Add new destruct-line code action

[awilliambauer]

Merlin-destruct is made more useful by adding a new LSP code-action called destruct-line which does some pre- and post-processing surrounding a call to Merlin-destruct.

This new code-action can be invoked on a line where the user has typed match... or match...with, or within an incomplete match statement on a line with an existing case. When invoked, the code-action will fill in the remaining cases of the match. This means that in VSCode, if you have one of the following lines, you can hit C-. from anywhere on the line to achieve the corresponding expansion.

Supposing x is a bool, then the line

match x

expands to

match x with
| false -> _
| true -> _

Supposing get_card returns a card_value variant, then the line

match get_card (int_of_string s) with

expands to

match get_card (int_of_string s) with
| Ace -> _
| King -> _
| Queen -> _
| Jack -> _
| Number _ -> _

Or supposing you've already filled in

match get_card (int_of_string s) with
| King -> "Face Card"
| Queen -> "Face Card"

then destruct-line on either the King or Queen line will produce

match get_card (int_of_string s) with
| King -> "Face Card"
| Queen -> "Face Card"
| Ace -> _
| Jack -> _
| Number _ -> _

In addition, the code action detects a sub-case of the | x -> y form, where the cursor is on an underscore within x.

The following expansions result from repeated applications of destruct-line:

let zip (type a b) (xs : a list) (ys : b list) : (a * b) list =
  match xs, ys

After code action is invoked anywhere on the match line:

let zip (type a b) (xs : a list) (ys : b list) : (a * b) list =
  match (xs, ys) with
  | (_, _) -> _

After code action is invoked on the first underscore:

let zip (type a b) (xs : a list) (ys : b list) : (a * b) list =
  match (xs, ys) with
  | ([], _) -> _
  | (_::_, _) -> _

After code action is invoked on the first underscore:

let zip (type a b) (xs : a list) (ys : b list) : (a * b) list =
  match (xs, ys) with
  | ([], []) -> _
  | ([], _::_) -> _
  | (_::_, _) -> _

After code action is invoked on the second-to-last underscore:

let zip (type a b) (xs : a list) (ys : b list) : (a * b) list =
  match (xs, ys) with
  | ([], []) -> _
  | ([], _::_) -> _
  | (_::_, []) -> _
  | (_::_, _::_) -> _

[rgrinberg]

LGTM, but I'd like to avoid Re2. Are you in favor of replacing it with ocaml-re?

[rgrinberg]

Alright, I managed to get rid of re2 in favor of re. core was unused so I just got rid of it. base can stay and we should feel free to use it to replace stdune.

[coveralls]

Pull Request Test Coverage Report for Build 4263

Details

• 100 of 115 (86.96%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 21.496%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
ocaml-lsp-server/src/code_actions/action_destruct_line.ml	98	113	86.73%

Totals
Change from base Build 4260:	0.3%
Covered Lines:	5246
Relevant Lines:	24405

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💛 - Coveralls