Parser exception on lone comment

[EJMFarrow]

Steps to trigger:

• Edit a question.
• Set question variables to /* test */
• Attempt to save.

Result:

Exception - maxima_parser_utils::do_parse(): Return value must be of type MP_Node, null returned

Occurs in 4.11.1; not a problem in 4.10.0. (Maxima 5.46 in both cases, I think.)

[aharjula]

I guess we should catch this before it goes to the parser, or have logic that handles the result from the parser accordingly. If I recall correctly, we do not send empty strings (after trimming) to the parser and consider them null; a string consisting of just comments should be the same.

The new parser (in dev) shares logic with the Rust version, and that has a defined behaviour for this (the third example there is running with comment collection off). I do suggest we follow that and make things behave like it does, i.e., return an empty MP_Root instead of null.

[sangwinc]

Thanks @aharjula that's really helpful.