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

src/ast/ast.h

@@ -42,8 +42,7 @@ typedef struct {
 struct AstNode {
     AstKind   kind;
     TypeInfo  type;         // 语义分析后填充，默认为 TYPE_UNKNOWN
-    int       line;         // 源文件行号
-    int       col;          // 源文件列号
+    SourceLoc loc;          // 源码位置
 
     // 节点特有数据（按 kind 解释）
     union {
@@ -52,7 +51,8 @@ struct AstNode {
                  struct AstNode** structs;   size_t struct_count; } program;
         // AST_FUNCTION
         struct { const char* name; struct AstNode** params; size_t param_count;
-                 TypeKind return_type; struct AstNode* body; } function;
+                 TypeKind return_type; const char* return_struct_type_name;
+                 struct AstNode* body; } function;
         // AST_PARAMETER (也用作结构体字段: name + type)
         struct { const char* name; TypeKind type; const char* struct_type_name; } parameter;
         // AST_BLOCK
@@ -92,28 +92,28 @@ struct AstNode {
 
 // 创建节点的辅助函数（内存来自 arena，通过 void* 传递避免循环依赖）
 AstNode* ast_make_program(void* alloc, AstNode** fns, size_t fn_count,
-                          AstNode** structs, size_t struct_count, int line, int col);
+                          AstNode** structs, size_t struct_count, SourceLoc loc);
 AstNode* ast_make_function(void* alloc, const char* name, AstNode** params, size_t pcount,
-                           TypeKind ret, AstNode* body, int line, int col);
-AstNode* ast_make_parameter(void* alloc, const char* name, TypeKind type, const char* struct_type_name, int line, int col);
-AstNode* ast_make_block(void* alloc, AstNode** stmts, size_t count, int line, int col);
+                           TypeKind ret, const char* ret_struct_name, AstNode* body, SourceLoc loc);
+AstNode* ast_make_parameter(void* alloc, const char* name, TypeKind type, const char* struct_type_name, SourceLoc loc);
+AstNode* ast_make_block(void* alloc, AstNode** stmts, size_t count, SourceLoc loc);
 AstNode* ast_make_let(void* alloc, const char* name, TypeKind annot_type, bool has_type_annot,
-                      bool is_mut, AstNode* init, const char* struct_type_name, int line, int col);
-AstNode* ast_make_assign(void* alloc, const char* name, AstNode* value, int line, int col);
-AstNode* ast_make_if(void* alloc, AstNode* cond, AstNode* then_b, AstNode* else_b, int line, int col);
-AstNode* ast_make_while(void* alloc, AstNode* cond, AstNode* body, int line, int col);
-AstNode* ast_make_return(void* alloc, AstNode* expr, int line, int col);
-AstNode* ast_make_expr_stmt(void* alloc, AstNode* expr, int line, int col);
-AstNode* ast_make_binary(void* alloc, BinaryOp op, AstNode* left, AstNode* right, int line, int col);
-AstNode* ast_make_unary(void* alloc, BinaryOp op, AstNode* operand, int line, int col);
-AstNode* ast_make_call(void* alloc, const char* name, AstNode** args, size_t count, int line, int col);
-AstNode* ast_make_literal_i64(void* alloc, int64_t val, int line, int col);
-AstNode* ast_make_literal_f64(void* alloc, double val, int line, int col);
-AstNode* ast_make_literal_bool(void* alloc, bool val, int line, int col);
-AstNode* ast_make_literal_str(void* alloc, const char* val, int line, int col);
-AstNode* ast_make_ident(void* alloc, const char* name, int line, int col);
-AstNode* ast_make_struct_decl(void* alloc, const char* name, AstNode** fields, size_t count, int line, int col);
-AstNode* ast_make_struct_init(void* alloc, const char* type_name, const char** fnames, AstNode** fvals, size_t count, int line, int col);
-AstNode* ast_make_field_access(void* alloc, AstNode* object, const char* field, int line, int col);
+                      bool is_mut, AstNode* init, const char* struct_type_name, SourceLoc loc);
+AstNode* ast_make_assign(void* alloc, const char* name, AstNode* value, SourceLoc loc);
+AstNode* ast_make_if(void* alloc, AstNode* cond, AstNode* then_b, AstNode* else_b, SourceLoc loc);
+AstNode* ast_make_while(void* alloc, AstNode* cond, AstNode* body, SourceLoc loc);
+AstNode* ast_make_return(void* alloc, AstNode* expr, SourceLoc loc);
+AstNode* ast_make_expr_stmt(void* alloc, AstNode* expr, SourceLoc loc);
+AstNode* ast_make_binary(void* alloc, BinaryOp op, AstNode* left, AstNode* right, SourceLoc loc);
+AstNode* ast_make_unary(void* alloc, BinaryOp op, AstNode* operand, SourceLoc loc);
+AstNode* ast_make_call(void* alloc, const char* name, AstNode** args, size_t count, SourceLoc loc);
+AstNode* ast_make_literal_i64(void* alloc, int64_t val, SourceLoc loc);
+AstNode* ast_make_literal_f64(void* alloc, double val, SourceLoc loc);
+AstNode* ast_make_literal_bool(void* alloc, bool val, SourceLoc loc);
+AstNode* ast_make_literal_str(void* alloc, const char* val, SourceLoc loc);
+AstNode* ast_make_ident(void* alloc, const char* name, SourceLoc loc);
+AstNode* ast_make_struct_decl(void* alloc, const char* name, AstNode** fields, size_t count, SourceLoc loc);
+AstNode* ast_make_struct_init(void* alloc, const char* type_name, const char** fnames, AstNode** fvals, size_t count, SourceLoc loc);
+AstNode* ast_make_field_access(void* alloc, AstNode* object, const char* field, SourceLoc loc);
 
 #endif