Add SyntheticMethods miniphase

New phase for Synthetic Method generation. Scala 2.x did it in Typer, but
it's cleaner to do it in a separate phase.

2 files changed, 7 insertions, 1 deletions

diff --git a/src/dotty/tools/dotc/core/Definitions.scala b/src/dotty/tools/dotc/core/Definitions.scala
index 123e6e671..82ed3ce1d 100644
--- a/src/dotty/tools/dotc/core/Definitions.scala
+++ b/src/dotty/tools/dotc/core/Definitions.scala
@@ -423,6 +423,8 @@ class Definitions {
 
   lazy val RootImports = List[Symbol](JavaLangPackageVal, ScalaPackageVal, ScalaPredefModule, DottyPredefModule)
 
+  lazy val overriddenBySynthetic = Set[Symbol](Any_equals, Any_hashCode, Any_toString, Product_canEqual)
+
   def isTupleType(tp: Type)(implicit ctx: Context) = {
     val arity = tp.dealias.argInfos.length
     arity <= MaxTupleArity && (tp isRef TupleClass(arity))
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 8ec5c7295..50c729df1 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -1149,7 +1149,11 @@ object Types {
         (lastSymbol eq null) ||
         (lastSymbol.defRunId != sym.defRunId) ||
         (lastSymbol.defRunId == NoRunId) ||
-        (lastSymbol.infoOrCompleter == ErrorType),
+        (lastSymbol.infoOrCompleter == ErrorType ||
+        defn.overriddenBySynthetic.contains(lastSymbol)
+          // for overriddenBySynthetic symbols a TermRef such as SomeCaseClass.this.hashCode
+          // might be rewritten from Object#hashCode to the hashCode generated at SyntheticMethods
+      ),
         s"data race? overwriting symbol of $this / ${this.getClass} / ${lastSymbol.id} / ${sym.id}")
 
     protected def sig: Signature = Signature.NotAMethod