feat: 复合赋值 += -= *= /= + CHANGELOG 更新

- lexer: 4 个复合赋值 Token (解析时优先于单字符)
- parser: desugar x+=expr → x=x+expr（零 sema/codegen 改动）
- 新增集成测试 09_compound_assign.l (15 12 24 6)
- CHANGELOG 新增 v0.2.0 条目

src/lexer/lexer.c

@@ -104,10 +104,14 @@ Token* lex(Arena* a, const char* source, const char* filename,
             tokens[idx++] = make_token(&l, TOK_STR_LIT, start, len);
         }
         else if (isalpha(c) || c == '_') { tokens[idx++] = lex_ident_or_keyword(&l); }
-        else if (c == '+' && peek_next(&l) != '=') { tokens[idx++] = make_token(&l, TOK_PLUS, l.pos, 1); advance(&l); }
-        else if (c == '-' && peek_next(&l) != '>') { tokens[idx++] = make_token(&l, TOK_MINUS, l.pos, 1); advance(&l); }
+        else if (c == '+' && peek_next(&l) == '=') { tokens[idx++] = make_token(&l, TOK_PLUS_EQ, l.pos, 2); advance(&l); advance(&l); }
+        else if (c == '+') { tokens[idx++] = make_token(&l, TOK_PLUS, l.pos, 1); advance(&l); }
+        else if (c == '-' && peek_next(&l) == '=') { tokens[idx++] = make_token(&l, TOK_MINUS_EQ, l.pos, 2); advance(&l); advance(&l); }
         else if (c == '-' && peek_next(&l) == '>') { tokens[idx++] = make_token(&l, TOK_ARROW, l.pos, 2); advance(&l); advance(&l); }
+        else if (c == '-') { tokens[idx++] = make_token(&l, TOK_MINUS, l.pos, 1); advance(&l); }
+        else if (c == '*' && peek_next(&l) == '=') { tokens[idx++] = make_token(&l, TOK_STAR_EQ, l.pos, 2); advance(&l); advance(&l); }
         else if (c == '*') { tokens[idx++] = make_token(&l, TOK_STAR, l.pos, 1); advance(&l); }
+        else if (c == '/' && peek_next(&l) == '=') { tokens[idx++] = make_token(&l, TOK_SLASH_EQ, l.pos, 2); advance(&l); advance(&l); }
         else if (c == '/') { tokens[idx++] = make_token(&l, TOK_SLASH, l.pos, 1); advance(&l); }
         else if (c == '%') { tokens[idx++] = make_token(&l, TOK_PERCENT, l.pos, 1); advance(&l); }
         else if (c == '=' && peek_next(&l) == '=') { tokens[idx++] = make_token(&l, TOK_EQ_EQ, l.pos, 2); advance(&l); advance(&l); }

src/lexer/token.c

@@ -17,6 +17,7 @@ static const char* NAMES[] = {
     [TOK_LT] = "<", [TOK_GT] = ">", [TOK_LT_EQ] = "<=", [TOK_GT_EQ] = ">=",
     [TOK_AND_AND] = "&&", [TOK_PIPE_PIPE] = "||", [TOK_BANG] = "!",
     [TOK_ARROW] = "->",
+    [TOK_PLUS_EQ] = "+=", [TOK_MINUS_EQ] = "-=", [TOK_STAR_EQ] = "*=", [TOK_SLASH_EQ] = "/=",
     [TOK_LPAREN] = "(", [TOK_RPAREN] = ")",
     [TOK_LBRACE] = "{", [TOK_RBRACE] = "}",
     [TOK_COMMA] = ",", [TOK_COLON] = ":", [TOK_SEMICOLON] = ";",

src/lexer/token.h

@@ -18,6 +18,7 @@ typedef enum {
     TOK_EQ_EQ, TOK_BANG_EQ, TOK_LT, TOK_GT, TOK_LT_EQ, TOK_GT_EQ,
     TOK_AND_AND, TOK_PIPE_PIPE, TOK_BANG,
     TOK_ARROW,
+    TOK_PLUS_EQ, TOK_MINUS_EQ, TOK_STAR_EQ, TOK_SLASH_EQ,
     // 分隔符
     TOK_LPAREN, TOK_RPAREN, TOK_LBRACE, TOK_RBRACE,
     TOK_COMMA, TOK_COLON, TOK_SEMICOLON, TOK_ASSIGN,

src/parser/parser.c

@@ -277,6 +277,37 @@ static AstNode* parse_statement(Parser* p, ErrorInfo* error) {
             value, name->line, name->col);
     }
 
+    // 复合赋值: ident += expr  →  ident = ident + expr
+    if (t->kind == TOK_IDENT) {
+        TokenKind next_kind = (t + 1)->kind;
+        if (next_kind >= TOK_PLUS_EQ && next_kind <= TOK_SLASH_EQ) {
+            const Token* name = advance(p);  // 消费标识符
+            TokenKind comp_op = advance(p)->kind;
+
+            BinaryOp binop;
+            switch (comp_op) {
+                case TOK_PLUS_EQ:  binop = OP_ADD; break;
+                case TOK_MINUS_EQ: binop = OP_SUB; break;
+                case TOK_STAR_EQ:  binop = OP_MUL; break;
+                case TOK_SLASH_EQ: binop = OP_DIV; break;
+                default: break;
+            }
+
+            AstNode* rhs = parse_expr(p, error);
+            if (!rhs) return NULL;
+            if (!expect(p, TOK_SEMICOLON, error, "缺少 ';'")) return NULL;
+
+            AstNode* lhs_ident = ast_make_ident(p->arena,
+                arena_strdup_impl(p->arena, name->start, name->length),
+                name->line, name->col);
+            AstNode* bin_expr = ast_make_binary(p->arena, binop, lhs_ident, rhs,
+                name->line, name->col);
+            return ast_make_assign(p->arena,
+                arena_strdup_impl(p->arena, name->start, name->length),
+                bin_expr, name->line, name->col);
+        }
+    }
+
     // 表达式语句
     AstNode* expr = parse_expr(p, error);
     if (!expr) return NULL;