Re-enable FSharpLint integration

[baronfel]

We should work to update our FSharpLint dependency and verify the integration still works.

• Uncomment in paket.dependencies and paket.references files
• Uncomment methods in FsAutoComplete.Lsp.fs, Commands.fs, and project files as necessary
• Uncomment the fsharplint tests group in the tests' Program.fs
• See what breaks

[Numpsy]

So, what's the current situation with FSharpLint integration (besides FSharpLint itself apparently having not been updated past .NET 5) ?

[baronfel]

It's currently disabled from an IDE integration perspective because the API of the compiler libraries it was built against and the version of those compiler libraries we use have drifted rather significantly. This is a consequence of the lack of API Binary Compatibility in the compiler libraries.

Fantomas has the same problem, but that tool has circumvented the problem by creating an API surface that doesn't directly expose the compiler services, instead delegating to an external process. This model could work with fsharplint as well.

[TheAngryByrd]

Yeah having a layer like Fantomas does currently was my thoughts as well but I don’t have the capacity to maintain another big repo like that.

[Numpsy]

Thanks for the update. Alas, I don't have enough to to do anything more that the odd fix here and there either

[MrLuje]

@baronfel, I'd like to start working on FSharpLint LSP layer.

Previous implementation was using lintParsedSource method with an already built AST & FSharpCheckFileResults
val lintParsedSource : optionalParams:OptionalLintParameters -> parsedFileInfo:ParsedFileInformation -> LintResult

I suppose we could switch to the lintFile method which only take the path to the target file and then use a custom model to avoid using FSC results.
val lintFile : optionalParams:OptionalLintParameters -> filePath:string -> LintResult

The downside is that the file will be parsed at least twice (by FSCA & by FSharpLint); is this fine or is there a better way ?

[baronfel]

This is basically the trade-off that we've made with Fantomas already - luckily parsing files is typically very fast. Typechecking is the really expensive thing, does FSharpLint do that as well?

[TheAngryByrd]

does FSharpLint do that as well?

From what I remember yeah it does. We could share an rsp file so it doesn't need to do additional cracking but unless we're on the same version of FCS, we're not gonna be able to share the typecheck results.