Fix printing of trailing comments under lhs of "pipe" expression.

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## Unreleased
 
+* Improve printing of trailing comments under lhs of "pipe" expression in [#329](https://github.com/rescript-lang/syntax/pull/239/files)
 * Improve printing of jsx children and props with leading line comment in [#236](https://github.com/rescript-lang/syntax/pull/236)
 * Improve conversion of quoted strings from Reason in [#238](https://github.com/rescript-lang/syntax/pull/238)
 * Print attributes/extension without bs prefix where possible in [#230](https://github.com/rescript-lang/syntax/pull/230)

src/res_printer.ml

@@ -58,6 +58,14 @@ let hasLeadingLineComment tbl loc =
   | Some comment -> Comment.isSingleLineComment comment
   | None -> false
 
+let hasCommentBelow tbl loc =
+  match Hashtbl.find tbl.CommentTable.trailing loc with
+  | comment::_ ->
+    let commentLoc = Comment.loc comment in
+    commentLoc.Location.loc_start.pos_lnum > loc.Location.loc_end.pos_lnum
+  | [] -> false
+  | exception Not_found -> false
+
 let printMultilineCommentContent txt =
   (* Turns
    *         |* first line
@@ -3460,15 +3468,19 @@ and printBinaryExpression (expr : Parsetree.expression) cmtTbl =
         ParsetreeViewer.isBinaryExpression lhs ||
         ParsetreeViewer.isBinaryExpression rhs
     ) ->
+    let lhsHasCommentBelow = hasCommentBelow cmtTbl lhs.pexp_loc in
     let lhsDoc = printOperand ~isLhs:true lhs op in
     let rhsDoc = printOperand ~isLhs:false rhs op in
     Doc.group (
       Doc.concat [
         lhsDoc;
-        (match op with
-        | "|." -> Doc.text "->"
-        | "|>" -> Doc.text " |> "
-        | _ -> assert false);
+        (match lhsHasCommentBelow, op with
+        | true, "|." -> Doc.concat [Doc.softLine; Doc.text "->"]
+        | false, "|." -> Doc.text "->"
+        | true, "|>" -> Doc.concat [Doc.line; Doc.text "|> "]
+        | false, "|>" -> Doc.text " |> "
+        | _ -> Doc.nil
+        );
         rhsDoc;
       ]
     )

tests/printer/comments/__snapshots__/render.spec.js.snap

@@ -37,6 +37,64 @@ let truth =
   /* c0 */ a /* c1 */ == /* c2 */ b /* c3 */ &&
   /* c4 */ c /* c5 */ == /* c6 */ d /* c7 */ &&
   /* c8 */ e /* c9 */ == /* c10 */ f /* c11 */
+
+promise
+// TODO: This comment needs to be here
+->Js.Promise.then(payload => {
+  Js.log2(\\"this payload was received\\", payload)
+  Js.Promise.resolve(\\"\\"->Obj.magic)
+})
+
+promise
+/* TODO: This comment needs to be here */
+->Js.Promise.then(payload => {
+  Js.log2(\\"this payload was received\\", payload)
+  Js.Promise.resolve(\\"\\"->Obj.magic)
+})
+
+promise
+// comment
+->Js.Promise.then(payload => {
+  Js.Promise.resolve(\\"\\"->Obj.magic)
+})
+// comment 2
+->Js.Promise.catch(err => {
+  Js.log2(\\"this error was caught\\", err)
+  Js.Promise.resolve(\\"\\"->Obj.magic)
+})
+
+promise
+/* comment */
+->Js.Promise.then(payload => {
+  Js.Promise.resolve(\\"\\"->Obj.magic)
+})
+/* comment 2 */
+
+// comment 3
+
+/* comment 4 */
+->Js.Promise.catch(err => {
+  Js.log2(\\"this error was caught\\", err)
+  Js.Promise.resolve(\\"\\"->Obj.magic)
+})
+
+promise
+// TODO: This comment needs to be here
+|> Js.Promise.then(payload => {
+  Js.log2(\\"this payload was received\\", payload)
+  Js.Promise.resolve(\\"\\"->Obj.magic)
+})
+
+promise
+// comment
+|> Js.Promise.then(payload => {
+  Js.Promise.resolve(\\"\\"->Obj.magic)
+})
+// comment 2
+|> Js.Promise.catch(err => {
+  Js.log2(\\"this error was caught\\", err)
+  Js.Promise.resolve(\\"\\"->Obj.magic)
+})
 "
 `;
 

tests/printer/comments/binaryExpr.res

@@ -34,3 +34,63 @@ let truth =
   /* c0 */ a /* c1 */ == /* c2 */ b /* c3 */ &&
  /* c4 */ c /* c5 */ == /* c6 */ d /* c7 */ &&
   /* c8 */ e /* c9 */ ==  /* c10 */ f  /* c11 */
+
+promise
+// TODO: This comment needs to be here
+->Js.Promise.then(payload => {
+  Js.log2("this payload was received", payload);
+  Js.Promise.resolve(""->Obj.magic);
+})
+
+
+promise
+/* TODO: This comment needs to be here */
+->Js.Promise.then(payload => {
+  Js.log2("this payload was received", payload);
+  Js.Promise.resolve(""->Obj.magic);
+})
+
+promise
+// comment
+->Js.Promise.then(payload => {
+  Js.Promise.resolve(""->Obj.magic);
+})
+// comment 2
+->Js.Promise.catch(err => {
+  Js.log2("this error was caught", err);
+  Js.Promise.resolve(""->Obj.magic);
+})
+
+
+promise
+/* comment */
+->Js.Promise.then(payload => {
+  Js.Promise.resolve(""->Obj.magic);
+})
+/* comment 2 */
+
+// comment 3
+
+/* comment 4 */
+->Js.Promise.catch(err => {
+  Js.log2("this error was caught", err);
+  Js.Promise.resolve(""->Obj.magic);
+})
+
+promise
+// TODO: This comment needs to be here
+|> Js.Promise.then(payload => {
+  Js.log2("this payload was received", payload);
+  Js.Promise.resolve(""->Obj.magic);
+})
+
+promise
+// comment
+|> Js.Promise.then(payload => {
+  Js.Promise.resolve(""->Obj.magic);
+})
+// comment 2
+|> Js.Promise.catch(err => {
+  Js.log2("this error was caught", err);
+  Js.Promise.resolve(""->Obj.magic);
+})