Router: ignore line breaks for blocks

While previously we were trying to keep blocks without line breaks if
that's how they were originally input, now we actively attempt to take a
multi-line representation and fold it into a single line (fold), or take
a single-line representation and unfold it into multiple lines (unfold).

Fixes #271 #1002 #1043

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

@@ -125,6 +125,15 @@ case class Newlines(
       s"newlines: can't use source=${source} and afterCurlyLambda=$afterCurlyLambda"
     )
   }
+
+  @inline
+  def sourceIs(hint: Newlines.SourceHints): Boolean =
+    hint eq source
+
+  @inline
+  def sourceIn(hints: Newlines.SourceHints*): Boolean =
+    hints.contains(source)
+
 }
 
 object Newlines {

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

@@ -1,7 +1,7 @@
 package org.scalafmt.internal
 
 import org.scalafmt.Error.UnexpectedTree
-import org.scalafmt.config.{ImportSelectors, NewlineCurlyLambda}
+import org.scalafmt.config.{ImportSelectors, NewlineCurlyLambda, Newlines}
 import org.scalafmt.internal.ExpiresOn.{Left, Right}
 import org.scalafmt.internal.Length.{Num, StateColumn}
 import org.scalafmt.internal.Policy.NoPolicy
@@ -250,14 +250,28 @@ class Router(formatOps: FormatOps) {
           else
             getSingleLineDecisionPre2019NovOpt
 
+        def getSingleLineLambdaDecisionOpt = {
+          val ok = !style.newlines.alwaysBeforeCurlyBraceLambdaParams &&
+            getSpaceAndNewlineAfterCurlyLambda(newlines)._1
+          if (ok) Some(getSingleLineDecisionFor2019Nov) else None
+        }
+
         // null if skipping
-        val singleLineDecisionOpt =
-          if (lambdaPolicy == null) getClassicSingleLineDecisionOpt
-          else if (style.activeForEdition_2020_01 &&
-            !style.newlines.alwaysBeforeCurlyBraceLambdaParams &&
-            getSpaceAndNewlineAfterCurlyLambda(newlines)._1)
-            Some(getSingleLineDecisionFor2019Nov)
-          else None
+        val singleLineDecisionOpt = style.newlines.source match {
+          case Newlines.keep if newlines != 0 => None
+          case Newlines.unfold => None
+          case Newlines.fold =>
+            // do not fold top-level blocks
+            if (leftOwner.parent.exists(_.parent.isEmpty) ||
+              leftOwner.is[Template]) None
+            else if (lambdaPolicy != null) getSingleLineLambdaDecisionOpt
+            else Some(getSingleLineDecisionFor2019Nov)
+          // old behaviour
+          case _ =>
+            if (lambdaPolicy == null) getClassicSingleLineDecisionOpt
+            else if (!style.activeForEdition_2020_01) None
+            else getSingleLineLambdaDecisionOpt
+        }
 
         val singleLineSplit =
           singleLineDecisionOpt.fold(Split.ignored) { sld =>
@@ -275,7 +289,8 @@ class Router(formatOps: FormatOps) {
           Split(Space, 0)
             .notIf(
               style.newlines.alwaysBeforeCurlyBraceLambdaParams ||
-                isSelfAnnotation || lambdaPolicy == null
+                isSelfAnnotation || lambdaPolicy == null ||
+                style.newlines.sourceIs(Newlines.keep) && newlines != 0
             )
             .withOptimalTokenOpt(lambdaArrow)
             .withIndent(lambdaIndent, close, Right)

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

@@ -14,9 +14,8 @@ println("bbb") } else c
 }
 >>>
 object a {
-  if (a) {
-    println("bbb")
-  } else c
+  if (a) { println("bbb") }
+  else c
 }
 <<< 1.3: block, if, non-egyptian curlies
 object a {
@@ -30,11 +29,8 @@ c
 }}
 >>>
 object a {
-  if (a) {
-    println("bbb")
-  } else {
-    c
-  }
+  if (a) { println("bbb") }
+  else { c }
 }
 <<< 1.4: block #1043
 object a {
@@ -51,9 +47,7 @@ object a {
     c - 'A' + 10
   } else if ('a' <= c && c <= 'f') {
     c - 'a' + 10
-  } else {
-    -1
-  }
+  } else { -1 }
 }
 <<< 1.5: block #1043 with lines joined
 object a {
@@ -68,9 +62,7 @@ object a {
     c - 'A' + 10
   } else if ('a' <= c && c <= 'f') {
     c - 'a' + 10
-  } else {
-    -1
-  }
+  } else { -1 }
 }
 <<< 1.6: block, try-catch, line too long
 object a {
@@ -101,13 +93,9 @@ try {
 }
 >>>
 object a {
-  try {
-    a
-  } catch {
-    case b => ; case c =>
-  } finally {
-    d
-  }
+  try { a }
+  catch { case b => ; case c => }
+  finally { d }
 }
 <<< 1.9: block, try-catch, with breaks, top-level
 try {
@@ -117,9 +105,8 @@ try {
 >>>
 try {
   a
-} catch {
-  case b => ; case c =>
-} finally {
+} catch { case b => ; case c => }
+finally {
   d
 }
 <<< 1.a: block, class

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

@@ -46,8 +46,9 @@ object a {
        -1  }}
 >>>
 object a {
-  if ('0' <= c && c <= '9') { c - '0' }
-  else if ('A' <= c && c <= 'F') {
+  if ('0' <= c && c <= '9') {
+    c - '0'
+  } else if ('A' <= c && c <= 'F') {
     c - 'A' + 10
   } else if ('a' <= c && c <= 'f') {
     c - 'a' + 10
@@ -63,8 +64,9 @@ object a {
 }}
 >>>
 object a {
-  if ('0' <= c && c <= '9') { c - '0' }
-  else if ('A' <= c && c <= 'F') {
+  if ('0' <= c && c <= '9') {
+    c - '0'
+  } else if ('A' <= c && c <= 'F') {
     c - 'A' + 10
   } else if ('a' <= c && c <= 'f') {
     c - 'a' + 10
@@ -80,17 +82,23 @@ try { aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa } catch { case b => }
 object a {
   try {
     aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
-  } catch { case b => }
+  } catch {
+    case b =>
+  }
 }
 <<< 1.7: block, try-catch, no breaks
 object a {
 try { a } catch { case b => ; case c => } finally { d }
 }
 >>>
 object a {
-  try { a }
-  catch { case b => ; case c => }
-  finally { d }
+  try {
+    a
+  } catch {
+    case b => ; case c =>
+  } finally {
+    d
+  }
 }
 <<< 1.8: block, try-catch, with breaks
 object a {
@@ -149,7 +157,9 @@ object a {
     type c = Int
   }
   object b {
-    def apply(c: Int) = { new d(c) }
+    def apply(c: Int) = {
+      new d(c)
+    }
   }
 }
 <<< 1.c: block followed by an infix, overflowing if no break