Make "decimal" functions more consistent

[aaronfranke]

Previously, "decimals()" in GDScript and "Decimals()" in C# had different behavior. I have renamed the method to "step_decimals()". It was already called that internally. C# is now consistent with core.

[akien-mga]

I don't think decimals is the right name for a function that gives the fractional part of a number - the plural doesn't make sense, it should just be decimal.

That said, we're not keen on breaking compatibility unless there is a strong incentive, so I'm not convinced by these changes.

[CptPotato]

I find the name decimal unfitting for a function that gives you the fractional part of a (decimal) number.
How about naming it frac() or fract() as used in shader languages?

[groud]

I don't even know why we need this function, which can easily be solved by fmod(myvar, 1.0)

[CptPotato]

You're right, though modulo is a bit slower.

[aaronfranke]

Then should I remove the new "decimals()" functionality and instead leave it pointing to "step_decimals" like it was before? That would make it not break compatibility.

EDIT: Done, does not break compatibility anymore

[akien-mga]

IMO it's not worth renaming decimals to step_decimals at this stage, but we can add it in #16863 to the list of methods that we want to rename next time we break compatibility.

[akien-mga]

No longer breaks compat.

If we're deprecating decimals to replace it by step_decimals, I'd add something like this to GDScriptFunctions::call and Expression::exec_func:

ERR_EXPLAIN("GDScript method 'decimals' is deprecated and replaced by 'step_decimals', please update your code accordingly.");
WARN_DEPRECATED

(and then still fallback to step_decimals handling so that it works even if deprecated).

About the addition of DecimalsCount in C#, that's up to @neikeq. I've already mentioned how I feel about adding C#-only features when there's no reason why C# users would need them more than GDScript users. And the whole point of using C# in the first place is to have access to the huge ecosystem of C# libraries, many of which probably cover such method already so that we don't have to reimplement the wheel in core (beyond the compat layer with GDScript).

[akien-mga]

Since 74eefda56 is independent of the renaming proposal, I'd suggest to put it in its own PR so that I can merge it as a bugfix.

[aaronfranke]

Here it is then: #22251

[aaronfranke]

@akien-mga I've added the deprecation warnings as you suggested.

And to clarify, as I mentioned in #22251, the only reason DecimalCount exists is because the C# code had this functionality already, but under the "Decimals" name. It can be removed if requested (and/or in the future & CC @neikeq), and I don't need it personally, I'm just trying to keep the existing functionality.

[akien-mga]

I still don't have a strong opinion on this matter but it's being deprecated the right way, so that's fine with me to merge. If anyone is against it, speak now or never :)

[aaronfranke]

So, just to clarify the justification for this PR:

decimals was a confusing name for this method, to the point that I was confused by it, and the previous C# implementation was wrong. So it's been renamed, and C# is now consistent with Core.

[akien-mga]

Thanks!