Compiler didn't check foreach over flexible array member, and folding a flexible array member was allowed #2164.

releasenotes.md

@@ -52,6 +52,7 @@
 - `$$sat_mul` was missing.
 - `for` with incorrect `var` declaration caused crash #2154.
 - Check pointer/slice/etc on `[out]` and `&` params. #2156.
+- Compiler didn't check foreach over flexible array member, and folding a flexible array member was allowed #2164.
 
 ### Stdlib changes
 - Added `String.quick_ztr` and `String.is_zstr`

src/compiler/sema_decls.c

@@ -2374,7 +2374,7 @@ static inline bool unit_add_method(SemaContext *context, Type *parent_type, Decl
 	other = sema_resolve_method(unit, parent, name, &ambiguous, &private);
 	if (other)
 	{
-		if (unit->module->generic_module && other->unit->module->generic_module == unit->module->generic_module)
+		if (unit->module->generic_module && other->unit->module->generic_module == unit->module->generic_module && other->unit->module != unit->module)
 		{
 			const char *module_name = unit->module->generic_module->name->module;
 			RETURN_SEMA_ERROR(method, "The same method is generated by multiple instances of '%s': '%s%s' and '%s%s'. "

src/compiler/sema_expr.c

@@ -4981,6 +4981,7 @@ EVAL:
 	switch (result->kind)
 	{
 		case CONST_INIT_ZERO:
+			if (member->type->type_kind == TYPE_FLEXIBLE_ARRAY) return false;
 			expr_rewrite_to_const_zero(expr, member->type);
 			break;
 		case CONST_INIT_STRUCT:
@@ -5688,6 +5689,10 @@ CHECK_DEEPER:
 		{
 			if (!sema_expr_fold_to_member(expr, current_parent, member))
 			{
+				if (member->type->type_kind == TYPE_FLEXIBLE_ARRAY)
+				{
+					RETURN_SEMA_ERROR(expr, "Could not fold to member '%s', it's a flexible array member which is always empty.", member->name);
+				}
 				RETURN_SEMA_ERROR(expr, "Could not fold to member '%s' – it wasn't the last assigned member.", member->name);
 			}
 			return true;

src/compiler/sema_stmts.c

@@ -1497,6 +1497,10 @@ static inline bool sema_analyse_foreach_stmt(SemaContext *context, Ast *statemen
 	// At this point we should have dereferenced any pointer or bailed.
 	ASSERT_SPAN(enumerator, !type_is_pointer(enumerator->type));
 
+	if (enumerator->type->type_kind == TYPE_FLEXIBLE_ARRAY)
+	{
+		RETURN_SEMA_ERROR(enumerator, "It is not possible to enumerate over a flexible array member.", type_quoted_error_string(enumerator->type));
+	}
 	// Check that we can even index this expression, this will dig into the flattened type.
 	Type *value_type = type_get_indexed_type(enumerator->type);
 

test/test_suite/generic/generic_self_ref.c3

@@ -10,7 +10,7 @@ struct Widget
 	List {any} children;
 }
 
-fn void Widget{Label}.draw(Widget* self) // #error: This identifier is recursively using gui::widget
+fn void Widget{Label}.draw(Widget* self) // #error: The same method is generated by multiple instances
 {
 	io::printfn("Hello Label");
 }

test/test_suite/statements/foreach_fails.c3

@@ -0,0 +1,15 @@
+struct Abc
+{
+  int a;
+  int[*] b;
+}
+fn void test()
+{
+	Abc y = {};
+	foreach (x : y.b) {} // #error: It is not possible to enumerate over a flexible
+}
+fn int main()
+{
+  foreach (x : (Abc){}.b) {} // #error: it's a flexible array member
+  return 0;
+}