Bail out on reporting unused parameter diagnostic for special paramet…

[mavasani]

…er names

We ignore parameter names that start with an underscore and are optionally followed by an integer, such as _, _1, _2, etc.
This allows bailing out on unused parameters for methods that need a specific signature and are forced to have these parameters. This also serves as a convenient way to suppress instances of unused parameter diagnostic without disabling the diagnostic completely.

Fixes #32851
Fixes #32228

[mavasani]

Tagging @bartdesmet @YairHalberstadt

[YairHalberstadt]

Looks great!
It might be worth adding this as a codefix to the analyser, but if course that could be a seperate pr.

[mavasani]

Tagging @jinujoseph @vatsalyaagrawal for approval and @dotnet/roslyn-ide for further review(s).

[genlu]

So we are creating a naming convention in IDE layer to mark discard parameters w/o compiler support for analysis purposes? Is this something we intend to support officially, or just as a temporary workaround until dotnet/csharplang#2180 is finalized?

[mavasani]

Looks like a reasonable long term solution to me given we don’t expect code bases with wide usages of _1, _2, etc as parameter names.

[mavasani]

@genlu Any further comments? Thanks!

[genlu]

I'm fine with this approach, just two suggestions:

1. consider reporting a info level diagnostic for unused parameter of this pattern
2. maybe change the text of the warning to let people aware of this

Also, we will need to mention this in the VS document when it's up

[mavasani]

consider reporting a info level diagnostic for unused parameter of this pattern

The existing diagnostic is already an info diagnostic, and it seems likely this will just be noise. Lets do this only if we find real customer code bases where such parameter naming is used widely enough for used parameter names.

maybe change the text of the warning to let people aware of this

I think this case is extremely rare, and we see more folks filing such issues, we can change the message. I don't want to make the diagnostic message unnecessarily complex for a rare case. Hopefully, language will also be modified soon enough to allow real discard parameters and we wouldn't need to do anything here.