Fix indent of 'fun -> function' arguments

TODO.md

@@ -73,17 +73,3 @@ Argument-list wrapping at toplevel
      in
      aux versions
 ```
-
-`fun -> function` argument
-
-```
-           List.fold_left
-             (fun acc -> function
--               | List [ Atom name; Atom value ] -> (name, value) :: acc
--               | _ -> acc)
-+              | List [ Atom name; Atom value ] -> (name, value) :: acc
-+              | _ -> acc)
-             []
-             l
-           |> List.rev
-```

lib/Fmt_ast.ml

@@ -1538,8 +1538,9 @@ and fmt_function ?(last_arg = false) ?force_closing_paren ~ctx ~ctx0
           | args, typ ->
               ( fmt_fun_args_typ args typ $ space_break
               , []
-              , hvbox (Params.Indent.docked_function_after_fun c.conf ~ctx0)
-              )
+              , hvbox
+                  (Params.Indent.docked_function_after_fun c.conf ~parens
+                     ~ctx0 ~ctx ) )
         in
         let function_ =
           let pre =

lib/Params.ml

@@ -905,13 +905,17 @@ module Indent = struct
 
   let fun_args c = if ocp c then 6 else 4
 
-  let docked_function_after_fun (c : Conf.t) ~ctx0 =
+  let docked_function_after_fun (c : Conf.t) ~parens ~ctx0 ~ctx =
     match ctx0 with
     | Str _ ->
         (* Cases must be 2-indented relative to the [let], even when
            [let_binding_deindent_fun] is on. *)
         if c.fmt_opts.let_binding_deindent_fun.v then 1 else 0
     | _ when ctx_is_infix ctx0 -> 0
+    | _ when ocp c -> (
+      match ctx_is_apply_and_exp_is_arg ~ctx ctx0 with
+      | Some (_, _, false) when parens -> (* Not last argument *) 3
+      | _ -> 2 )
     | _ -> 2
 
   let fun_args_group (c : Conf.t) ~lbl exp =

lib/Params.mli

@@ -232,7 +232,8 @@ module Indent : sig
 
   val fun_type_annot : Conf.t -> int
 
-  val docked_function_after_fun : Conf.t -> ctx0:Ast.t -> int
+  val docked_function_after_fun :
+    Conf.t -> parens:bool -> ctx0:Ast.t -> ctx:Ast.t -> int
 
   val fun_args_group : Conf.t -> lbl:arg_label -> expression -> int