Address review comments

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -1017,7 +1017,7 @@ object desugar {
       var tested: MemberDef = tree
       def fail(msg: String) = ctx.error(msg, tree.sourcePos)
       def checkApplicable(flag: FlagSet, test: MemberDefTest): Unit =
-        if (tested.mods.is(flag) && !(test.isDefinedAt(tree) && test(tree))) {
+        if (tested.mods.is(flag) && !test.applyOrElse(tree, _ => false)) {
           fail(i"modifier `$flag` is not allowed for this definition")
           tested = tested.withMods(tested.mods.withoutFlags(flag))
         }

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

@@ -575,7 +575,7 @@ object SymDenotations {
     /** Is this symbol a user-defined opaque alias type? */
     def isOpaqueAlias(implicit ctx: Context): Boolean = is(Opaque) && !isClass
 
-    /** Is this symbol a module that contains of an opaque aliases? */
+    /** Is this symbol a module that contains opaque aliases? */
     def containsOpaques(implicit ctx: Context): Boolean = is(Opaque) && isClass
 
     def seesOpaques(implicit ctx: Context): Boolean =

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

@@ -1094,15 +1094,15 @@ class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] w
    *  but in this case the retries in tryLiftedToThis would be redundant.
    */
   private def liftToThis(tp: Type): Type = {
-  
+
     def findEnclosingThis(moduleClass: Symbol, from: Symbol): Type =
       if ((from.owner eq moduleClass) && from.isPackageObject && from.is(Opaque)) from.thisType
       else if (from.is(Package)) tp
       else if ((from eq moduleClass) && from.is(Opaque)) from.thisType
       else if (from eq NoSymbol) tp
       else findEnclosingThis(moduleClass, from.owner)
-      
-    tp.stripTypeVar.stripAnnots match {
+
+    tp match {
       case tp: TermRef if tp.symbol.is(Module) =>
         findEnclosingThis(tp.symbol.moduleClass, ctx.owner)
       case tp: TypeRef =>

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

@@ -47,8 +47,8 @@ class ElimOpaque extends MiniPhase with DenotTransformer {
           info = cinfo.derivedClassInfo(selfInfo = strippedSelfType),
           initFlags = ref.flags &~ Opaque)
       case _ =>
-        // This is dubbious as it means that we do not see the alias from an external reference
-        // which has tupe UniqueRefDenotion instead of SymDenotation. But to correctly recompote
+        // This is dubious as it means that we do not see the alias from an external reference
+        // which has type UniqueRefDenotation instead of SymDenotation. But to correctly recompute
         // the alias we'd need a prefix, which we do not have here. To fix this, we'd have to
         // maintain a prefix in UniqueRefDenotations and JointRefDenotations.
         ref