solve issue

Author: EmileTrotignon

lib/Fmt_ast.ml

@@ -3803,6 +3803,13 @@ and fmt_module_type c ?(rec_ = false) ({ast= mty; _} as xmty) =
         bdy= fmt_longident_loc c lid
       ; epi= Some (fmt_attributes c pmty_attributes ~pre:(Break (1, 0))) }
   | Pmty_signature s ->
+      let is_signature_multiline =
+        match s with
+        | [] -> false
+        | _ :: _ ->
+            (List.hd_exn s).psig_loc.loc_start.pos_lnum
+            <> (List.last_exn s).psig_loc.loc_start.pos_lnum
+      in
       let empty = List.is_empty s && not (Cmts.has_within c.cmts pmty_loc) in
       let before = Cmts.fmt_before c pmty_loc in
       let within = Cmts.fmt_within c ~pro:noop pmty_loc in
@@ -3817,7 +3824,8 @@ and fmt_module_type c ?(rec_ = false) ({ast= mty; _} as xmty) =
       ; cls= noop
       ; esp=
           fmt_if (not empty)
-            ( if c.conf.fmt_opts.break_struct.v then force_break
+            ( if c.conf.fmt_opts.break_struct.v || is_signature_multiline then
+                force_break
               else break 1 0 )
       ; epi=
           Some

test/passing/refs.ahrefs/break_struct.ml.ref

@@ -94,18 +94,21 @@ module type Module_type_fail = sig
 
   module F : functor (_ : T) -> sig end
 
-  include S end
+  include S
+end
 
 module A : sig
   type a
 
-  type b end =
+  type b
+end =
   B
 
 module A : sig
   type a
 
-  type b end = struct
+  type b
+end = struct
   type a
 
   type b

test/passing/refs.ocamlformat/break_struct.ml.ref

@@ -109,18 +109,21 @@ module type Module_type_fail = sig
 
   module F : functor (_ : T) -> sig end
 
-  include S end
+  include S
+end
 
 module A : sig
   type a
 
-  type b end =
+  type b
+end =
   B
 
 module A : sig
   type a
 
-  type b end = struct
+  type b
+end = struct
   type a
 
   type b