Clutch modification to tree printing.

Don't print trees under -Xprint:all if they're identical to the
tree printed at the previous phase.  It only works for a single
compilation unit but that is a huge step forward for us debuggers.
For instance this file:

  trait Foo { def f = 5 }

used to produce 332 lines of output and now produces 92, with
zero loss of information.  It ends with:

  [[syntax trees at end of                   cleanup]] // a.scala: tree is unchanged since mixin
  [[syntax trees at end of                     icode]] // a.scala: tree is unchanged since mixin
  [[syntax trees at end of                   inliner]] // a.scala: tree is unchanged since mixin
  [[syntax trees at end of   inlineExceptionHandlers]] // a.scala: tree is unchanged since mixin
  [[syntax trees at end of                  closelim]] // a.scala: tree is unchanged since mixin
  [[syntax trees at end of                       dce]] // a.scala: tree is unchanged since mixin
  [[syntax trees at end of                       jvm]] // a.scala: tree is unchanged since mixin

1 files changed, 25 insertions, 2 deletions

diff --git a/src/compiler/scala/tools/nsc/Global.scala b/src/compiler/scala/tools/nsc/Global.scala
index de270a76f1..49a644ba3a 100644
--- a/src/compiler/scala/tools/nsc/Global.scala
+++ b/src/compiler/scala/tools/nsc/Global.scala
@@ -130,7 +130,28 @@ class Global(var currentSettings: Settings, var reporter: Reporter) extends Symb
   object nodePrinters extends {
     val global: Global.this.type = Global.this
   } with NodePrinters {
+    var lastPrintedPhase: Phase = NoPhase
+    var lastPrintedSource: String = ""
     infolevel = InfoLevel.Verbose
+
+    def showUnit(unit: CompilationUnit) {
+      print(" // " + unit.source)
+      if (unit.body == null) println(": tree is null")
+      else {
+        val source = util.stringFromWriter(w => newTreePrinter(w) print unit.body)
+
+        // treePrinter show unit.body
+        if (lastPrintedSource == source)
+          println(": tree is unchanged since " + lastPrintedPhase)
+        else {
+          lastPrintedPhase = phase.prev // since we're running inside "afterPhase"
+          lastPrintedSource = source
+          println("")
+          println(source)
+          println("")
+        }
+      }
+    }
   }
 
   def withInfoLevel[T](infolevel: nodePrinters.InfoLevel.Value)(op: => T) = {
@@ -1588,8 +1609,10 @@ class Global(var currentSettings: Settings, var reporter: Reporter) extends Symb
   } // class Run
 
   def printAllUnits() {
-    print("[[syntax trees at end of " + phase + "]]")
-    afterPhase(phase) { currentRun.units foreach (treePrinter.print(_)) }
+    print("[[syntax trees at end of %25s]]".format(phase))
+    afterPhase(phase)(currentRun.units foreach { unit =>
+      nodePrinters showUnit unit
+    })
   }
 
   /** We resolve the class/object ambiguity by passing a type/term name.