Add parents when it's a JSX expression

lib/Fmt_ast.ml

@@ -2273,6 +2273,11 @@ and fmt_expression c ?(box = true) ?(pro = noop) ?eol ?parens
   | Pexp_apply (e0, e1N1) -> (
       match pexp_attributes with
       | [{attr_name={txt="JSX";loc=_}; attr_payload=PStr []; _}] ->
+        let is_jsx_element e =
+          match e.pexp_attributes with
+          | [{attr_name={txt="JSX";_}; attr_payload=PStr []; _}] -> true
+          | _ -> false
+        in
         let children = ref None in
         let props = List.filter_map e1N1 ~f:(function
           | Labelled {txt="children";_}, {pexp_desc=Pexp_list es;pexp_loc;_} ->
@@ -2311,7 +2316,10 @@ and fmt_expression c ?(box = true) ?(pro = noop) ?eol ?parens
               | Pexp_ident {txt=Lident id; loc=_} when String.equal id label.txt ->
                 flabel
               | _ ->
-                flabel $ str "=" $ fmt_expression c (sub_exp ~ctx e)
+                if is_jsx_element e then
+                  flabel $ str "=" $ fmt_expression c ~parens:true (sub_exp ~ctx e)
+                else
+                  flabel $ str "=" $ fmt_expression c (sub_exp ~ctx e)
             in
             let fmt_prop = function
               | Nolabel, e -> fmt_expression c (sub_exp ~ctx e)
@@ -2320,20 +2328,25 @@ and fmt_expression c ?(box = true) ?(pro = noop) ?eol ?parens
             in
             space_break $ hvbox 0 (list props (break 1 0) fmt_prop)
         in
-        begin match !children with
-        | None -> hvbox 2 (start_tag () $ props) $ space_break $ str "/>"
-        | Some (children_loc, []) when not (Cmts.has_after c.cmts children_loc) ->
-          hvbox 2 (start_tag () $ props) $ space_break $ str "/>"
-        | Some (children_loc, children) ->
-          let head = hvbox 2 (start_tag () $ props $ str ">") in
-          let children =
-            hvbox 0 (
-              list children (break 1 0)
-              (fun e -> fmt_expression c (sub_exp ~ctx e))
-              $ Cmts.fmt_after c children_loc)
-          in
-          hvbox 2 (head $ break 0 0 $ children $ break 0 (-2) $ end_tag ())
-        end
+        Params.parens_if parens c.conf (
+          match !children with
+          | None -> hvbox 2 (start_tag () $ props) $ space_break $ str "/>"
+          | Some (children_loc, []) when not (Cmts.has_after c.cmts children_loc) ->
+            hvbox 2 (start_tag () $ props) $ space_break $ str "/>"
+          | Some (children_loc, children) ->
+            let head = hvbox 2 (start_tag () $ props $ str ">") in
+            let children =
+              hvbox 0 (
+                list children (break 1 0)
+                (fun e ->
+                  if is_jsx_element e then
+                    fmt_expression c ~parens:false (sub_exp ~ctx e)
+                  else
+                    fmt_expression c (sub_exp ~ctx e))
+                $ Cmts.fmt_after c children_loc)
+            in
+            hvbox 2 (head $ break 0 0 $ children $ break 0 (-2) $ end_tag ())
+        )
       | _ ->
       let wrap =
         if c.conf.fmt_opts.wrap_fun_args.v then hovbox 2 else hvbox 2

test/mlx/mlx.t

@@ -172,3 +172,23 @@ Test for a lexer hack:
   [ <element>1</element> ]
   $ echo '[<M.element> 1 </M.element>]' | fmt
   [ <M.element>1</M.element> ]
+
+JSX elements as props:
+  $ echo 'let _ = <div element=(<span />) />' | fmt
+  let _ = <div element=(<span />) />
+  $ echo 'let _ = <div element=(<Componient />) />' | fmt
+  let _ = <div element=(<Componient />) />
+  $ echo 'let _ = <Big element=(<Component />) />' | fmt
+  let _ = <Big element=(<Component />) />
+
+  $ echo 'let _ = <Big>(<Component />)</Big>' | fmt
+  let _ = <Big><Component /></Big>
+
+  $ echo 'let _ = <Big>(React.string children)</Big>' | fmt
+  let _ = <Big>(React.string children)</Big>
+
+  $ echo 'let _ = <Big>(match x with | A -> "33" | B -> "44")</Big>' | fmt
+  let _ = <Big>(match x with A -> "33" | B -> "44")</Big>
+
+  $ echo 'let _ = <Big>(<Lola />)</Big>' | fmt
+  let _ = <Big><Lola /></Big>