Improve parsing error messages (#405)

- output more informative error messages in `js_parse_expect`.

The previous code was bogus:
```
    return js_parse_error(s, "expecting '%c'", tok);
```
this was causing a bug on `eval("do;")` where `tok` is `TOK_WHILE` (-70, 0xBA)
creating an invalid UTF-8 encoding (lone trailing byte).
This would ultimately have caused a failure in `JS_ThrowError2` if `JS_NewString`
failed when converting the error message to a string if the conversion detected the invalid
UTF-8 encoding and throwed an error (it currently does not, but should).

- test for `JS_NewString` failure in `JS_ThrowError2`
- test for `JS_FreeCString` failure in run-test262.c
- add more test cases

quickjs.c

@@ -6635,7 +6635,7 @@ static JSValue JS_ThrowError2(JSContext *ctx, JSErrorEnum error_num,
                               const char *fmt, va_list ap, BOOL add_backtrace)
 {
     char buf[256];
-    JSValue obj, ret;
+    JSValue obj, ret, msg;
 
     vsnprintf(buf, sizeof(buf), fmt, ap);
     obj = JS_NewObjectProtoClass(ctx, ctx->native_error_proto[error_num],
@@ -6644,10 +6644,14 @@ static JSValue JS_ThrowError2(JSContext *ctx, JSErrorEnum error_num,
         /* out of memory: throw JS_NULL to avoid recursing */
         obj = JS_NULL;
     } else {
-        JS_DefinePropertyValue(ctx, obj, JS_ATOM_message,
-                               JS_NewString(ctx, buf),
+        msg = JS_NewString(ctx, buf);
+        if (JS_IsException(msg))
+            msg = JS_NewString(ctx, "Invalid error message");
+        if (!JS_IsException(msg)) {
+            JS_DefinePropertyValue(ctx, obj, JS_ATOM_message, msg,
                                    JS_PROP_WRITABLE | JS_PROP_CONFIGURABLE);
         }
+    }
     if (add_backtrace) {
         build_backtrace(ctx, obj, NULL, 0, 0, 0);
     }
@@ -18633,11 +18637,33 @@ int __attribute__((format(printf, 2, 3))) js_parse_error(JSParseState *s, const
 
 static int js_parse_expect(JSParseState *s, int tok)
 {
-    if (s->token.val != tok) {
-        /* XXX: dump token correctly in all cases */
-        return js_parse_error(s, "expecting '%c'", tok);
-    }
+    char buf[ATOM_GET_STR_BUF_SIZE];
+
+    if (s->token.val == tok)
         return next_token(s);
+
+    switch(s->token.val) {
+    case TOK_EOF:
+        return js_parse_error(s, "Unexpected end of input");
+    case TOK_NUMBER:
+        return js_parse_error(s, "Unexpected number");
+    case TOK_STRING:
+        return js_parse_error(s, "Unexpected string");
+    case TOK_TEMPLATE:
+        return js_parse_error(s, "Unexpected string template");
+    case TOK_REGEXP:
+        return js_parse_error(s, "Unexpected regexp");
+    case TOK_IDENT:
+        return js_parse_error(s, "Unexpected identifier '%s'",
+                              JS_AtomGetStr(s->ctx, buf, sizeof(buf),
+                                            s->token.u.ident.atom));
+    case TOK_ERROR:
+        return js_parse_error(s, "Invalid or unexpected token");
+    default:
+        return js_parse_error(s, "Unexpected token '%.*s'",
+                              (int)(s->buf_ptr - s->token.ptr),
+                              (const char *)s->token.ptr);
+    }
 }
 
 static int js_parse_expect_semi(JSParseState *s)

run-test262.c

@@ -1299,12 +1299,16 @@ static int eval_buf(JSContext *ctx, const char *buf, size_t buf_len,
                 const char *msg;
 
                 msg = JS_ToCString(ctx, exception_val);
+                if (msg == NULL) {
+                    ret = -1;
+                } else {
                     error_class = strdup_len(msg, strcspn(msg, ":"));
                     if (!str_equal(error_class, error_type))
                         ret = -1;
                     free(error_class);
                     JS_FreeCString(ctx, msg);
                 }
+            }
         } else {
             ret = -1;
         }

tests/test_language.js

@@ -20,7 +20,14 @@ function assert_throws(expected_error, func, message)
     var err = false;
     var msg = message ? " (" + message + ")" : "";
     try {
+        switch (typeof func) {
+        case 'string':
+            eval(func);
+            break;
+        case 'function':
             func();
+            break;
+        }
     } catch(e) {
         err = true;
         if (!(e instanceof expected_error)) {
@@ -546,7 +553,7 @@ function test_function_expr_name()
 
 function test_expr(expr, err) {
     if (err)
-        assert_throws(err, () => eval(expr), `for ${expr}`);
+        assert_throws(err, expr, `for ${expr}`);
     else
         assert(1, eval(expr), `for ${expr}`);
 }
@@ -608,6 +615,26 @@ function test_number_literals()
     test_expr('0.a', SyntaxError);
 }
 
+function test_syntax()
+{
+    assert_throws(SyntaxError, "do");
+    assert_throws(SyntaxError, "do;");
+    assert_throws(SyntaxError, "do{}");
+    assert_throws(SyntaxError, "if");
+    assert_throws(SyntaxError, "if\n");
+    assert_throws(SyntaxError, "if 1");
+    assert_throws(SyntaxError, "if \0");
+    assert_throws(SyntaxError, "if ;");
+    assert_throws(SyntaxError, "if 'abc'");
+    assert_throws(SyntaxError, "if `abc`");
+    assert_throws(SyntaxError, "if /abc/");
+    assert_throws(SyntaxError, "if abc");
+    assert_throws(SyntaxError, "if abc\u0064");
+    assert_throws(SyntaxError, "if abc\\u0064");
+    assert_throws(SyntaxError, "if \u0123");
+    assert_throws(SyntaxError, "if \\u0123");
+}
+
 test_op1();
 test_cvt();
 test_eq();
@@ -629,3 +656,4 @@ test_argument_scope();
 test_function_expr_name();
 test_reserved_names();
 test_number_literals();
+test_syntax();