Add warnings for using ++ and -- (standalone expressions that look like increment/decrement operators)

[JeckDev]

Describe the project you are working on

A multiplayer adventure game

Describe the problem or limitation you are having in your project

Coming to GDScript from embedded C and C++, the unary ++ and -- operators are nearly instinctual to me.

Now, #2869 lays out pretty clearly that adding these operators isn't planned. However, the current state of GDScript allows a line such as:

var idx : int = 0
++idx

This will compile and run without warning, but will leave the variable unmodified. It's not hard to imagine a situation in which this introduces subtle and hard to track down bugs, because the coder assumes these operators work and nothing in the editor says otherwise.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

The simplest solution I can imagine is to add a warning when "++" or "--" are encountered.

This notifies the programmer that their assumption about these operators behavior is false.

As far as I know, there's no valid reason to write "++" or "--" besides intending on an increment/decrement, so warning that this doesn't work wouldn't interfere with existing behavior.

(I guess technically someone could write --1 and mean "positive 1", but in this case the warning could be ignored, and besides who does that?)

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

I haven't dived into the code yet, but an easy implementation would be to scan a line for "++" or "--" directly and produce the warning then. More ambiguous parses like "+ +" or "- -" can be left alone.

If this enhancement will not be used often, can it be worked around with a few lines of script?

Obviously this isn't hard to work around. Programmers can just read the docs and see that unary increment/decrement isn't supported.

However, I think that as more people come to Godot from other game engines and other languages, this is a minor change which prevents a minor issue.

Is there a reason why this should be core and not an add-on in the asset library?

As part of GDScript, obviously this should be core.

[Mickeon]

While I do agree, to be pedantic:

This will compile and run without warning

This is not true.

[KillbotGamma]

It looks like there is a warning when using ++ with an int literal, but not when using it with a variable