Don't strip CR from multiline interpolations

Forward port of bug fix from 2.12.

Leaving an interpolated expression would sanitize
an immediately following line separator.

Author: som-snytt

compiler/src/dotty/tools/dotc/parsing/Scanners.scala

@@ -256,6 +256,13 @@ object Scanners {
       case _ => false
     }
 
+    /** Are we in a `${ }` block? such that RBRACE exits back into multiline string. */
+    private def inMultiLineInterpolatedExpression =
+      currentRegion match {
+        case InBraces(_, InString(true, _)) => true
+        case _ => false
+      }
+
     /** read next token and return last offset
      */
     def skipToken(): Offset = {
@@ -806,7 +813,8 @@ object Scanners {
         case ')' =>
           nextChar(); token = RPAREN
         case '}' =>
-          nextChar(); token = RBRACE
+          if (inMultiLineInterpolatedExpression) nextRawChar() else nextChar()
+          token = RBRACE
         case '[' =>
           nextChar(); token = LBRACKET
         case ']' =>

compiler/test/dotty/tools/dotc/parsing/ParserEdgeTest.scala

@@ -0,0 +1,73 @@
+package dotty.tools
+package dotc
+package parsing
+
+import ast.untpd._
+import core.Constants._
+
+import org.junit.Test
+
+class ParserEdgeTest extends ParserTest {
+  //
+  // CR after right brace of interpolated expression was stripped.
+  //
+  @Test def `t9944 respect line separator`: Unit = {
+    // avoid git stripping CR from a test file; also, inlining doesn't demonstrate the behavior.
+    val CR = "\u000D"
+    val NL = "\u000A"
+    val triple = "\"" * 3
+    val text = s"""class C { def g = "X" ; def f = s${triple}123${CR}${NL}$${g}${CR}${NL}456${triple} }"""
+    def isStripped(s: String) = s.contains(NL) && !s.contains(CR)
+
+    // sanity check
+    assert(text.linesIterator.size == 3, s"line count ${text.linesIterator.size}")
+    assert(text.linesIterator.forall(!isStripped(_)))
+
+    val t = parseText(text)
+    //println(t.show)
+    assert(!t.existsSubTree {
+      case Literal(const @ Constant(_)) if const.tag == StringTag => isStripped(const.stringValue)
+      case st => false
+    })
+  }
+  /* was:
+  package <empty> {
+    class C {
+      def g = "X"
+      def f =
+        s"123\r\n{
+          {
+            g
+          }
+        }\n456"
+    }
+  }
+   * now:
+  package <empty> {
+    class C {
+      def g = "X"
+      def f =
+        s"123\r\n{
+          {
+            g
+          }
+        }\r\n456"
+    }
+  }
+   * tests/run/t9944 expressed ordinarily, with CR as indicated:
+class C {
+  def g = 42
+  def f =
+    s"""123^M
+       |${ g }^M
+       |123""".stripMargin
+}
+
+object Test extends App {
+  println(new C().f.getBytes.toList.map(c => f"$c%02x"))
+}
+   * was:
+➜ dotr Test
+List(31, 32, 33, 0d, 0a, 34, 32, 0a, 31, 32, 33)
+   */
+}

compiler/test/dotty/tools/dotc/parsing/ParserTest.scala

@@ -23,9 +23,10 @@ class ParserTest extends DottyTest {
     parsedTrees.clear()
   }
 
-  def parse(file: PlainFile): Tree = {
-    //println("***** parsing " + file)
-    val source = new SourceFile(file, Codec.UTF8)
+  def parse(file: PlainFile): Tree = parseSource(new SourceFile(file, Codec.UTF8))
+
+  private def parseSource(source: SourceFile): Tree = {
+    //println("***** parsing " + source.file)
     val parser = new Parser(source)
     val tree = parser.parse()
     parsed += 1
@@ -41,4 +42,6 @@ class ParserTest extends DottyTest {
     for (d <- dir.dirs)
       parseDir(d.path)
   }
+
+  def parseText(code: String): Tree = parseSource(SourceFile.virtual("<code>", code))
 }