refactor: AST Visitor dispatch — sema analyze_expr switch→vtable

新增 src/ast/visit.h/c: AstDispatch 函数指针表 + ast_visit() 统一入口
analyze_expr 的 switch 替换为 dispatch 表, 10 个 handler 通过 SEMA_HANDLER 宏注册
新增 AST 节点: 在 analyze_expr_init() 加一行即可, 编译器会检查函数签名

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/sema/typeck.c

@@ -607,21 +607,46 @@ void analyze_method_call(AstNode* node, Scope* scope, ErrorList* errors, Arena*
         node->type.struct_name = sym->return_struct_type_name;
 }
 
-// === 表达式类型检查（调度器） ===
-void analyze_expr(AstNode* node, Scope* scope, ErrorList* errors, Arena* a) {
-    switch (node->kind) {
-    case AST_LITERAL_EXPR:   break;
-    case AST_IDENT_EXPR:     analyze_ident_expr(node, scope, errors, a);     break;
-    case AST_UNARY_EXPR:     analyze_unary_expr(node, scope, errors, a);     break;
-    case AST_BINARY_EXPR:    analyze_binary_expr(node, scope, errors, a);    break;
-    case AST_CALL_EXPR:      analyze_call_expr(node, scope, errors, a);      break;
-    case AST_FIELD_ACCESS:   analyze_field_access(node, scope, errors, a);   break;
-    case AST_STRUCT_INIT:    analyze_struct_init(node, scope, errors, a);    break;
-    case AST_ENUM_VARIANT:   analyze_enum_variant(node, scope, errors, a);   break;
-    case AST_INDEX_EXPR:     analyze_index_expr(node, scope, errors, a);     break;
-    case AST_METHOD_CALL:    analyze_method_call(node, scope, errors, a);    break;
-    case AST_IF_STMT:        analyze_node(node, scope, errors, a);           break;
-    case AST_BLOCK:          analyze_node(node, scope, errors, a);           break;
-    default: break;
+// === 表达式类型检查（Visitor 调度器） ===
+// 每个 handler 包装函数: (void* ctx, AstNode* node) → 调用实际 handler
+#define SEMA_HANDLER(name) \
+    static void* name##_wrap(void* vctx, AstNode* node) { \
+        SemaCtx* s = (SemaCtx*)vctx; \
+        name(node, s->scope, s->errors, s->a); \
+        return NULL; \
     }
+
+SEMA_HANDLER(analyze_ident_expr)
+SEMA_HANDLER(analyze_unary_expr)
+SEMA_HANDLER(analyze_binary_expr)
+SEMA_HANDLER(analyze_call_expr)
+SEMA_HANDLER(analyze_field_access)
+SEMA_HANDLER(analyze_struct_init)
+SEMA_HANDLER(analyze_enum_variant)
+SEMA_HANDLER(analyze_index_expr)
+SEMA_HANDLER(analyze_method_call)
+SEMA_HANDLER(analyze_node)  // if-expr / block 委托
+
+static AstDispatch sema_dispatch;
+
+void analyze_expr_init(void) {
+    sema_dispatch.ctx = NULL;  // 由 analyze_expr 每次设置
+    // 新增表达式节点: 在此注册 handler, 编译器会警告缺失
+    ast_dispatch_set(&sema_dispatch, AST_IDENT_EXPR,   analyze_ident_expr_wrap);
+    ast_dispatch_set(&sema_dispatch, AST_UNARY_EXPR,   analyze_unary_expr_wrap);
+    ast_dispatch_set(&sema_dispatch, AST_BINARY_EXPR,  analyze_binary_expr_wrap);
+    ast_dispatch_set(&sema_dispatch, AST_CALL_EXPR,    analyze_call_expr_wrap);
+    ast_dispatch_set(&sema_dispatch, AST_FIELD_ACCESS, analyze_field_access_wrap);
+    ast_dispatch_set(&sema_dispatch, AST_STRUCT_INIT,  analyze_struct_init_wrap);
+    ast_dispatch_set(&sema_dispatch, AST_ENUM_VARIANT, analyze_enum_variant_wrap);
+    ast_dispatch_set(&sema_dispatch, AST_INDEX_EXPR,   analyze_index_expr_wrap);
+    ast_dispatch_set(&sema_dispatch, AST_METHOD_CALL,  analyze_method_call_wrap);
+    ast_dispatch_set(&sema_dispatch, AST_IF_STMT,      analyze_node_wrap);
+    ast_dispatch_set(&sema_dispatch, AST_BLOCK,        analyze_node_wrap);
+}
+
+void analyze_expr(AstNode* node, Scope* scope, ErrorList* errors, Arena* a) {
+    SemaCtx sctx = {scope, errors, a};
+    sema_dispatch.ctx = &sctx;
+    ast_visit(&sema_dispatch, node);
 }