Fixed soundness hole in TypeComparer

Two named types with same names and NoPrefix prefixes are not necessarily equal!
The fix uncovered an error in tailrec. When run on Decorators.scala, tailrec in its old
position at the end of a group produces not -Ycheckable code. Problem was fixed
by moving TailRec into its own group.

3 files changed, 12 insertions, 4 deletions

diff --git a/src/dotty/tools/dotc/Compiler.scala b/src/dotty/tools/dotc/Compiler.scala
index 943b54d7f..c5c1d8713 100644
--- a/src/dotty/tools/dotc/Compiler.scala
+++ b/src/dotty/tools/dotc/Compiler.scala
@@ -45,8 +45,10 @@ class Compiler {
       List(new RefChecks,
            new ElimRepeated,
            new ElimLocals,
-           new ExtensionMethods,
-           new TailRec),
+           new ExtensionMethods),
+      List(new TailRec), // TailRec needs to be in its own group for now.
+                         // Otherwise it produces -Ycheck incorrect code for
+                         // file core/Decorators.scala.
       List(new PatternMatcher,
            new ExplicitOuter,
            new Splitter),
diff --git a/src/dotty/tools/dotc/Run.scala b/src/dotty/tools/dotc/Run.scala
index f7d89e897..abee30aab 100644
--- a/src/dotty/tools/dotc/Run.scala
+++ b/src/dotty/tools/dotc/Run.scala
@@ -46,6 +46,7 @@ class Run(comp: Compiler)(implicit ctx: Context) {
         .filterNot(ctx.settings.Yskip.value.containsPhase(_)) // TODO: skip only subphase
       for (phase <- phasesToRun)
         if (!ctx.reporter.hasErrors) {
+          if (ctx.settings.verbose.value) println(s"[$phase]")
           units = phase.runOn(units)
           def foreachUnit(op: Context => Unit)(implicit ctx: Context): Unit =
             for (unit <- units) op(ctx.fresh.setPhase(phase.next).setCompilationUnit(unit))
diff --git a/src/dotty/tools/dotc/core/TypeComparer.scala b/src/dotty/tools/dotc/core/TypeComparer.scala
index faeef559c..720e372d2 100644
--- a/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -167,8 +167,13 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling wi
                      )
                    }
                 )
-              else (tp1.name eq tp2.name) && isSameType(tp1.prefix, tp2.prefix)
-              ) || isHKSubType || secondTryNamed(tp1, tp2)
+              else 
+                (tp1.name eq tp2.name) && 
+                isSameType(tp1.prefix, tp2.prefix) && 
+                (tp1.signature == tp1.signature) &&
+                !tp1.isInstanceOf[WithFixedSym] &&
+                !tp2.isInstanceOf[WithFixedSym]
+           ) || isHKSubType || secondTryNamed(tp1, tp2)
             case tp1: ThisType if tp1.cls eq tp2.symbol.moduleClass =>
               isSubType(tp1.cls.owner.thisType, tp2.prefix)
             case _ =>