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@Julow Julow commented Oct 24, 2025

Auto-formatter for OCaml code

CHANGES:

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Added

Deprecated

Changed

Fixed

….28.1)

CHANGES:

### Highlight

- \* Support for OCaml 5.4
  (ocaml-ppx/ocamlformat#2717, ocaml-ppx/ocamlformat#2720, ocaml-ppx/ocamlformat#2732, ocaml-ppx/ocamlformat#2733, ocaml-ppx/ocamlformat#2735, @Julow, @Octachron, @cod1r, @EmileTrotignon)
  OCamlformat now supports OCaml 5.4 syntax.
  Module packing of the form `((module M) : (module S))` are no longer
  rewritten to `(module M : S)` because these are now two different syntaxes.

- \* Reduce indentation after `|> map (fun` (ocaml-ppx/ocamlformat#2694, @EmileTrotignon)
  Notably, the indentation no longer depends on the length of the infix
  operator, for example:
  ```ocaml
  (* before *)
  v
  |>>>>>> map (fun x ->
              x )
  (* after *)
  v
  |>>>>>> map (fun x ->
      x )
  ```
  `@@ match` can now also be on one line.

### Added

- Added option `module-indent` option (ocaml-ppx/ocamlformat#2711, @HPRIOR) to control the indentation
  of items within modules. This affects modules and signatures. For example,
  module-indent=4:
  ```ocaml
  module type M = sig
      type t

      val f : (string * int) list -> int
  end
  ```

- `exp-grouping=preserve` is now the default in `default` and `ocamlformat`
  profiles. This means that its now possible to use `begin ... end` without
  tweaking ocamlformat. (ocaml-ppx/ocamlformat#2716, @EmileTrotignon)

### Deprecated

- Starting in this release, ocamlformat can use cmdliner >= 2.0.0. When that is
  the case, the tool no longer accepts unambiguous option names prefixes. For
  example, `--max-iter` is not accepted anymore, you have to pass the full
  option `--max-iters`. This does not apply to the keys in the `.ocamlformat`
  configuration files, which have always required the full name.
  See dbuenzli/cmdliner#200.
  (ocaml-ppx/ocamlformat#2680, @emillon)

### Changed

- \* The formatting of infix extensions is now consistent with regular
  formatting by construction. This reduces indentation in `f @@ match%e`
  expressions to the level of indentation in `f @@ match`. Other unknown
  inconsistencies might also be fixed. (ocaml-ppx/ocamlformat#2676, @EmileTrotignon)

- \* The spacing of infix attributes is now consistent across keywords. Every
  keyword but `begin` `function`, and `fun` had attributes stuck to the keyword:
  `match[@A]`, but `fun [@A]`. Now its also `fun[@A]`. (ocaml-ppx/ocamlformat#2676, @EmileTrotignon)

- \* The formatting of`let a = b in fun ...` is now consistent with other
  contexts like `a ; fun ...`. A check for the syntax `let a = fun ... in ...`
  was made more precise. (ocaml-ppx/ocamlformat#2705, @EmileTrotignon)

- \* `|> begin`, `~arg:begin`, `begin if`, `lazy begin`, `begin match`,
  `begin fun` and `map li begin fun`  can now be printed on the same line, with
  one less indentation level for the body of the inner expression.
  (ocaml-ppx/ocamlformat#2664, ocaml-ppx/ocamlformat#2666, ocaml-ppx/ocamlformat#2671, ocaml-ppx/ocamlformat#2672, ocaml-ppx/ocamlformat#2681, ocaml-ppx/ocamlformat#2685, ocaml-ppx/ocamlformat#2693, @EmileTrotignon)
  For example :
  ```ocaml
  (* before *)
  begin
    fun x ->
      some code
  end
  (* after *)
  begin fun x ->
    some code
  end
  ```

- \* `break-struct=natural` now also applies to `sig ... end`. (ocaml-ppx/ocamlformat#2682, @EmileTrotignon)

### Fixed

- Fixed `wrap-comments=true` not working with the janestreet profile (ocaml-ppx/ocamlformat#2645, @Julow)
  Asterisk-prefixed comments are also now formatted the same way as with the
  default profile.

- Fixed `nested-match=align` not working with `match%ext` (ocaml-ppx/ocamlformat#2648, @EmileTrotignon)

- Fixed the AST generated for bindings of the form `let pattern : type = function ...`
  (ocaml-ppx/ocamlformat#2651, @v-gb)

- Print valid syntax for the corner case (1).a (ocaml-ppx/ocamlformat#2653, @v-gb)

- `Ast_mapper.default_mapper` now iterates on the location of `in` in `let+ .. in ..`
  (ocaml-ppx/ocamlformat#2658, @v-gb)

- Fix missing parentheses in `let+ (Cstr _) : _ = _` (ocaml-ppx/ocamlformat#2661, @Julow)
  This caused a crash as the generated code wasn't valid syntax.

- Fix bad indentation of `let%ext { ...` (ocaml-ppx/ocamlformat#2663, @EmileTrotignon)
  with `dock-collection-brackets` enabled.

- ocamlformat is now more robust when used as a library to print modified ASTs
  (ocaml-ppx/ocamlformat#2659, @v-gb)

- Fix crash due to edge case with asterisk-prefixed comments (ocaml-ppx/ocamlformat#2674, @Julow)

- Fix crash when formatting `mld` files that cannot be lexed as ocaml (e.g.
  containing LaTeX or C code) (ocaml-ppx/ocamlformat#2684, @emillon)

- \* Fix double parens around module constraint in functor application :
  `module M = F ((A : T))` becomes `module M = F (A : T)`. (ocaml-ppx/ocamlformat#2678, @EmileTrotignon)

- Fix misplaced `;;` due to interaction with floating doc comments.
  (ocaml-ppx/ocamlformat#2691, @EmileTrotignon)

- The formatting of attributes of expression is now aware of the attributes
  infix or postix positions: `((fun [@A] x -> y) [@b])` is formatted without
  moving attributes. (ocaml-ppx/ocamlformat#2676, @EmileTrotignon)

- `begin%e ... end` and `begin [@A] ... end` nodes are always preserved.
  (ocaml-ppx/ocamlformat#2676, @EmileTrotignon)

- `begin end` syntax for `()` is now preserved. (ocaml-ppx/ocamlformat#2676, @EmileTrotignon)

- Fix a crash on `type 'a t = A : 'a. {a: 'a} -> 'a t`. (ocaml-ppx/ocamlformat#2710, @EmileTrotignon)

- Fix a crash where `type%e nonrec t = t` was formatted as `type nonrec%e t = t`,
  which is invalid syntax. (ocaml-ppx/ocamlformat#2712, @EmileTrotignon)

- Fix commandline parsing being quadratic in the number of arguments
  (ocaml-ppx/ocamlformat#2724, @let-def)

- \* Fix `;;` being added after a documentation comment (ocaml-ppx/ocamlformat#2683, @EmileTrotignon)
  This results in more `;;` being inserted, for example:
  ```ocaml
  (* before *)
  print_endline "foo"
  let a = 3

  (* after *)
  print_endline "foo" ;;
  let a = 3
  ```

- Fix dropped comment in `if then (* comment *) begin .. end` (ocaml-ppx/ocamlformat#2734, @Julow)
@smorimoto smorimoto merged commit 6c1b386 into ocaml:master Oct 24, 2025
2 of 4 checks passed
@Julow
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Julow commented Oct 24, 2025

Thanks!

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2 participants