Add do/while double definition tests and reoptimize

Author: nicolasstucki

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

@@ -1353,7 +1353,7 @@ object Parsers {
             }
             patch(source, cond.span.endPos, "}) ()")
           }
-          WhileDo(Block(Block(Nil, body), Block(Nil, cond)), Literal(Constant(())))
+          WhileDo(Block(body, cond), Literal(Constant(())))
         }
       case TRY =>
         val tryOffset = in.offset

tests/pos-scala2/doWhile.scala

@@ -0,0 +1,29 @@
+class Test {
+  do {
+    val x = 1
+    println(x)
+  } while {
+    val x = "a"
+    println(x)
+    true
+  }
+
+  do {
+    val x = 1
+  } while {
+    val x = "a"
+    true
+  }
+
+  val x: Int = 3
+  do {
+    val x = ""
+  } while (x == 2)
+
+  do (x == 3)
+  while {
+    val x = "a"
+    true
+  }
+
+}