Implement intelligent breaking for poly-var type expressions

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## Unreleased
 
+* Implement intelligent breaking for poly-var type expressions in [#246](https://github.com/rescript-lang/syntax/pull/246)
 * Improve indentation of fast pipe chain in let binding in [#244](https://github.com/rescript-lang/syntax/pull/244)
 * Improve printing of non-callback arguments in call expressions with callback in [#241](https://github.com/rescript-lang/syntax/pull/241/files)
 * Fix printing of constrained expressions in rhs of js objects [#240](https://github.com/rescript-lang/syntax/pull/240)

src/res_printer.ml

@@ -1587,6 +1587,7 @@ and printTypExpr (typExpr : Parsetree.core_type) cmtTbl =
   | Ptyp_class _ ->
     Doc.text "classes are not supported in types"
   | Ptyp_variant (rowFields, closedFlag, labelsOpt) ->
+    let forceBreak = typExpr.ptyp_loc.Location.loc_start.pos_lnum < typExpr.ptyp_loc.loc_end.pos_lnum in
     let printRowField = function
     | Parsetree.Rtag ({txt}, attrs, true, []) ->
       Doc.group (
@@ -1615,7 +1616,10 @@ and printTypExpr (typExpr : Parsetree.core_type) cmtTbl =
     in
     let docs = List.map printRowField rowFields in
     let cases = Doc.join ~sep:(Doc.concat [Doc.line; Doc.text "| "]) docs in
-    let cases = if docs = [] then cases else Doc.concat [Doc.ifBreaks (Doc.text "| ") Doc.nil; cases] in
+    let cases =
+      if docs = [] then cases
+      else Doc.concat [Doc.ifBreaks (Doc.text "| ") Doc.nil; cases]
+    in
     let openingSymbol =
       if closedFlag = Open
       then Doc.concat [Doc.greaterThan; Doc.line]
@@ -1628,10 +1632,14 @@ and printTypExpr (typExpr : Parsetree.core_type) cmtTbl =
     | Some([]) ->
       Doc.nil
     | Some(labels) ->
-      Doc.concat (List.map (fun label -> Doc.concat [Doc.line; Doc.text "#" ; printPolyVarIdent label] ) labels)
+      Doc.concat (
+        List.map (fun label ->
+          Doc.concat [Doc.line; Doc.text "#" ; printPolyVarIdent label]
+        ) labels
+      )
     in
     let closingSymbol = if hasLabels then Doc.text " >" else Doc.nil in
-    Doc.group (
+    Doc.breakableGroup ~forceBreak (
       Doc.concat [
         Doc.lbracket;
         Doc.indent (

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

@@ -596,7 +596,10 @@ let id = (x: [> #Red | #Green | #Blue]) => x
 let upper = (x: [< #Red | #Green]) => true
 type point = [#Point(float, float)]
 type \\\\\\"type\\" = [#\\"Point🗿\\"(\\\\\\"let\\", float)]
-type shape = [#Rectangle(point, point) | #Circle(point, float)]
+type shape = [
+  | #Rectangle(point, point)
+  | #Circle(point, float)
+]
 
 type madness = [< #\\"type\\" & (\\\\\\"let\\") & (\\\\\\"Super exotic\\") | #\\"Bad Idea\\"]
 
@@ -648,7 +651,11 @@ type x = [
   | #Baaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaz
 ]
 
-type animation = [#\\"ease-in\\" | #\\"ease-out\\" | #\\"never ease ✍️\\"]
+type animation = [
+  | #\\"ease-in\\"
+  | #\\"ease-out\\"
+  | #\\"never ease ✍️\\"
+]
 
 module type Conjunctive = {
   type u1 = [#A | #B]
@@ -663,5 +670,22 @@ module type Conjunctive = {
     & ([< #\\"Exotic-u1+++\\"])
   ] => unit
 }
+
+// should break because user wrote it over serveral lines
+type currencyPoly = [
+  | #USD
+  | #CAD
+  | #EUR
+]
+
+// should not break, user wrote it on one line
+type currencyPoly = [#USD | #CAD | #EUR]
+//
+// should break, line length exceeded
+type currencyPoly = [
+  | #UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUSD
+  | #CAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAD
+  | #EUUUUUUUUUUUUUUUUUUUR
+]
 "
 `;

tests/printer/typexpr/variant.js

@@ -82,3 +82,14 @@ module type Conjunctive = {
   let g: [< | #S&([< u2]) & ([< u2]) & ([< u1])] => unit
   let g: [< | #"Exotic-S+"&([< #"Exotic-u2+"]) & ([< #"Exotic-u2-"]) & ([< #"Exotic-u1+++"])] => unit
 };
+
+
+// should break because user wrote it over serveral lines
+type currencyPoly = [#USD 
+  | #CAD | #EUR]
+
+// should not break, user wrote it on one line
+type currencyPoly = [#USD | #CAD | #EUR]
+//
+// should break, line length exceeded
+type currencyPoly = [#UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUSD | #CAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAD | #EUUUUUUUUUUUUUUUUUUUR]