Add configuration to disable newlines between multiline defs

scalafmt-core/shared/src/main/scala/org/scalafmt/config/Newlines.scala

@@ -102,6 +102,22 @@ import metaconfig._
   *     // ...
   *   }
   *   else //...
+  * @param alwaysBeforeMultilineDef
+  *   If true, add a newline before the body of a multiline def without
+  *   curly braces. See #1126 for discussion.
+  *   For example,
+  *   {{{
+  *     // newlines.alwaysBeforeMultilineDef = false
+  *     def foo(bar: Bar): Foo = bar
+  *       .flatMap(f)
+  *       .map(g)
+  *
+  *     // newlines.alwaysBeforeMultilineDef = true
+  *     def foo(bar: Bar): Foo =
+  *       bar
+  *         .flatMap(f)
+  *         .map(g)
+  *   }}}
   */
 @DeriveConfDecoder
 case class Newlines(
@@ -114,7 +130,8 @@ case class Newlines(
     afterCurlyLambda: NewlineCurlyLambda = NewlineCurlyLambda.never,
     afterImplicitKWInVerticalMultiline: Boolean = false,
     beforeImplicitKWInVerticalMultiline: Boolean = false,
-    alwaysBeforeElseAfterCurlyIf: Boolean = false
+    alwaysBeforeElseAfterCurlyIf: Boolean = false,
+    alwaysBeforeMultilineDef: Boolean = true
 )
 
 sealed abstract class NewlineCurlyLambda

scalafmt-core/shared/src/main/scala/org/scalafmt/internal/Router.scala

@@ -403,6 +403,8 @@ class Router(formatOps: FormatOps) {
               //     1
               // )
               true
+            case RightParen() if !style.newlines.alwaysBeforeMultilineDef =>
+              true
             case _ => false
           }
         )
@@ -418,7 +420,10 @@ class Router(formatOps: FormatOps) {
                 Space,
                 0,
                 ignoreIf = newlines > 0 && !rhsIsJsNative,
-                policy = SingleLineBlock(expire, exclude = exclude)),
+                policy =
+                  if (!style.newlines.alwaysBeforeMultilineDef) NoPolicy
+                  else SingleLineBlock(expire, exclude = exclude)
+              ),
               Split(Newline, 1, ignoreIf = rhsIsJsNative)
                 .withIndent(2, expire, Left)
             )

scalafmt-tests/src/test/resources/default/DefDef.stat

@@ -283,3 +283,23 @@ def zip[C](x: A =>? C): A =>? (B, C) = 2
   implicit def adtSyntax[A](target: A): Any =
     LiftMacros.materializeADTSyntax[A]
 }
+<<< #1126 Should format and add newline before multiline def
+def foo = bar.flatMap(x => f(x))
+  .flatMap(y => g(y)).map(z => veryLongFunctionNameFor80Characters(z))
+>>>
+def foo =
+  bar
+    .flatMap(x => f(x))
+    .flatMap(y => g(y))
+    .map(z => veryLongFunctionNameFor80Characters(z))
+<<< #1126
+def foo = Future({
+  val bar = fetchBar()
+  bar.map(_ + 10)
+})
+>>>
+def foo =
+  Future({
+    val bar = fetchBar()
+    bar.map(_ + 10)
+  })

scalafmt-tests/src/test/resources/newlines/alwaysBeforeMultilineDef.stat

@@ -0,0 +1,20 @@
+maxColumn = 40
+newlines.alwaysBeforeMultilineDef = false
+
+<<< Wrap long line but don't add newline
+def foo = bar
+  .flatMap(x => f(x)).map(x => g(x))
+>>>
+def foo = bar
+  .flatMap(x => f(x))
+  .map(x => g(x))
+<<< Don't touch multiline function call
+def foo = Future({
+  val bar = fetchBar()
+  bar.map(_ + 10)
+})
+>>>
+def foo = Future({
+  val bar = fetchBar()
+  bar.map(_ + 10)
+})