Add bracket indentation semantics to (* *)

[mbottini]

Background: ionide/ionide-fsgrammar#209 and ionide/ionide-fsgrammar#210

This comes from a comment regarding a pull request that I made on the ionide-fsgrammar repository, which removes the (* *) bracket pair from the "brackets" field of language-configuration.json. One issue with doing this is that we lose the bracket-like indentation that VSCode provides by default for all bracket pairs. This pull request re-adds the same semantics to the indentation rules.

In other words, when I hit Enter in the following configuration, cursor location represented by the white block:

(*█*)

It should indent the cursor and then put the *) on the next line with the same indentation level as the (* as follows:

(*
    █
*)

---

When I hit Enter with an unaccompanied (*:

(*█

It should simply indent as follows:

(*
    █

---

Lastly, an unaccompanied *) should outdent. That is,

    *)█

should become

*)█

[MangelMaxime]

Something to note, is that this feature will only be available if user activate FSharp. smartIndent in their setting.

It is not activated by default because the smart indent feature can feel invasive to people and if I remember correctly we can't support all cases correctly.

[MangelMaxime]

If we merge this PR I suppose we are also going to merge https://github.com/ionide/ionide-fsgrammar/pull/210.

Which means we are going to loose auto-indentation for (* ... *) block (due to the grammar PR).

Perhaps we should always compensate (* ... *) block which would lead to something like that:

[!WARNING] Code below is not tested

let activateSmartIndent = "FSharp.smartIndent" |> Configuration.get false

let indentationRules =
    if activateSmartIndent then
        jsOptions<IndentationRule> (fun o ->
            o.increaseIndentPattern <-
                Regex(
                    """^(\s*(module|type|let|static member|member)\b.*=\s*)$|^(\s*(with get|and set)\b.*=.*)$|^(\s*(if|elif|then|else|static member|member|\(\*)).*$"""
                )

            o.decreaseIndentPattern <- Regex("""^(\s*(else|elif|and|\*\))).*$"""))
    else
        jsOptions<IndentationRule> (fun o ->
            o.increaseIndentPattern <-
                Regex(
                    """^(\s*(\(\*)).*$"""
                )

            o.decreaseIndentPattern <- Regex("""^(\s*(\*\))).*$"""))

let setLanguageConfiguration (triggerNotification: bool) =
    // Config always setted
    let config =
        jsOptions<LanguageConfiguration> (fun o ->
            o.onEnterRules <-
                Some
                <| ResizeArray<OnEnterRule>(
                    [|
                        // Doc single-line comment
                        // Example: ///
                        jsOptions<OnEnterRule> (fun rule ->
                            rule.action <-
                                jsOptions<EnterAction> (fun action ->
                                    action.indentAction <- IndentAction.None
                                    action.appendText <- Some "/// ")

                            rule.beforeText <- Regex("^\s*\/{3}.*$"))

                        |]
                )
            o.indentationRules <- Some indentationRules
            )

Doing do mean that we would fix the highlighting coloring thanks to https://github.com/ionide/ionide-fsgrammar/pull/210 but still have indentation for (* ... *) independently of if the user is using smartIndent making this improvements invisible to him.