Fix ImplementInterface (previously GenerateInterfaceStub)

[Booksbaum]

(Mostly port of dotnet/fsharp(VS)/FSharpImplementInterfaceCodeFixProvider -> use InterfaceStubGenerator from dotnet/fsharp instead of custom one)

• Rename GenerateInterfaceStub to ImplementInterface
  • Note: I didn't rename settings (InterfaceStubGeneration, InterfaceStubGenerationObjectIdentifier, InterfaceStubGenerationMethodBody) to not break existing tools
• Fix: Doesn't trigger for types (just for object expressions)
• Fix: Inserts already implemented members too
• Enhancement: CodeFix triggers now on full diagnostic range
  -> cursor can be anywhere Error FS0366 is highlighted. For type that's just interface name, but in object expression that's over the complete object expression
• Add: Implement Interface without type annotation
  • Previously: always with type annotation
  • Now: User can choose between both (-> two CodeFixes)
• Rename title to Implement interface (and Implement interface without type annotation)
  -> align with dotnet/fsharp(VS)/FSharpImplementInterfaceCodeFixProvider and better title (I think)
• Enhancement: Add new members after existing members
  • Question: Should there be a empty line between existing and new members? Or maybe just in type, but not obj expr (-> obj expr: "inline" -> favor shortness)
    • Currently: directly after last member
    • Or get from existing member? -> if empty line between existing members then insert empty line too
      • But: no empty line between new members (-> is from FCS)
• Fix: Issues with triggering of CodeFix, alignment of members, indentation of members
  Some actual fixes: (listed to remind myself to write corresponding tests (✓done) and left here because why not?!...)

  • Fix: Incorrect alignment when new or interface on different line than interface identifier

  • Fix: with gets inserted when existing with on different line than interface identifier

  • Fix: Sometimes no indentation of members in main interface in obj expr

  • Fix: Wrong indentation when implementing sub/additional interfaces in object expression (aligned under interface identifier instead of aligned and indented from interface keyword)

  • Note: There are quite a lot of special cases around alignment and when it is valid vs invalid.

    • Example of special case and difference between interface in type and obj expr:

      type A () =
          // `member` must be behind `interface`
          interface IDisposable with
      //member _.Dispose () = ()            // invalid
      //  member _.Dispose () = ()          // invalid
              member _.Dispose () = ()      // valid
      
      {   new IDisposable with
      //member _.Dispose () = ()            // valid
      //  member _.Dispose () = ()          // valid
              member _.Dispose () = ()      // valid
      }
      let _ = { new IDisposable with
      //member _.Dispose () = ()              // invalid: possible incorrect indentation
      //^^^^^^ should be at line start/no leading spaces (`//` just here to uncomment)
        member _.Dispose () = ()              // valid
          }

      -> used alignment:
      • when existing member: align with existing member
      • otherwise: column of interface or new and then indent a bit further

    There are probably still some cases I didn't catch or aren't covered by tests

  • Note: most (now adjusted) alignments/indentations were valid -- but suboptimal position (too far indented to right)

• Change: member instead of override
  • Reason: FSharp.Compiler.EditorServices.InterfaceStubGenerator uses member
• Internal Restructure:
  • Use FSharp.Compiler.EditorServices.InterfaceStubGenerator instead of FsAutoComplete.InterfaceStubGenerator
    (mostly same -- I think previously EditorServices.InterfaceStubGenerator wasn't public -> copied into FSAC)
  • Remove all InterfaceStub Code from FsAutoComplete.Core
    • I think it fits better into location for CodeFixes. And because InterfaceStubGenerator is now public in FSharp.Compiler.Service (-> most stuff for InterfaceStub in Commands is now unnecessary)
    • Note: This removes public Functionality: FsAutoComplete.Commands.GetInterfaceStub(...) and FsAutoComplete.InterfaceStubGenerator
      -> TODO: needs review
• Add tests
  • Note: quite a lot results have a space after =. But because of linebreaks that's not visible in editors -> use Render Whitespace (or similar) in editor
    • Space comes from FCS

• Add: Setting IndentationSize
  -> fallback when indentation cannot deduced from context
  • default: 4
  • Currently only used in ImplementInterface (-> indentation of members)
  • Should be provided by LSP client
    • TODO: Add to Ionide
      • source? tabSize, .editorconfig, VSCode even auto-detect indentation for each file -> possible to specify per file?
  • In editors it's usually called something like tabSize (in VS Code) -> use TabSize instead? (indent_size in .editorconfig)

[baronfel]

This is great! To answer some of your outstanding questions:

Newlines between members: the current behavior is fine. If a user has fantomas configured (and they should if they're using FSAC), then saving the file will re-format anyway, and their desired configuration will be applied.

Configuration setting: we should expose it in VSCode, but we may be able to get language-specific settings (like editor.tabSize) automatically via the workspace/didChangeConfiguration call. If so that would be a good way to stay notified of user-led changes. I'm not sure if that setting reflects editorconfig though.