feat(codegen): return C-struct records by value

EXTERN_FUNCTION may now return a C-struct record by value, either through
caller-supplied sret memory or as a coerced value stored back into the
record, as clang arranges it. This removes the last by-value rejection.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 5 insertions, 10 deletions

diff --git a/lib/CodeGen/FunctionGen.cc b/lib/CodeGen/FunctionGen.cc
index 9cc1c08..b79698e 100644
--- a/lib/CodeGen/FunctionGen.cc
+++ b/lib/CodeGen/FunctionGen.cc
@@ -291,9 +291,9 @@ bool FunctionGen::emitExternPrototype(PrototypeAST *Proto) {
         return false;
     }
 
-    // Records cross the C boundary only as C structs, and are not yet
-    // returned by value. What names the parameter or return type in diagnostics.
-    auto CheckRecord = [&](const TypeInfo *Info, const std::string &What, bool IsResult) {
+    // Records cross the C boundary only as C structs, by value or through a
+    // pointer type. What names the parameter or return type in diagnostics.
+    auto CheckRecord = [&](const TypeInfo *Info, const std::string &What) {
         const TypeInfo *Record = Info->Kind == TypeKind::Pointer
             ? Types.resolve(Info->Pointer.PointeeTypeName) : Info;
         if (!Record || !Record->isRecord() || Record->IsClass) return true;
@@ -303,11 +303,6 @@ bool FunctionGen::emitExternPrototype(PrototypeAST *Proto) {
                         Record->Name.c_str(), Why.c_str());
             return false;
         }
-        if (IsResult && Record == Info) {
-            reportError("%s cannot be record %s by value; use a pointer type to it", What.c_str(),
-                        Record->Name.c_str());
-            return false;
-        }
         return true;
     };
 
@@ -328,7 +323,7 @@ bool FunctionGen::emitExternPrototype(PrototypeAST *Proto) {
             reportError("Unknown type %s", P.TypeName.c_str());
             return false;
         }
-        if (!CheckRecord(Info, "EXTERN parameter " + std::to_string(I + 1) + " of " + Name, false))
+        if (!CheckRecord(Info, "EXTERN parameter " + std::to_string(I + 1) + " of " + Name))
             return false;
         if (!Types.isExternType(Info)) {
             reportError("EXTERN parameter %zu of %s must be a non-void C type (got %s)",
@@ -347,7 +342,7 @@ bool FunctionGen::emitExternPrototype(PrototypeAST *Proto) {
             reportError("Unknown type %s", Proto->getReturnType().c_str());
             return false;
         }
-        if (!CheckRecord(Info, "The return type of EXTERN_FUNCTION " + Name, true)) return false;
+        if (!CheckRecord(Info, "The return type of EXTERN_FUNCTION " + Name)) return false;
         if (!Types.isExternType(Info)) {
             reportError("EXTERN_FUNCTION %s must return a non-void C type (got %s)",
                         Name.c_str(), Proto->getReturnType().c_str());