Make type parameter reordering generally available.

Author: odersky

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

@@ -1490,6 +1490,23 @@ object SymDenotations {
       if (myMemberCache != null) myMemberCache invalidate sym.name
     }
 
+    /** Make sure the type parameters of this class are `tparams`, reorder definitions
+     *  in scope if necessary.
+     *  @pre  All type parameters in `tparams` are entered in class scope `info.decls`.
+     */
+    def updateTypeParams(tparams: List[Symbol])(implicit ctx: Context): Unit =
+      if (!typeParams.corresponds(tparams)(_.name == _.name)) {
+        val decls = info.decls
+        val decls1 = newScope
+        for (tparam <- tparams) decls1.enter(decls.lookup(tparam.name))
+        for (sym <- decls) if (!typeParams.contains(sym)) decls1.enter(sym)
+        val ci = classInfo
+        // dotty deviation; overloading resolution on next line fails if prefix `ci` is not a value.
+        // See test pending/pos/overloaddefault.scala
+        info = ci.derivedClassInfo(decls = decls1)
+        myTypeParams = null
+      }
+
     /** All members of this class that have the given name.
      *  The elements of the returned pre-denotation all
      *  have existing symbols.

src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -130,18 +130,10 @@ object Scala2Unpickler {
     } else {
       registerCompanionPair(scalacCompanion, denot.classSymbol)
     }
-    val declsTypeParams = denot.typeParams
-    val declsInRightOrder =
-      if (declsTypeParams.corresponds(tparams)(_.name == _.name)) decls
-      else { // create new scope with type parameters in right order
-        val decls1 = newScope
-        for (tparam <- tparams) decls1.enter(decls.lookup(tparam.name))
-        for (sym <- decls) if (!declsTypeParams.contains(sym)) decls1.enter(sym)
-        decls1
-      }
 
-    denot.info = ClassInfo( // final info
-      denot.owner.thisType, denot.classSymbol, parentRefs, declsInRightOrder, ost)
+    denot.info = ClassInfo( // final info, except possibly for typeparams ordering
+      denot.owner.thisType, denot.classSymbol, parentRefs, decls, ost)
+    denot.updateTypeParams(tparams)
   }
 }