Simplify TreeTypeMap further

Author: odersky

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

@@ -178,25 +178,25 @@ class TreeTypeMap(
    *  and return a treemap that contains the substitution
    *  between original and mapped symbols.
    */
-  def withMappedSyms(syms: List[Symbol], mapAlways: Boolean = false): TreeTypeMap =
-    withMappedSyms(syms, mapSymbols(syms, this, mapAlways))
+  def withMappedSyms(syms: List[Symbol]): TreeTypeMap =
+    withMappedSyms(syms, mapSymbols(syms, this))
 
   /** The tree map with the substitution between originals `syms`
    *  and mapped symbols `mapped`. Also goes into mapped classes
    *  and substitutes their declarations.
    */
   def withMappedSyms(syms: List[Symbol], mapped: List[Symbol]): TreeTypeMap =
-    val symsChanged = syms ne mapped
-    val substMap = withSubstitution(syms, mapped)
-    lazy val origCls = mapped.zip(syms).filter(_._1.isClass).toMap
-    mapped.filter(_.isClass).foldLeft(substMap) { (tmap, cls) =>
-      val origDcls = cls.info.decls.toList.filterNot(_.is(TypeParam))
-      val mappedDcls = mapSymbols(origDcls, tmap)
-      val tmap1 = tmap.withMappedSyms(
-        origCls(cls).typeParams ::: origDcls,
-        cls.typeParams ::: mappedDcls)
-      if symsChanged then
+    if syms eq mapped then this
+    else
+      val substMap = withSubstitution(syms, mapped)
+      lazy val origCls = mapped.zip(syms).filter(_._1.isClass).toMap
+      mapped.filter(_.isClass).foldLeft(substMap) { (tmap, cls) =>
+        val origDcls = cls.info.decls.toList.filterNot(_.is(TypeParam))
+        val mappedDcls = mapSymbols(origDcls, tmap, mapAlways = true)
+        val tmap1 = tmap.withMappedSyms(
+          origCls(cls).typeParams ::: origDcls,
+          cls.typeParams ::: mappedDcls)
         origDcls.lazyZip(mappedDcls).foreach(cls.asClass.replace)
-      tmap1
-    }
+        tmap1
+      }
 }