Improvements/Fixes for Unused Declarations

[Booksbaum]

Change: Get Unused Declarations from FCS

• -> remove custom UnusedDeclarationAnalyzer

Enhancement: mark more elements (like functions & members) as unused

• prev: just variables & parameters
• provided by FCS (see change above)
• Fixes Unused marking missing for private, unused functions #832

Enhancement/Change: Unused Diagnostic now always contains Code FSAC0003

• prev: only some unused diags contained FSAC0003.
  Code was used to differentiate between this value (-> only replace with _ CodeFix) and other values (-> both Replace & prefix CodeFixes). That's now determined inside RenameUnusedValue CodeFix -> all diags can be FSAC0003
• As a result: NotificationEvent.UnusedDeclarations(file, decls) -> decls is now just range[] (prev: (range*bool)[])

Fixes for RenameUnusedValue CodeFix:

• Fix: name in backticks triggers "Prefix with _" CodeFix. But let _``hello world`` = ... is invalid.
  -> Prefix CodeFix doesn't trigger any more for backticks. Replace with _ still does.
• Fix_ish: private variable triggers "Replace with _" CodeFix. But let private _ = ... is invalid (private is part of named SynPat, not part of let binding or outer SynPat)
  • Issue: SynPat.Named range doesn't include access modifier. And SynAccess doesn't include a range. (At least in FCS version currently used in FSAC. Range was introduced in Add range of access to SyntaxTree. dotnet/fsharp#13304 )
  • -> Instead of replacing the modifier too, I just disable the Replace CodeFix for cases with access modifier.
    Once there is a FCS with ranges for SynAccess it should be trivial to enable Replace CodeFix again (-> see code and corresponding tests)

• Note: Prefix/Replace with _ CodeFix still only triggers for unused value bindings, but not functions or members.
  I don't think you ever want a _-prefixed function or member, but instead should either remove or make it public -> no prefix CodeFix (and replace with _ is invalid for functions/members)

[baronfel]

awesome

You note that the SynAccess range isn't present in our FCS version - is it in FCS 41.0.5 (the latest release)? If so we should update that sometime this week, because proj-info just updated to it and I'm planning on updating the proj-info dependency in this repo.

[Booksbaum]

FSAC is already at 41.0.5

I think SynAccess.range will be included in the next major FCS version (42?) (including other AST changed like necessary to remove ServiceParseTreeWalk again)