Wrap short fun after a let with the janestreet profile

CHANGES.md

@@ -58,6 +58,7 @@ profile. This started with version 0.26.0.
   The attribute is moved from `begin .. end [@attr]` to `begin [@attr] .. end`.
 - Fix missing parentheses around `let .. in [@attr]` (#2564, @Julow)
 - Display `a##b` instead of `a ## b` and similarly for operators that start with # (#2580, @v-gb)
+- Fix formatting of short `fun` expressions with the janestreet profile (#2593, @Julow)
 
 ### Changes
 - The location of attributes for structure items is now tracked and preserved. (#2247, @EmileTrotignon)

lib/Fmt_ast.ml

@@ -1509,7 +1509,7 @@ and fmt_function ?(last_arg = false) ?force_closing_paren ~ctx ~ctx0
         let head = fmt_fun_args_typ args typ in
         let body ~pro = pro $ fmt_expression c (sub_exp ~ctx body) in
         let box, closing_paren_offset =
-          Params.Exp.box_fun_expr c.conf ~source:c.source ~ctx0 ~ctx ~parens
+          Params.Exp.box_fun_expr c.conf ~source:c.source ~ctx0 ~ctx
         in
         let closing_paren_offset =
           if should_box then closing_paren_offset else ~-2

lib/Params.ml

@@ -213,7 +213,7 @@ module Exp = struct
         ( kw_in_box
         $ hvbox_if should_box_args 0 (args $ fmt_opt annot $ fmt_opt epi) )
 
-  let box_fun_expr (c : Conf.t) ~source ~ctx0 ~ctx ~parens =
+  let box_fun_expr (c : Conf.t) ~source ~ctx0 ~ctx =
     let indent =
       if ctx_is_rhs_of_infix ~ctx0 ~ctx then 0
       else if Poly.equal c.fmt_opts.function_indent_nested.v `Always then
@@ -244,14 +244,7 @@ module Exp = struct
       else 2
     in
     let name = "Params.box_fun_expr" in
-    let mkbox =
-      match ctx0 with
-      | Str _ | Lb _ -> hvbox
-      | _ ->
-          (* JS: The body of a [fun] must break if the intro is too large,
-             except if the [fun] is small and parenthesed. *)
-          if ocp c && not parens then hvbox else hovbox
-    in
+    let mkbox = if ctx_is_let_or_fun ~ctx ctx0 then hvbox else hovbox in
     (mkbox ~name indent, ~-indent)
 
   (* if the function is the last argument of an apply and no other arguments

lib/Params.mli

@@ -58,7 +58,6 @@ module Exp : sig
     -> source:Source.t
     -> ctx0:Ast.t
     -> ctx:Ast.t
-    -> parens:bool
     -> (Fmt.t -> Fmt.t) * int
   (** return a box with an indent and minus the value of the indent to be used for a closing parenthesis *)
 

test/passing/tests/js_source.ml

@@ -8241,3 +8241,11 @@ let _ =
     (* foooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo *)
   else f
 ;;
+
+let _ =
+  match ids_queue with
+  | Some q ->
+    (* this is more efficient than a linear scan of [ids] *)
+    fun id -> not (Ident.HashQueue.mem q id)
+  | None -> fun id -> not (List.mem ~equal:Ident.equal ids id)
+;;

test/passing/tests/js_source.ml.err

@@ -3,4 +3,4 @@ Warning: tests/js_source.ml:9564 exceeds the margin
 Warning: tests/js_source.ml:9668 exceeds the margin
 Warning: tests/js_source.ml:9727 exceeds the margin
 Warning: tests/js_source.ml:9810 exceeds the margin
-Warning: tests/js_source.ml:10309 exceeds the margin
+Warning: tests/js_source.ml:10308 exceeds the margin

test/passing/tests/js_source.ml.ocp

@@ -10235,8 +10235,7 @@ let _ =
     foooooooooooooooooo
     foooooooooooooooooo
     foooooooooooooooooo
-    foooooooooooooooooo ->
-    ()
+    foooooooooooooooooo -> ()
 ;;
 
 module type For_let_syntax_local =
@@ -10530,3 +10529,11 @@ let _ =
     (* foooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo *)
   else f
 ;;
+
+let _ =
+  match ids_queue with
+  | Some q ->
+    (* this is more efficient than a linear scan of [ids] *)
+    fun id -> not (Ident.HashQueue.mem q id)
+  | None -> fun id -> not (List.mem ~equal:Ident.equal ids id)
+;;

test/passing/tests/js_source.ml.ref

@@ -10235,8 +10235,7 @@ let _ =
     foooooooooooooooooo
     foooooooooooooooooo
     foooooooooooooooooo
-    foooooooooooooooooo ->
-    ()
+    foooooooooooooooooo -> ()
 ;;
 
 module type For_let_syntax_local =
@@ -10530,3 +10529,11 @@ let _ =
     (* foooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo *)
   else f
 ;;
+
+let _ =
+  match ids_queue with
+  | Some q ->
+    (* this is more efficient than a linear scan of [ids] *)
+    fun id -> not (Ident.HashQueue.mem q id)
+  | None -> fun id -> not (List.mem ~equal:Ident.equal ids id)
+;;