Refactoring for _.Property / _.MethodCall() / _.IndexerAccess[idx] shorthand for accessor functions

[edgarfgp]

Now that #13907 is merged would be good to have code-fix for this

• Design

• Implementation

• From fun x -> x.Foo to _.Foo and maybe the other way around too ?

// From
let a5 : {| Foo : int -> {| X : string |} |} -> string = fun x -> x.Foo(5).X

// To
let a5 : {| Foo : int -> {| X : string |} |} -> string = _.Foo(5).X

// From
let a6 = [1] |> List.map(fun x -> x.ToString())

// To
let a6 = [1] |> List.map _.ToString()

[psfinaki]

You mean something like fixing _.Length() to _.Length?

[edgarfgp]

You mean something like fixing _.Length() to _.Length?

Updated the description clarifying the quick-fix intent. Sorry that it was not really clear

[psfinaki]

Ohh okay. So AFAIU there is no diagnostic for "hey, this is an old way of doing stuff, use the new one" - hence this will need an analyzer first.

[T-Gro]

Code-fixes react to diagnostics, i.e. the code would have to be producing at least a warning or similar in the first place.
An action which chages the "style" without affecting behavior falls into the Refactoring bucket.

[vzarytovskii]

It should be a code action which is a result of code analyzer.

[edgarfgp]

Perfect 👍🏻. Seem a good candidate for the upcoming Analyser sdk

[psfinaki]

Well it could be done similarly to this: #16079

So analyzer + code fix. Refactorings are more invasive code actions :)

[T-Gro]

No, that is not the difference. They can both have various levels of invasiveness.

Codefix needs a diagnostics first a should change wrong code into incorrect one, refactoring does not and can typically exists two times in symmetrical variants.

It is fine if a 3rd party creates their own analyzer, but in my opinion this would be wrong:
It would be telling that existing lambda syntax (fun x -> x.MethodCall().Property.Indexer[42]) needs a warning.

The underscore dot lambda syntax is not meant as a general replacement, the old lambda syntax is still correct and considered good F# code.

Hence: It should be a refactoring, not fixing a diagnostical issue.