Support bytecode functions in JS_WriteObject

[bnoordhuis]

#975 adds Array.fromAsync as a lazy-loaded bytecode function.

It's actually implemented as a bytecode module with a single exported function that returns the actual Array.fromAsync function.

I did it in this roundabout fashion because JS_WriteObject does not seem capable of directly serializing a bytecode function¹, only when it's embedded in something else, like a script or module.

Things to improve:

1. Support bytecode functions in JS_WriteObject

2. Add a flag to qjsc to compile the input as a function instead of as a script or module.

¹ It's possible ES classes don't work either but I didn't test that

[bnoordhuis]

My notes:

1. it almost works in the sense that JS_WriteObject(JS_MKPTR(JS_TAG_FUNCTION_BYTECODE, p->u.func)) where p->class_id == JS_CLASS_BYTECODE_FUNCTION¹ writes a BC_TAG_FUNCTION_BYTECODE object
2. reading that back produces a JS_TAG_FUNCTION_BYTECODE value
3. you can't JS_Call that value directly, you first need to JS_EvalFunction it
4. the return value from that function you can JS_Call; it's a JS_TAG_OBJECT with p->class_id == JS_CLASS_BYTECODE_FUNCTION...
5. ...which is really just a function object wrapper around the JS_TAG_FUNCTION_BYTECODE value from (2)

¹ Note the inconsistent spelling: function bytecode vs. bytecode function

Getting JS_WriteObject to write the bytecode is easy (see diff) but it also needs to store the class id, otherwise JS_ReadObject doesn't know whether to deserialize it as a regular function, async function, generator, etc.

diff --git a/quickjs.c b/quickjs.c
index ba4cf1a..a5ca972 100644
--- a/quickjs.c
+++ b/quickjs.c
@@ -34421,6 +34421,10 @@ static int JS_WriteObjectRec(BCWriterState *s, JSValueConst obj)
             default:
                 if (is_typed_array(p->class_id)) {
                     ret = JS_WriteTypedArray(s, obj);
+                } else if (js_class_has_bytecode(p->class_id)) {
+                    JSValue fun = JS_MKPTR(JS_TAG_FUNCTION_BYTECODE,
+                                           p->u.func.function_bytecode);
+                    ret = JS_WriteFunctionTag(s, fun);
                 } else {
                     JS_ThrowTypeError(s->ctx, "unsupported object class");
                     ret = -1;