Improve deserializer error message for bytecode

Don't raise a "invalid tag 12" exception when encountering bytecode
and JS_READ_OBJ_BYTECODE is not set, because no one knows what "tag 12"
means without looking it up, not even quickjs maintainers.

quickjs-libc.c

@@ -837,6 +837,7 @@ static JSValue js_evalScript(JSContext *ctx, JSValue this_val,
     JSValue ret;
     JSValue options_obj;
     BOOL backtrace_barrier = FALSE;
+    BOOL compile_only = FALSE;
     BOOL is_async = FALSE;
     int flags;
 
@@ -845,6 +846,9 @@ static JSValue js_evalScript(JSContext *ctx, JSValue this_val,
         if (get_bool_option(ctx, &backtrace_barrier, options_obj,
                             "backtrace_barrier"))
             return JS_EXCEPTION;
+        if (get_bool_option(ctx, &compile_only, options_obj,
+                            "compile_only"))
+            return JS_EXCEPTION;
         if (get_bool_option(ctx, &is_async, options_obj,
                             "async"))
             return JS_EXCEPTION;
@@ -860,6 +864,8 @@ static JSValue js_evalScript(JSContext *ctx, JSValue this_val,
     flags = JS_EVAL_TYPE_GLOBAL;
     if (backtrace_barrier)
         flags |= JS_EVAL_FLAG_BACKTRACE_BARRIER;
+    if (compile_only)
+        flags |= JS_EVAL_FLAG_COMPILE_ONLY;
     if (is_async)
         flags |= JS_EVAL_FLAG_ASYNC;
     ret = JS_Eval(ctx, str, len, "<evalScript>", flags);

quickjs.c

@@ -35473,12 +35473,14 @@ static JSValue JS_ReadObjectRec(BCReaderState *s)
         break;
     case BC_TAG_FUNCTION_BYTECODE:
         if (!s->allow_bytecode)
-            goto invalid_tag;
+            goto no_allow_bytecode;
         obj = JS_ReadFunctionTag(s);
         break;
     case BC_TAG_MODULE:
-        if (!s->allow_bytecode)
-            goto invalid_tag;
+        if (!s->allow_bytecode) {
+        no_allow_bytecode:
+            return JS_ThrowSyntaxError(ctx, "no bytecode allowed");
+        }
         obj = JS_ReadModule(s);
         break;
     case BC_TAG_OBJECT:

tests/test_bjson.js

@@ -1,3 +1,4 @@
+import * as std from "std";
 import * as bjson from "bjson";
 import { assert } from "./assert.js";
 
@@ -227,6 +228,25 @@ function bjson_test_symbol()
     assert(o, r);
 }
 
+function bjson_test_bytecode()
+{
+    var buf, o, r, e;
+
+    o = std.evalScript(";(function f(o){ return o.i })", {compile_only: true});
+    buf = bjson.write(o, /*JS_WRITE_OBJ_BYTECODE*/(1 << 0));
+    try {
+        bjson.read(buf, 0, buf.byteLength);
+    } catch (_e) {
+        e = _e;
+    }
+    assert(String(e), "SyntaxError: no bytecode allowed");
+
+    // can't really do anything with |o| at the moment,
+    // no way to pass it to JS_EvalFunction
+    o = bjson.read(buf, 0, buf.byteLength, /*JS_READ_OBJ_BYTECODE*/(1 << 0));
+    assert(String(o), "[function bytecode]");
+}
+
 function bjson_test_fuzz()
 {
     var corpus = [
@@ -277,6 +297,7 @@ function bjson_test_all()
     bjson_test_map();
     bjson_test_set();
     bjson_test_symbol();
+    bjson_test_bytecode();
     bjson_test_fuzz();
 }