newline between doc comment and attr on external

Forces a line break following doc comments before the first
non-comment attribute on a BuckleScript external.

Before:

/** doc comment */ [@bs.send] external url : t => string = "";

/**
 * Short multiline doc comment
 */ [@bs.send]
external url : t => string = "";

After:

/** doc comment */
[@bs.send]
external url : t => string = "";

/**
 * Short multiline doc comment
 */
[@bs.send]
external url : t => string = "";

formatTest/typeCheckedTests/expected_output/reasonComments.re

@@ -727,3 +727,20 @@ let r = {
   fieldOne: (identifier: string), /*eol1*/
   fieldTwo: (identifier: string) /* eol2 with trailing comma */
 };
+
+/** doc comment */
+[@bs.send]
+external url : t => string = "";
+
+/**
+ * Short multiline doc comment
+ */
+[@bs.send]
+external url : t => string = "";
+
+/** Longer doc comment before an attribute on an external. */
+[@bs.send]
+external url : t => string = "";
+
+/* normal comment */
+[@bs.send] external url : t => string = "";

formatTest/typeCheckedTests/input/reasonComments.re

@@ -711,3 +711,20 @@ let r = {
   fieldOne: (identifier : string), /*eol1*/
   fieldTwo: (identifier : string), /* eol2 with trailing comma */
 };
+
+/** doc comment */
+[@bs.send]
+external url : t => string = "";
+
+/**
+ * Short multiline doc comment
+ */
+[@bs.send]
+external url : t => string = "";
+
+/** Longer doc comment before an attribute on an external. */
+[@bs.send]
+external url : t => string = "";
+
+/* normal comment */
+[@bs.send] external url : t => string = "";

src/reason-parser/reason_pprint_ast.ml

@@ -317,6 +317,23 @@ let rec partitionAttributes ?(allowUncurry=true) attrs : attributesPartition =
         let partition = partitionAttributes ~allowUncurry atTl in
         {partition with stdAttrs=atHd::partition.stdAttrs}
 
+type docAttributesPartition = {
+  docAttrs : attributes;
+  otherAttrs : attributes
+}
+
+let rec partitionDocAttributes attrs : docAttributesPartition =
+  match attrs with
+    | [] ->
+      {docAttrs=[]; otherAttrs=[]}
+    | (({txt="ocaml.text"; loc}, _) as doc)::atTl
+    | (({txt="ocaml.doc"; loc}, _) as doc)::atTl ->
+        let partition = partitionDocAttributes atTl in
+        {partition with docAttrs=doc::partition.docAttrs}
+    | atHd :: atTl ->
+        let partition = partitionDocAttributes atTl in
+        {partition with otherAttrs=atHd::partition.otherAttrs}
+
 let extractStdAttrs attrs =
   (partitionAttributes attrs).stdAttrs
 
@@ -5315,7 +5332,8 @@ let printer = object(self:'self)
     | _ -> true
 
   (*
-    [@@bs.val] [@@bs.module "react-dom"]                  (* formattedAttrs *)
+    /** doc comment */                                    (* formattedDocs *)
+    [@bs.val] [@bs.module "react-dom"]                    (* formattedAttrs *)
     external render : reactElement => element => unit =   (* frstHalf *)
       "render";                                           (* sndHalf *)
 
@@ -5324,6 +5342,7 @@ let printer = object(self:'self)
       * combine that label with '=' in a list
       * consider the part after the '=' as a list
       * combine both parts as a label
+      * format the doc comment with a ~postSpace:true (inline, not inline) list
       * format the attributes with a ~postSpace:true (inline, inline) list
       * format everything together in a ~postSpace:true (inline, inline) list
         for nicer breaking
@@ -5340,9 +5359,16 @@ let printer = object(self:'self)
     match vd.pval_attributes with
     | [] -> primDecl
     | attrs ->
-        let attrs = List.map (fun x -> self#item_attribute x) attrs in
+        let {docAttrs; otherAttrs} = partitionDocAttributes attrs in
+        let docs = List.map self#item_attribute docAttrs in
+        let formattedDocs = makeList ~postSpace:true docs in
+        let attrs = List.map self#item_attribute otherAttrs in
         let formattedAttrs = makeSpacedBreakableInlineList attrs in
-        makeSpacedBreakableInlineList [formattedAttrs; primDecl]
+        let layouts = match (docAttrs, otherAttrs) with
+        | ([], _) -> [formattedAttrs; primDecl]
+        | (_, []) -> [formattedDocs; primDecl]
+        | _ -> [formattedDocs; formattedAttrs; primDecl] in
+        makeSpacedBreakableInlineList layouts
 
   method class_instance_type x =
     match x.pcty_desc with