Smart linebreak printer for pipe chains

Author: fhammerschmidt

jscomp/syntax/src/res_printer.ml

@@ -3528,7 +3528,7 @@ and printBinaryExpression ~state (expr : Parsetree.expression) cmtTbl =
       [spacingBeforeOperator; Doc.text operatorTxt; spacingAfterOperator]
   in
   let printOperand ~isLhs expr parentOperator =
-    let rec flatten ~isLhs expr parentOperator =
+    let rec flatten ~isLhs ~isMultiLinePipe expr parentOperator =
       if ParsetreeViewer.isBinaryExpression expr then
         match expr with
         | {
@@ -3541,7 +3541,18 @@ and printBinaryExpression ~state (expr : Parsetree.expression) cmtTbl =
             ParsetreeViewer.flattenableOperators parentOperator operator
             && not (ParsetreeViewer.hasAttributes expr.pexp_attributes)
           then
-            let leftPrinted = flatten ~isLhs:true left operator in
+            (* If the pipe-chain is written over multiple lines, break automatically
+             * `let x = a->b->c -> same line, break when line-width exceeded
+             * `let x = a->
+             *   b->c` -> pipe-chain is written on multiple lines, break the group *)
+            let isMultiLinePipe =
+              isMultiLinePipe
+              || left.pexp_loc.loc_start.pos_lnum
+                 < right.pexp_loc.loc_start.pos_lnum
+            in
+            let leftPrinted =
+              flatten ~isLhs:true ~isMultiLinePipe left operator
+            in
             let rightPrinted =
               let rightPrinteableAttrs, rightInternalAttrs =
                 ParsetreeViewer.partitionPrintableAttributes
@@ -3585,12 +3596,22 @@ and printBinaryExpression ~state (expr : Parsetree.expression) cmtTbl =
                     Doc.rparen;
                   ]
               else
-                Doc.concat
-                  [
-                    leftPrinted;
-                    printBinaryOperator ~inlineRhs:false operator;
-                    rightPrinted;
-                  ]
+                match operator with
+                | ("|." | "|.u") when isMultiLinePipe ->
+                  Doc.breakableGroup ~forceBreak:true
+                    (Doc.concat
+                       [
+                         leftPrinted;
+                         printBinaryOperator ~inlineRhs:false operator;
+                         rightPrinted;
+                       ])
+                | _ ->
+                  Doc.concat
+                    [
+                      leftPrinted;
+                      printBinaryOperator ~inlineRhs:false operator;
+                      rightPrinted;
+                    ]
             in
 
             let doc =
@@ -3665,7 +3686,7 @@ and printBinaryExpression ~state (expr : Parsetree.expression) cmtTbl =
           | Braced braces -> printBraces doc expr braces
           | Nothing -> doc)
     in
-    flatten ~isLhs expr parentOperator
+    flatten ~isLhs ~isMultiLinePipe:false expr parentOperator
   in
   match expr.pexp_desc with
   | Pexp_apply

jscomp/syntax/tests/conversion/reason/expected/fastPipe.res.txt

@@ -22,3 +22,16 @@ let aggregateTotal = (forecast, ~audienceType) =>
     views: item["reach"]["views"],
     sample: item["reach"]["sample"],
   })
+
+let myFunc = (strA, strB) => strA ++ strB
+
+"expr1"->myFunc("expr2")->myFunc("expr3")
+
+"expr1"
+->myFunc("expr2")
+->myFunc("expr3")
+
+"expr1"
+->myFunc("expr2")
+->myFunc("expr3")
+->myFunc("expr4")

jscomp/syntax/tests/conversion/reason/fastPipe.res

@@ -22,3 +22,13 @@ let aggregateTotal = (forecast, ~audienceType) =>
     views: item["reach"]["views"],
     sample: item["reach"]["sample"],
   })
+
+let myFunc = (strA, strB) => strA ++ strB
+
+"expr1"->myFunc("expr2")->myFunc("expr3")
+
+"expr1"
+->myFunc("expr2")->myFunc("expr3")
+
+"expr1"->myFunc("expr2")
+->myFunc("expr3")->myFunc("expr4")

jscomp/syntax/tests/printer/expr/expected/callback.res.txt

@@ -215,13 +215,16 @@ let f = () => {
   </div>
 }
 
-myPromise->Js.Promise.then_(value => {
+myPromise
+->Js.Promise.then_(value => {
   Js.log(value)
   Js.Promise.resolve(value + 2)
-}, _)->Js.Promise.then_(value => {
+}, _)
+->Js.Promise.then_(value => {
   Js.log(value)
   Js.Promise.resolve(value + 3)
-}, _)->Js.Promise.catch(err => {
+}, _)
+->Js.Promise.catch(err => {
   Js.log2("Failure!!", err)
   Js.Promise.resolve(-2)
 }, _)