feat: trait 接口系统 — trait Show { fn method } + extend Trait Struct { }

src/ast/ast.h

@@ -32,6 +32,7 @@ typedef enum {
     AST_METHOD_CALL,      // receiver.method(args)
     AST_MOD_DECL,         // mod foo;
     AST_USE_DECL,         // use foo::bar;
+    AST_TRAIT_DECL,       // trait Name { fn ... }
 } AstKind;
 
 typedef enum {
@@ -127,6 +128,8 @@ struct AstNode {
         struct { const char* name; struct AstNode* ast; } mod_decl;
         // AST_USE_DECL
         struct { const char* path; const char* item; } use_decl;
+        // AST_TRAIT_DECL
+        struct { const char* name; struct AstNode** methods; size_t method_count; } trait_decl;
     } as;
 };
 
@@ -175,5 +178,6 @@ AstNode* ast_make_impl_block(void* alloc, const char* struct_name, AstNode** met
 AstNode* ast_make_method_call(void* alloc, AstNode* receiver, const char* method, AstNode** args, const char** arg_names, size_t count, SourceLoc loc);
 AstNode* ast_make_mod_decl(void* alloc, const char* name, AstNode* sub_ast, SourceLoc loc);
 AstNode* ast_make_use_decl(void* alloc, const char* path, const char* item, SourceLoc loc);
+AstNode* ast_make_trait_decl(void* alloc, const char* name, AstNode** methods, size_t count, SourceLoc loc);
 
 #endif