test: sema + codegen 测试补全 — 86 单元测试

- test_sema: +4 测试 (let_mut_assign_ok, assign_immutable_error, str_type_ok, str_concat_ok) → 21 tests
- test_codegen: +1 测试 (while_loop LLVMVerifyModule) → 9 tests
- 总单元测试: 86 (词法41+语法15+语义21+代码生成9)
- 基于 Codex 分析报告 §5-3 §5-4 技术债务补偿

test/test_sema.c

@@ -51,9 +51,77 @@ void test_simple_ok() {
     arena_destroy(&a);
 }
 
+void test_let_mut_assign_ok() {
+    Arena a = arena_create(1);
+    size_t tc; ErrorInfo lex_err = {0};
+    Token* toks = lex(&a,
+        "fn main() { let mut x: i64 = 0; x = 42; print_i64(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);
+    arena_destroy(&a);
+}
+
+void test_assign_immutable_error() {
+    Arena a = arena_create(1);
+    size_t tc; ErrorInfo lex_err = {0};
+    Token* toks = lex(&a,
+        "fn main() { let x: i64 = 0; x = 42; 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);  // 不可变变量赋值应报错
+    arena_destroy(&a);
+}
+
+void test_str_type_ok() {
+    Arena a = arena_create(1);
+    size_t tc; ErrorInfo lex_err = {0};
+    Token* toks = lex(&a,
+        "fn main() { let msg: str = \"hello\"; print_str(msg); 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);
+    arena_destroy(&a);
+}
+
+void test_str_concat_type_ok() {
+    Arena a = arena_create(1);
+    size_t tc; ErrorInfo lex_err = {0};
+    Token* toks = lex(&a,
+        "fn main() { let a: str = \"a\"; let b: str = \"b\"; let c: str = a + b; print_str(c); 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);
+    arena_destroy(&a);
+}
+
 int main(void) {
     TEST_RUN(test_type_error);
     TEST_RUN(test_undefined_var);
     TEST_RUN(test_simple_ok);
+    TEST_RUN(test_let_mut_assign_ok);
+    TEST_RUN(test_assign_immutable_error);
+    TEST_RUN(test_str_type_ok);
+    TEST_RUN(test_str_concat_type_ok);
     return test_summary();
 }