Fixed data race in ResolveSuper

The datarace happened because for method "transform" implemented
by ResolveSuper which disambiguated overridden methods.
Previously, there was a reference FirstTransform.this.transform
of type termRefWithSig to the method implemented in a super trait. Now the same
reference points to the newly implemented method.

Solved because ResolveSuper now generates symbolic references.

Author: odersky

src/dotty/tools/dotc/core/Phases.scala

@@ -220,6 +220,7 @@ object Phases {
     private var myErasedTypes = false
     private var myFlatClasses = false
     private var myRefChecked = false
+    private var mySymbolicRefs = false
 
     /** The sequence position of this phase in the given context where 0
      * is reserved for NoPhase and the first real phase is at position 1.
@@ -231,18 +232,20 @@ object Phases {
     def start = myPeriod.firstPhaseId
     def end = myPeriod.lastPhaseId
 
-    final def erasedTypes = myErasedTypes
-    final def flatClasses = myFlatClasses
-    final def refChecked = myRefChecked
+    final def erasedTypes = myErasedTypes   // Phase is after erasure
+    final def flatClasses = myFlatClasses   // Phase is after flatten
+    final def refChecked = myRefChecked     // Phase is after RefChecks
+    final def symbolicRefs = mySymbolicRefs // Phase is after ResolveSuper, newly generated TermRefs should be symbolic
 
     protected[Phases] def init(base: ContextBase, start: Int, end:Int): Unit = {
       if (start >= FirstPhaseId)
         assert(myPeriod == Periods.InvalidPeriod, s"phase $this has already been used once; cannot be reused")
       myBase = base
       myPeriod = Period(start, end)
-      myErasedTypes = prev.getClass == classOf[Erasure]   || prev.erasedTypes
-      myFlatClasses = prev.getClass == classOf[Flatten]   || prev.flatClasses
-      myRefChecked  = prev.getClass == classOf[RefChecks] || prev.refChecked
+      myErasedTypes  = prev.getClass == classOf[Erasure]      || prev.erasedTypes
+      myFlatClasses  = prev.getClass == classOf[Flatten]      || prev.flatClasses
+      myRefChecked   = prev.getClass == classOf[RefChecks]    || prev.refChecked
+      mySymbolicRefs = prev.getClass == classOf[ResolveSuper] || prev.symbolicRefs
     }
 
     protected[Phases] def init(base: ContextBase, id: Int): Unit = init(base, id, id)

src/dotty/tools/dotc/core/Types.scala

@@ -1526,6 +1526,8 @@ object Types {
 
   object TermRef {
 
+    private def symbolicRefs(implicit ctx: Context) = ctx.phase.symbolicRefs
+
     /** Create term ref with given name, without specifying a signature.
      *  Its meaning is the (potentially multi-) denotation of the member(s)
      *  of prefix with given name.
@@ -1546,7 +1548,7 @@ object Types {
      *  signature, if denotation is not yet completed.
      */
     def apply(prefix: Type, name: TermName, denot: Denotation)(implicit ctx: Context): TermRef = {
-      if ((prefix eq NoPrefix) || denot.symbol.isFresh || ctx.erasedTypes)
+      if ((prefix eq NoPrefix) || denot.symbol.isFresh || symbolicRefs)
         apply(prefix, denot.symbol.asTerm)
       else denot match {
         case denot: SymDenotation if denot.isCompleted => withSig(prefix, name, denot.signature)
@@ -1568,7 +1570,7 @@ object Types {
      *  (2) The name in the term ref need not be the same as the name of the Symbol.
      */
     def withSymAndName(prefix: Type, sym: TermSymbol, name: TermName)(implicit ctx: Context): TermRef =
-      if ((prefix eq NoPrefix) || sym.isFresh || ctx.erasedTypes)
+      if ((prefix eq NoPrefix) || sym.isFresh || symbolicRefs)
         withFixedSym(prefix, name, sym)
       else if (sym.defRunId != NoRunId && sym.isCompleted)
         withSig(prefix, name, sym.signature) withSym (sym, sym.signature)
@@ -1579,7 +1581,7 @@ object Types {
      *  (which must be completed).
      */
     def withSig(prefix: Type, sym: TermSymbol)(implicit ctx: Context): TermRef =
-      if ((prefix eq NoPrefix) || sym.isFresh || ctx.erasedTypes) withFixedSym(prefix, sym.name, sym)
+      if ((prefix eq NoPrefix) || sym.isFresh || symbolicRefs) withFixedSym(prefix, sym.name, sym)
       else withSig(prefix, sym.name, sym.signature).withSym(sym, sym.signature)
 
     /** Create a term ref with given prefix, name and signature */
@@ -1588,7 +1590,7 @@ object Types {
 
     /** Create a term ref with given prefix, name, signature, and initial denotation */
     def withSigAndDenot(prefix: Type, name: TermName, sig: Signature, denot: Denotation)(implicit ctx: Context): TermRef = {
-      if ((prefix eq NoPrefix) || denot.symbol.isFresh || ctx.erasedTypes)
+      if ((prefix eq NoPrefix) || denot.symbol.isFresh || symbolicRefs)
         withFixedSym(prefix, denot.symbol.asTerm.name, denot.symbol.asTerm)
       else
         withSig(prefix, name, sig)

test/dotc/tests.scala

@@ -113,8 +113,7 @@ class tests extends CompilerTest {
   @Test def dotc_config = compileDir(dotcDir + "tools/dotc/config", twice)
   @Test def dotc_core = compileDir(dotcDir + "tools/dotc/core", twice)(allowDeepSubtypes)
   @Test def dotc_core_pickling = compileDir(dotcDir + "tools/dotc/core/pickling", twice)(allowDeepSubtypes)
-  // @Test def dotc_transform = compileDir(dotcDir + "tools/dotc/transform", twice)
-  // @odersky causes race error in ResolveSuper
+  @Test def dotc_transform = compileDir(dotcDir + "tools/dotc/transform", twice)
 
   @Test def dotc_parsing = compileDir(dotcDir + "tools/dotc/parsing", twice)
   @Test def dotc_printing = compileDir(dotcDir + "tools/dotc/printing", twice)