) {
if (!result_expr->EvaluateAsInt(evaluated_result, sema.getASTContext())) {
context.TODO(loc_id,
"Unsupported: macro evaluated to a non-integer LValue");
if (result_expr->isGLValue()) {
const auto* value_decl =
ap_value.getLValueBase().get<const clang::ValueDecl*>();
auto key = SemIR::ClangDeclKey::ForNonFunctionDecl(
// TODO: can this const_cast be avoided?
const_cast<clang::ValueDecl*>(value_decl));
if (ap_value.hasLValuePath() && ap_value.getLValuePath().size() > 0) {
context.TODO(loc_id, "Macro evaluated to an lvalue with a path: " +
ap_value.getAsString(context.ast_context(),
result_expr->getType()));
return SemIR::ErrorInst::InstId;
}
ap_value = evaluated_result.Val;
}
auto const_id =
MapAPValueToConstant(context, loc_id, ap_value, result_expr->getType());
if (const_id == SemIR::ConstantId::NotConstant) {
context.TODO(loc_id,
"Unsupported: macro evaluated to a constant of type: " +
result_expr->getType().getAsString());
return SemIR::ErrorInst::InstId;
}
return ImportCppDecl(context, loc_id, key);
} else {
auto const_id =
MapAPValueToConstant(context, loc_id, ap_value, result_expr->getType());
if (const_id == SemIR::ConstantId::NotConstant) {
context.TODO(loc_id,
"Unsupported: macro evaluated to a constant of type: " +
result_expr->getType().getAsString());
return SemIR::ErrorInst::InstId;
}
return context.constant_values().GetInstId(const_id);
return context.constant_values().GetInstId(const_id);
}
}
} // namespace Carbon::Check