A better descriptor Id for an F# analyzer

[psfinaki]

Related to this ticket.

Basically we ended up having our compiler and this analyzer often emitting the same diagnostics which causes confusion. The right way is to distinguish them, this is what C# compiler does and what other F# analyzers to here, so it's basically aligning the approach.

Picking IDE0059 because this is the closest match to what we need.

[psfinaki]

cc @dotnet/fsharp-team-msft @T-Gro @tmat

[tmat]

@mavasani Does this look good?

[mavasani]

Tagging @gewarren for confirmation from documentation perspective.

Regarding re-using diagnostic IDs across .NET languages, we are already using the same diagnostic ID across two .NET languages (C# and VB), so using it for F# as well seems reasonable.

However, the IDE0059 flags unused value assignments, not unused variables. There is separate language specific compiler diagnostic ID for the latter. For example https://learn.microsoft.com/en-us/dotnet/csharp/misc/cs0219 for C#. I am not sure IDE0059 is the diagnostic ID that you want for F# unused declarations.

[psfinaki]

@mavasani so this is complicated :)

There are compiler diagnostics and then there are diagnostics from analyzers - serving different purposes. In F#, we have a similar thing to CS0219 and that's FS1182 - the diag number I am replacing in this PR, so that we can distinguish diags in a similar fashion to C#.

A different issue is that in C#, there are different IDE diags for different kinds of "unnecessary" stuff, in particular IDE0058, IDE0059, IDE0060. And that's how it should be, otherwise handling them all is a nightmare for code fixes. Eventually that's what I'd like to have in F# as well because yes now the analyzer and the code fixer try to handle all those cases and do so poorly. What is really handled right now mostly resembles IDE0059 hence the choice.

But yeah I believe we'll add more analyzers in the future to better align with C# here and make life easier for us as well.

[gewarren]

If this is merged, please create an issue in the https://github.com/dotnet/docs repo so I can update the docs for IDE0059.

[mavasani]

What is really handled right now mostly resembles IDE0059 hence the choice.

Alright, I got a bit confused by the analyzer name. It seems fine to me to re-use this ID. Please do create a tracking doc issue and work with @gewarren to get the docs updated appropriately.

[psfinaki]

@gewarren @mavasani there you go.

Thanks! As for the docs, actually it would make sense to update the docs about the other two guys in this folder as well - added this to the ticket above.

[psfinaki]

I don't seem to have the rights to set this for auto-merge - could you let this in? :)