Fix output of decompiler when emitting to a file

Author: nicolasstucki

compiler/src/dotty/tools/dotc/decompiler/DecompilationPrinter.scala

@@ -24,7 +24,7 @@ class DecompilationPrinter extends Phase {
       var os: OutputStream = null
       var ps: PrintStream = null
       try {
-        os = File(outputDir + ".decompiled").outputStream()
+        os = File(outputDir + ".decompiled").outputStream(append = true)
         ps = new PrintStream(os)
         printToOutput(ps)
       } finally {

compiler/src/dotty/tools/dotc/decompiler/Main.scala

@@ -1,5 +1,7 @@
 package dotty.tools.dotc.decompiler
 
+import java.nio.file.{Files, Paths}
+
 import dotty.tools.dotc
 import dotty.tools.dotc.core.Contexts._
 
@@ -10,6 +12,9 @@ import dotty.tools.dotc.core.Contexts._
 object Main extends dotc.Driver {
   override protected def newCompiler(implicit ctx: Context): dotc.Compiler = {
     assert(ctx.settings.fromTasty.value)
+    val outputDir = ctx.settings.outputDir.value
+    if (outputDir != ".")
+      Files.deleteIfExists(Paths.get(outputDir + ".decompiled"))
     new TASTYDecompiler
   }