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

src/ast/ast.c

@@ -274,3 +274,11 @@ AstNode* ast_make_use_decl(void* alloc, const char* path, const char* item, Sour
     n->as.use_decl.item = item;
     return n;
 }
+
+AstNode* ast_make_trait_decl(void* alloc, const char* name, AstNode** methods, size_t count, SourceLoc loc) {
+    NEW(alloc, AST_TRAIT_DECL);
+    n->as.trait_decl.name = name;
+    n->as.trait_decl.methods = methods;
+    n->as.trait_decl.method_count = count;
+    return n;
+}

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

src/codegen/codegen.c

@@ -431,6 +431,10 @@ static LLVMValueRef codegen_expr(CgCtx* ctx, AstNode* node) {
     case AST_METHOD_CALL: {
         const char* struct_name = node->as.method_call.receiver->type.struct_name;
         char mangled[256];
+        // 若 method_name 已含 $（trait 方法，sema 已设置全限定名），直接用
+        if (strchr(node->as.method_call.method_name, '$'))
+            snprintf(mangled, sizeof(mangled), "%s", node->as.method_call.method_name);
+        else
             snprintf(mangled, sizeof(mangled), "%s$%s", struct_name,
                      node->as.method_call.method_name);
         LLVMValueRef fn = find_fn(ctx, mangled);

src/lexer/lexer.c

@@ -67,6 +67,7 @@ static TokenKind check_keyword(const Token* tok) {
     KW("struct", TOK_STRUCT); KW("type", TOK_TYPE);
     KW("enum", TOK_ENUM);  KW("extend", TOK_EXTEND);  KW("match", TOK_MATCH);
     KW("pub",  TOK_PUB);   KW("mod",  TOK_MOD);  KW("use",  TOK_USE);
+    KW("trait", TOK_TRAIT); KW("Self", TOK_SELF);
     KW("_", TOK_UNDERSCORE);
     KW("true",   TOK_TRUE);   KW("false",  TOK_FALSE);
     #undef KW

src/lexer/token.c

@@ -7,6 +7,7 @@
 static const char* NAMES[] = {
     [TOK_FN] = "fn", [TOK_LET] = "let", [TOK_VAR] = "var", [TOK_IF] = "if", [TOK_GUARD] = "guard",
     [TOK_PUB] = "pub", [TOK_MOD] = "mod", [TOK_USE] = "use",
+    [TOK_TRAIT] = "trait", [TOK_SELF] = "Self",
     [TOK_ELSE] = "else", [TOK_WHILE] = "while", [TOK_FOR] = "for", [TOK_IN] = "in", [TOK_RETURN] = "return",
     [TOK_STRUCT] = "struct", [TOK_TYPE] = "type", [TOK_ENUM] = "enum", [TOK_EXTEND] = "extend",
     [TOK_MATCH] = "match",

src/lexer/token.h

@@ -8,6 +8,7 @@ typedef enum {
     // 关键字
     TOK_FN, TOK_LET, TOK_VAR, TOK_IF, TOK_ELSE, TOK_WHILE, TOK_FOR, TOK_IN, TOK_RETURN, TOK_GUARD,
     TOK_STRUCT, TOK_TYPE, TOK_ENUM, TOK_EXTEND, TOK_MATCH, TOK_PUB, TOK_MOD, TOK_USE,
+    TOK_TRAIT, TOK_SELF,
     // 类型关键字
     TOK_I32, TOK_I64, TOK_U64, TOK_F64, TOK_BOOL, TOK_CHAR, TOK_STR, TOK_VOID,
     // 字面量

src/parser/parser.c

@@ -499,6 +499,14 @@ static TypeInfo parse_type_expr(Parser* p, ErrorInfo* error) {
     const Token* t = peek(p);
     TypeInfo ti = {0};
 
+    // Self 类型（trait 中引用实现者自身类型）
+    if (t->kind == TOK_SELF) {
+        advance(p);
+        ti.kind = TYPE_STRUCT;
+        ti.struct_name = "Self";
+        return ti;
+    }
+
     // 解析基础类型
     if (tok_is_type(t->kind)) {
         advance(p);
@@ -949,8 +957,14 @@ static AstNode* parse_function(Parser* p, bool is_pub, ErrorInfo* error) {
         ret_struct_name = rti.struct_name;
     }
 
-    AstNode* body = parse_block(p, error);
+    // trait 方法签名或普通函数体
+    AstNode* body = NULL;
+    if (match(p, TOK_SEMICOLON)) {
+        body = NULL;  // trait 方法签名，无实现
+    } else {
+        body = parse_block(p, error);
         if (!body) return NULL;
+    }
 
     AstNode** parr = arena_alloc_impl(p->arena, pcount * sizeof(AstNode*));
     memcpy(parr, params, pcount * sizeof(AstNode*));
@@ -1026,7 +1040,31 @@ AstNode* parse(Arena* a, const Token* tokens, size_t count,
         if (peek(&p)->kind == TOK_PUB) {
             is_pub = true; advance(&p);
         }
-        if (peek(&p)->kind == TOK_STRUCT) {
+        if (peek(&p)->kind == TOK_TRAIT) {
+            const Token* tt = advance(&p);
+            const Token* tname = expect(&p, TOK_IDENT, error, "trait 后应为接口名");
+            if (!tname) return NULL;
+            if (!expect(&p, TOK_LBRACE, error, "缺少 '{'")) return NULL;
+            AstNode* methods[64]; int mcount = 0;
+            while (peek(&p)->kind != TOK_RBRACE && !error->message) {
+                if (mcount >= 64) { error->message = "trait 方法过多(最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
+                if (peek(&p)->kind != TOK_FN) { error->message = "trait 内只允许 fn"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
+                // trait 方法只解析签名（body 为空）
+                AstNode* m = parse_function(&p, false, error);
+                if (!m) return NULL;
+                m->as.function.body = NULL;  // trait 方法无实现
+                methods[mcount++] = m;
+                if (peek(&p)->kind == TOK_COMMA) advance(&p);
+            }
+            if (!expect(&p, TOK_RBRACE, error, "缺少 '}'")) return NULL;
+            AstNode** marr = arena_alloc_impl(p.arena, mcount * sizeof(AstNode*));
+            memcpy(marr, methods, mcount * sizeof(AstNode*));
+            // 复用 impl_count 存储 trait（共用计数）
+            if (impl_count >= 64) { error->message = "trait 过多(最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
+            impls[impl_count++] = ast_make_trait_decl(p.arena,
+                arena_strdup_impl(p.arena, tname->start, tname->length),
+                marr, mcount, tok_loc(tt));
+        } else if (peek(&p)->kind == TOK_STRUCT) {
             if (struct_count >= 64) { error->message = "结构体过多 (最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
             structs[struct_count++] = parse_struct_decl(&p, error);
         } else if (peek(&p)->kind == TOK_TYPE) {
@@ -1083,22 +1121,38 @@ AstNode* parse(Arena* a, const Token* tokens, size_t count,
             enums[enum_count++] = enum_decl;
         } else if (peek(&p)->kind == TOK_EXTEND) {
             const Token* i_tok = advance(&p);
-            const Token* st_name = expect(&p, TOK_IDENT, error, "extend 后应为结构体名");
+            const Token* first = expect(&p, TOK_IDENT, error, "extend 后应为结构体名");
-            if (!st_name) return NULL;
+            if (!first) return NULL;
+            const char* trait_name = NULL;
+            const char* struct_name;
+            // extend Trait Struct { ... }（trait 实现：两个标识符）
+            if (peek(&p)->kind == TOK_IDENT) {
+                trait_name = arena_strdup_impl(p.arena, first->start, first->length);
+                struct_name = arena_strdup_impl(p.arena, peek(&p)->start, peek(&p)->length);
+                advance(&p);
+            } else {
+                struct_name = arena_strdup_impl(p.arena, first->start, first->length);
+            }
             if (!expect(&p, TOK_LBRACE, error, "缺少 '{'")) return NULL;
             AstNode* methods[64]; int mcount = 0;
             while (peek(&p)->kind != TOK_RBRACE && !error->message) {
                 if (mcount >= 64) { error->message = "方法过多 (最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
                 if (peek(&p)->kind != TOK_FN) { error->message = "extend 块内只允许 fn"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
-                methods[mcount++] = parse_function(&p, false, error);
+                AstNode* m = parse_function(&p, false, error);
+                if (!m) return NULL;
+                // trait 实现: 方法名 mangled 为 TraitName$methodName
+                if (trait_name) {
+                    char* mn = arena_alloc_impl(p.arena, strlen(trait_name) + strlen(m->as.function.name) + 4);
+                    sprintf(mn, "%s$%s", trait_name, m->as.function.name);
+                    m->as.function.name = mn;
+                }
+                methods[mcount++] = m;
             }
             if (!expect(&p, TOK_RBRACE, error, "缺少 '}'")) return NULL;
             AstNode** m_arr = arena_alloc_impl(p.arena, mcount * sizeof(AstNode*));
             memcpy(m_arr, methods, mcount * sizeof(AstNode*));
             if (impl_count >= 64) { error->message = "extend 块过多 (最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
-            impls[impl_count++] = ast_make_impl_block(p.arena,
+            impls[impl_count++] = ast_make_impl_block(p.arena, struct_name, m_arr, mcount, tok_loc(i_tok));
-                arena_strdup_impl(p.arena, st_name->start, st_name->length),
-                m_arr, mcount, tok_loc(i_tok));
         } else if (peek(&p)->kind == TOK_MOD) {
             advance(&p);
             const Token* mn = expect(&p, TOK_IDENT, error, "mod 后应为模块名");

src/sema/sema.c

@@ -558,6 +558,26 @@ static void analyze_method_call(AstNode* node, Scope* scope, ErrorList* errors,
     snprintf(mangled, sizeof(mangled), "%s$%s", recv_struct,
              node->as.method_call.method_name);
     Symbol* sym = scope_lookup(scope, mangled);
+    // trait 方法 fallback: 搜索所有作用域中以 $method_name 结尾的符号
+    if (!sym || sym->kind != SYM_FUNCTION) {
+        char suffix[256];
+        snprintf(suffix, sizeof(suffix), "$%s", node->as.method_call.method_name);
+        size_t suf_len = strlen(suffix);
+        for (const Scope* sc = scope; sc; sc = sc->parent) {
+            for (Symbol* s = sc->head; s; s = s->next) {
+                if (s->kind == SYM_FUNCTION) {
+                    size_t name_len = strlen(s->name);
+                    if (name_len > suf_len && strcmp(s->name + name_len - suf_len, suffix) == 0) {
+                        sym = s;
+                        // 更新 method_name 为找到的完整函数名（codegen 需要）
+                        node->as.method_call.method_name = s->name;
+                        break;
+                    }
+                }
+            }
+            if (sym) break;
+        }
+    }
     if (!sym || sym->kind != SYM_FUNCTION) {
         error_add(errors, "<sema>", node->loc.line, node->loc.col,
                   "结构体 '%s' 没有方法 '%s'", recv_struct,
@@ -657,6 +677,7 @@ static void analyze_node(AstNode* node, Scope* scope, ErrorList* errors, Arena*
             size_t extra_fn = 0;
             for (size_t i = 0; i < node->as.program.impl_count; i++) {
                 AstNode* impl = node->as.program.impls[i];
+                if (impl->kind == AST_TRAIT_DECL) continue;
                 extra_fn += impl->as.impl_block.method_count;
             }
             if (extra_fn > 0) {
@@ -668,6 +689,7 @@ static void analyze_node(AstNode* node, Scope* scope, ErrorList* errors, Arena*
 
                 for (size_t i = 0; i < node->as.program.impl_count; i++) {
                     AstNode* impl = node->as.program.impls[i];
+                    if (impl->kind == AST_TRAIT_DECL) continue;  // 跳过 trait 声明
                     const char* st_name = impl->as.impl_block.struct_name;
                     // 验证目标结构体存在
                     Symbol* st_sym = scope_lookup_struct(scope, st_name);
@@ -802,6 +824,7 @@ static void analyze_node(AstNode* node, Scope* scope, ErrorList* errors, Arena*
         const char* saved_name = current_return_struct_name;
         current_return_type = node->as.function.return_type;
         current_return_struct_name = node->as.function.return_struct_type_name;
+        if (node->as.function.body)
             analyze_node(node->as.function.body, fn_scope, errors, a);
         current_return_type = saved;
         current_return_struct_name = saved_name;

test/programs/35_trait.l

@@ -0,0 +1,18 @@
+trait Show {
+    fn show(self: Self) -> void;
+}
+
+struct Point { x: i64, y: i64 }
+
+extend Show Point {
+    fn show(self: Point) -> void {
+        print_i64(self.x);
+        print_i64(self.y);
+    }
+}
+
+fn main() -> i64 {
+    let p = Point { x: 10, y: 20 };
+    p.show();
+    return 0;
+}