Prevent multiple uses of the same Objective-C class name

src/check_builtin.cpp

@@ -223,9 +223,9 @@ gb_internal void add_objc_proc_type(CheckerContext *c, Ast *call, Type *return_t
 	data.kind = kind;
 	data.proc_type = alloc_type_proc(scope, params, param_types.count, results, results->Tuple.variables.count, false, ProcCC_CDecl);
 
-	mutex_lock(&c->info->objc_types_mutex);
+	mutex_lock(&c->info->objc_objc_msgSend_mutex);
 	map_set(&c->info->objc_msgSend_types, call, data);
-	mutex_unlock(&c->info->objc_types_mutex);
+	mutex_unlock(&c->info->objc_objc_msgSend_mutex);
 
 	try_to_add_package_dependency(c, "runtime", "objc_msgSend");
 	try_to_add_package_dependency(c, "runtime", "objc_msgSend_fpret");

src/check_decl.cpp

@@ -524,7 +524,16 @@ gb_internal void check_type_decl(CheckerContext *ctx, Entity *e, Ast *init_expr,
 	if (decl != nullptr) {
 		AttributeContext ac = {};
 		check_decl_attributes(ctx, decl->attributes, type_decl_attribute, &ac);
+
 		if (e->kind == Entity_TypeName && ac.objc_class != "") {
+
+			mutex_lock(&ctx->info->objc_class_name_mutex);
+			bool class_exists = string_set_update(&ctx->info->obcj_class_name_set, ac.objc_class);
+			mutex_unlock(&ctx->info->objc_class_name_mutex);
+			if (class_exists) {
+				error(e->token, "@(objc_class) '%s' has already been used elsewhere", ac.objc_class);
+			}
+
 			e->TypeName.objc_class_name = ac.objc_class;
 
 			if (ac.objc_is_implementation) {

src/checker.cpp

@@ -1390,6 +1390,7 @@ gb_internal void init_checker_info(CheckerInfo *i) {
 
 	map_init(&i->objc_msgSend_types);
 	mpsc_init(&i->objc_class_implementations, a);
+	string_set_init(&i->obcj_class_name_set, 0);
 	map_init(&i->objc_method_implementations);
 
 	string_map_init(&i->load_file_cache);

src/checker.hpp

@@ -487,9 +487,11 @@ struct CheckerInfo {
 
 	MPSCQueue<Ast *> intrinsics_entry_point_usage;
 
-	BlockingMutex objc_types_mutex;
+	BlockingMutex objc_objc_msgSend_mutex;
 	PtrMap<Ast *, ObjcMsgData> objc_msgSend_types;
 
+	BlockingMutex objc_class_name_mutex;
+	StringSet obcj_class_name_set;
 	MPSCQueue<Entity *> objc_class_implementations;
 
 	BlockingMutex objc_method_mutex;