feat: struct参数/返回值 + SourceLoc + 测试补全

- struct 可作函数参数和返回值 (fn make_point -> Point)
- SourceLoc 抽象: 所有 ast_make_* 参数 + AstNode 迁移完毕
- sema: +4 struct 类型检查测试 (字段类型/未定义/数量/嵌套)
- codegen: +2 struct IR 生成测试 (decl + field_access)
- 新增集成测试 14_struct_fn.l

测试: 104 单元 + 14 集成 = 全部通过

test/test_sema.c

@@ -115,6 +115,76 @@ void test_str_concat_type_ok() {
     arena_destroy(&a);
 }
 
+/* === struct 类型检查测试 === */
+
+void test_struct_field_type_mismatch() {
+    Arena a = arena_create(1);
+    size_t tc; ErrorInfo lex_err = {0};
+    Token* toks = lex(&a,
+        "struct Point { x: i64, y: i64 } fn main() { let p: Point = Point { x: 10, y: true }; return; }",
+        "test", &tc, &lex_err);
+    ASSERT(toks != NULL);
+    ErrorInfo parse_err = {0};
+    AstNode* ast = parse(&a, toks, tc, "test", &parse_err);
+    ASSERT(ast != NULL);
+
+    ErrorList errors; error_init(&errors);
+    sema_analyze(ast, &errors, &a);
+    ASSERT(errors.count > 0);  // y 字段类型不匹配: true 是 bool, 不是 i64
+    arena_destroy(&a);
+}
+
+void test_struct_undefined() {
+    Arena a = arena_create(1);
+    size_t tc; ErrorInfo lex_err = {0};
+    Token* toks = lex(&a,
+        "fn main() { let p: Unknown = Unknown { x: 1 }; return; }",
+        "test", &tc, &lex_err);
+    ASSERT(toks != NULL);
+    ErrorInfo parse_err = {0};
+    AstNode* ast = parse(&a, toks, tc, "test", &parse_err);
+    ASSERT(ast != NULL);
+
+    ErrorList errors; error_init(&errors);
+    sema_analyze(ast, &errors, &a);
+    ASSERT(errors.count > 0);  // Unknown 未定义
+    arena_destroy(&a);
+}
+
+void test_struct_field_count_mismatch() {
+    Arena a = arena_create(1);
+    size_t tc; ErrorInfo lex_err = {0};
+    Token* toks = lex(&a,
+        "struct Point { x: i64, y: i64 } fn main() { let p: Point = Point { x: 10 }; return; }",
+        "test", &tc, &lex_err);
+    ASSERT(toks != NULL);
+    ErrorInfo parse_err = {0};
+    AstNode* ast = parse(&a, toks, tc, "test", &parse_err);
+    ASSERT(ast != NULL);
+
+    ErrorList errors; error_init(&errors);
+    sema_analyze(ast, &errors, &a);
+    ASSERT(errors.count > 0);  // 缺少字段 'y'
+    arena_destroy(&a);
+}
+
+void test_struct_nested_type_ok() {
+    Arena a = arena_create(1);
+    size_t tc; ErrorInfo lex_err = {0};
+    Token* toks = lex(&a,
+        "struct Point { x: i64, y: i64 } struct Rect { tl: Point, br: Point } fn main() { let r: Rect = Rect { tl: Point { x: 0, y: 0 }, br: Point { x: 1, y: 1 } }; print_i64(r.tl.x); return; }",
+        "test", &tc, &lex_err);
+    ASSERT(toks != NULL);
+    ErrorInfo parse_err = {0};
+    AstNode* ast = parse(&a, toks, tc, "test", &parse_err);
+    ASSERT(ast != NULL);
+
+    ErrorList errors; error_init(&errors);
+    sema_analyze(ast, &errors, &a);
+    ASSERT(errors.count == 0);  // 嵌套结构体类型检查应通过
+    arena_destroy(&a);
+}
+
 int main(void) {
     TEST_RUN(test_type_error);
     TEST_RUN(test_undefined_var);
@@ -123,5 +193,9 @@ int main(void) {
     TEST_RUN(test_assign_immutable_error);
     TEST_RUN(test_str_type_ok);
     TEST_RUN(test_str_concat_type_ok);
+    TEST_RUN(test_struct_field_type_mismatch);
+    TEST_RUN(test_struct_undefined);
+    TEST_RUN(test_struct_field_count_mismatch);
+    TEST_RUN(test_struct_nested_type_ok);
     return test_summary();
 }