Introduce setFlagFrom

Author: odersky

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -1485,6 +1485,11 @@ object SymDenotations {
     override def transformAfter(phase: DenotTransformer, f: SymDenotation => SymDenotation)(implicit ctx: Context): Unit =
       super.transformAfter(phase, f)
 
+    /** Set flag `flags` in current phase and in all phases that follow */
+    def setFlagFrom(phase: DenotTransformer, flags: FlagSet)(using Context): Unit =
+      setFlag(flags)
+      transformAfter(phase, sd => { sd.setFlag(flags); sd })
+
     /** If denotation is private, remove the Private flag and expand the name if necessary */
     def ensureNotPrivate(implicit ctx: Context): SymDenotation =
       if (is(Private))

compiler/src/dotty/tools/dotc/transform/AugmentScala2Traits.scala

@@ -64,7 +64,6 @@ class AugmentScala2Traits extends MiniPhase with IdentityDenotTransformer { this
         || sym.isSuperAccessor) // scala2 superaccessors are pickled as private, but are compiled as public expanded
         sym.ensureNotPrivate.installAfter(thisPhase)
     }
-    mixin.setFlag(Scala2xPartiallyAugmented)
-    mixin.transformAfter(thisPhase, d => { d.setFlag(Scala2xPartiallyAugmented); d })
+    mixin.setFlagFrom(thisPhase, Scala2xPartiallyAugmented)
   }
 }

compiler/src/dotty/tools/dotc/transform/PostTyper.scala

@@ -118,7 +118,7 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
                   // if you would use parent param-name `a` to implement param-field `b`
                   // overriding field `b` will actually override field `a`, that is wrong!
                   typr.println(i"super alias: ${sym.showLocated}")
-                  sym.setFlag(SuperParamAlias)
+                  sym.setFlagFrom(thisPhase, SuperParamAlias)
           case _ =>
       case _ =>