Skip to content

allow shortcut begin end syntax inside match and if then else#2744

Merged
EmileTrotignon merged 5 commits intoocaml-ppx:mainfrom
EmileTrotignon:match-beginend-match
Dec 2, 2025
Merged

allow shortcut begin end syntax inside match and if then else#2744
EmileTrotignon merged 5 commits intoocaml-ppx:mainfrom
EmileTrotignon:match-beginend-match

Conversation

@EmileTrotignon
Copy link
Copy Markdown
Collaborator

@EmileTrotignon EmileTrotignon commented Oct 29, 2025

Instead of

match () with
| () -> begin
    match () with
    | () ->
  end
end

you get

match () with
| () ->
    begin match () with
    | () ->
    end
end

Same thing with if-then-else

@EmileTrotignon EmileTrotignon mentioned this pull request Oct 29, 2025
Open
Julow
Julow reviewed Nov 19, 2025
View reviewed changes
Copy link
Copy Markdown
Collaborator

@Julow Julow left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This is an other large change to the formatting of begin .. end. I think we should let the community debate and vote for a formatting that will stay for a while.
Or perhaps, this should be behind an option ?

Comment thread CHANGES.md Outdated

### Changed

- \* allow shortcut `begin end` in `match` cases and `if then else` body. (#2744, @EmileTrotignon)
Copy link
Copy Markdown
Collaborator

@Julow Julow Nov 19, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I think "allow" here is ambiguous. Do you change the formatting for everyone or is here an other allowed formatting ?

Copy link
Copy Markdown
Collaborator Author

@EmileTrotignon EmileTrotignon Nov 19, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I change it everywhere, use would be better

@EmileTrotignon
Copy link
Copy Markdown
Collaborator Author

EmileTrotignon commented Nov 19, 2025

We can make a topic on discuss, I would rather not introduce a new option.

@EmileTrotignon
Copy link
Copy Markdown
Collaborator Author

EmileTrotignon commented Nov 19, 2025

Another thing to point regarding making "big changes" is that after releasing 0.28, we had some negative feedback, but all of it was about bugs/regressions, none of it was people complaining about the intended changes. So I think the reception was clearly positive.

@EmileTrotignon
Copy link
Copy Markdown
Collaborator Author

EmileTrotignon commented Nov 27, 2025

Discuss poll here

@EmileTrotignon
Copy link
Copy Markdown
Collaborator Author

EmileTrotignon commented Dec 1, 2025

Results of the poll are clearly in favour of the change

Julow
Julow approved these changes Dec 1, 2025
View reviewed changes
Copy link
Copy Markdown
Collaborator

@Julow Julow left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Awesome :)

Can you fix the conflicts and merge ?

EmileTrotignon
EmileTrotignon commented Dec 2, 2025
View reviewed changes
Comment thread test/passing/refs.ahrefs/cases_exp_grouping.ml.ref
| A -> begin
match B with
| A ->
begin match B with A -> fooooooooooooo
Copy link
Copy Markdown
Collaborator Author

@EmileTrotignon EmileTrotignon Dec 2, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This is not great but should be fixed by #2745

Copy link
Copy Markdown
Collaborator

@Julow Julow Dec 8, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

What should the formatting be in this case ? Perhaps:

    begin
      match B with A -> fooooooooooooo
    end

@EmileTrotignon EmileTrotignon merged commit 0a805f2 into ocaml-ppx:main Dec 2, 2025
10 of 12 checks passed
Julow added a commit to Julow/opam-repository that referenced this pull request Mar 17, 2026
@Julow
[new release] ocamlformat (4 packages) (0.29.0)
f62a590 
CHANGES:

### Highlight

- \* Support OCaml 5.5 syntax
  (ocaml-ppx/ocamlformat#2772, ocaml-ppx/ocamlformat#2774, ocaml-ppx/ocamlformat#2775, ocaml-ppx/ocamlformat#2777, ocaml-ppx/ocamlformat#2780, ocaml-ppx/ocamlformat#2781, ocaml-ppx/ocamlformat#2782, ocaml-ppx/ocamlformat#2783, @Julow)
  The update brings several tiny changes, they are listed below.

- \* Update Odoc's parser to 3.0 (ocaml-ppx/ocamlformat#2757, @Julow)
  The indentation of code-blocks containing OCaml code is reduced by 2 to avoid
  changing the generated documentation. The indentation within code-blocks is
  now significative in Odoc and shows up in generated documentation.

### Added

- Added option `letop-punning` (ocaml-ppx/ocamlformat#2746, @WardBrian) to control whether
  punning is used in extended binding operators.
  For example, the code `let+ x = x in ...` can be formatted as
  `let+ x in ...` when `letop-punning=always`. With `letop-punning=never`, it
  becomes `let+ x = x in ...`. The default is `preserve`, which will
  only use punning when it exists in the source.
  This also applies to `let%ext` bindings (ocaml-ppx/ocamlformat#2747, @WardBrian).

- Support the unnamed functor parameters syntax in module types
  (ocaml-ppx/ocamlformat#2755, ocaml-ppx/ocamlformat#2759, @Julow)
  ```ocaml
  module type F = ARG -> S
  ```
  The following lines are now formatted as they are in the source file:
  ```ocaml
  module M : (_ : S) -> (_ : S) -> S = N
  module M : S -> S -> S = N
  (* The preceding two lines are no longer turned into this: *)
  module M : (_ : S) (_ : S) -> S = N
  ```

### Fixed

- Fix dropped comment in `(function _ -> x (* cmt *))` (ocaml-ppx/ocamlformat#2739, @Julow)

- \* `cases-matching-exp-indent=compact` does not impact `begin end` nodes that
  don't have a match inside. (ocaml-ppx/ocamlformat#2742, @EmileTrotignon)
  ```ocaml
  (* before *)
  begin match () with
  | () -> begin
    f x
  end
  end
  (* after *)
  begin match () with
  | () -> begin
      f x
    end
  end
  ```

- `Ast_mapper` now iterates on *all* locations inside of Longident.t,
  instead of only some.
  (ocaml-ppx/ocamlformat#2737, @v-gb)

- Remove line break in `M with module N = N (* cmt *)` (ocaml-ppx/ocamlformat#2779, @Julow)

### Internal

- Added information on writing tests to `CONTRIBUTING.md` (ocaml-ppx/ocamlformat#2838, @WardBrian)

### Changed

- indentation of the `end` keyword in a match-case is now always at least 2. (ocaml-ppx/ocamlformat#2742, @EmileTrotignon)
  ```ocaml
  (* before *)
  begin match () with
  | () -> begin
    match () with
    | () -> ()
  end
  end
  (* after *)
  begin match () with
  | () -> begin
    match () with
    | () -> ()

- \* use shortcut `begin end` in `match` cases and `if then else` body. (ocaml-ppx/ocamlformat#2744, @EmileTrotignon)
  ```ocaml
  (* before *)
  match () with
  | () -> begin
      match () with
      | () ->
    end
  end
  (* after *)
  match () with
  | () ->
    begin match () with
      | () ->
    end
  end
  ```

- \* Set the `ocaml-version` to `5.4` by default (ocaml-ppx/ocamlformat#2750, @EmileTrotignon)
  The main difference is that the `effect` keyword is recognized without having
  to add `ocaml-version=5.3` to the configuration.
  In exchange, code that use `effect` as an identifier must use
  `ocaml-version=5.2`.

- The work to support OCaml 5.5 come with several improvements:
  + Improve the indentation of `let structure-item` with the
    `[@ocamlformat "disable"]` attribute.
    `let structure-item` means `let module`, `let open`, `let include` and
    `let exception`.
  + `(let open M in e)[@A]` is turned into `let[@A] open M in e`.
  + Long `let open ... in` no longer exceed the margin.
  + Improve indentation of `let structure-item` within parentheses:
    ```ocaml
    (* before *)
    (let module M = M in
    M.foo)
    (* after *)
    (let module M = M in
     M.foo)
    ```
Julow added a commit to Julow/opam-repository that referenced this pull request Mar 17, 2026
@Julow
[new release] ocamlformat (4 packages) (0.29.0)
e67854d 
CHANGES:

### Highlight

- \* Support OCaml 5.5 syntax
  (ocaml-ppx/ocamlformat#2772, ocaml-ppx/ocamlformat#2774, ocaml-ppx/ocamlformat#2775, ocaml-ppx/ocamlformat#2777, ocaml-ppx/ocamlformat#2780, ocaml-ppx/ocamlformat#2781, ocaml-ppx/ocamlformat#2782, ocaml-ppx/ocamlformat#2783, @Julow)
  The update brings several tiny changes, they are listed below.

- \* Update Odoc's parser to 3.0 (ocaml-ppx/ocamlformat#2757, @Julow)
  The indentation of code-blocks containing OCaml code is reduced by 2 to avoid
  changing the generated documentation. The indentation within code-blocks is
  now significative in Odoc and shows up in generated documentation.

### Added

- Added option `letop-punning` (ocaml-ppx/ocamlformat#2746, @WardBrian) to control whether
  punning is used in extended binding operators.
  For example, the code `let+ x = x in ...` can be formatted as
  `let+ x in ...` when `letop-punning=always`. With `letop-punning=never`, it
  becomes `let+ x = x in ...`. The default is `preserve`, which will
  only use punning when it exists in the source.
  This also applies to `let%ext` bindings (ocaml-ppx/ocamlformat#2747, @WardBrian).

- Support the unnamed functor parameters syntax in module types
  (ocaml-ppx/ocamlformat#2755, ocaml-ppx/ocamlformat#2759, @Julow)
  ```ocaml
  module type F = ARG -> S
  ```
  The following lines are now formatted as they are in the source file:
  ```ocaml
  module M : (_ : S) -> (_ : S) -> S = N
  module M : S -> S -> S = N
  (* The preceding two lines are no longer turned into this: *)
  module M : (_ : S) (_ : S) -> S = N
  ```

### Fixed

- Fix dropped comment in `(function _ -> x (* cmt *))` (ocaml-ppx/ocamlformat#2739, @Julow)

- \* `cases-matching-exp-indent=compact` does not impact `begin end` nodes that
  don't have a match inside. (ocaml-ppx/ocamlformat#2742, @EmileTrotignon)
  ```ocaml
  (* before *)
  begin match () with
  | () -> begin
    f x
  end
  end
  (* after *)
  begin match () with
  | () -> begin
      f x
    end
  end
  ```

- `Ast_mapper` now iterates on *all* locations inside of Longident.t,
  instead of only some.
  (ocaml-ppx/ocamlformat#2737, @v-gb)

- Remove line break in `M with module N = N (* cmt *)` (ocaml-ppx/ocamlformat#2779, @Julow)

### Internal

- Added information on writing tests to `CONTRIBUTING.md` (ocaml-ppx/ocamlformat#2838, @WardBrian)

### Changed

- indentation of the `end` keyword in a match-case is now always at least 2. (ocaml-ppx/ocamlformat#2742, @EmileTrotignon)
  ```ocaml
  (* before *)
  begin match () with
  | () -> begin
    match () with
    | () -> ()
  end
  end
  (* after *)
  begin match () with
  | () -> begin
    match () with
    | () -> ()

- \* use shortcut `begin end` in `match` cases and `if then else` body. (ocaml-ppx/ocamlformat#2744, @EmileTrotignon)
  ```ocaml
  (* before *)
  match () with
  | () -> begin
      match () with
      | () ->
    end
  end
  (* after *)
  match () with
  | () ->
    begin match () with
      | () ->
    end
  end
  ```

- \* Set the `ocaml-version` to `5.4` by default (ocaml-ppx/ocamlformat#2750, @EmileTrotignon)
  The main difference is that the `effect` keyword is recognized without having
  to add `ocaml-version=5.3` to the configuration.
  In exchange, code that use `effect` as an identifier must use
  `ocaml-version=5.2`.

- The work to support OCaml 5.5 come with several improvements:
  + Improve the indentation of `let structure-item` with the
    `[@ocamlformat "disable"]` attribute.
    `let structure-item` means `let module`, `let open`, `let include` and
    `let exception`.
  + `(let open M in e)[@A]` is turned into `let[@A] open M in e`.
  + Long `let open ... in` no longer exceed the margin.
  + Improve indentation of `let structure-item` within parentheses:
    ```ocaml
    (* before *)
    (let module M = M in
    M.foo)
    (* after *)
    (let module M = M in
     M.foo)
    ```
@Julow Julow mentioned this pull request Mar 17, 2026
Merged
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

@Julow Julow Julow approved these changes

Assignees

No one assigned

Labels

None yet

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

2 participants

@EmileTrotignon @Julow