Avoid recomputations of qualifiers of dynamic selects and calls

Author: odersky

compiler/src/dotty/tools/dotc/typer/Inferencing.scala

@@ -38,6 +38,9 @@ object Inferencing {
     result
   }
 
+  /** Try to fully define `tp`. Return whether constraint has changed.
+   *  Any changed constraint is kept.
+   */
   def canDefineFurther(tp: Type)(using Context): Boolean =
     val prevConstraint = ctx.typerState.constraint
     isFullyDefined(tp, force = ForceDegree.all)

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -570,10 +570,11 @@ class Typer extends Namer
       else if qual.tpe.derivesFrom(defn.DynamicClass)
         && selName.isTermName && !isDynamicExpansion(tree)
       then
+        val tree2 = cpy.Select(tree0)(untpd.TypedSplice(qual), selName)
         if pt.isInstanceOf[FunOrPolyProto] || pt == AssignProto then
-          assignType(tree, TryDynamicCallType)
+          assignType(tree2, TryDynamicCallType)
         else
-          typedDynamicSelect(tree0, Nil, pt)
+          typedDynamicSelect(tree2, Nil, pt)
       else
         assignType(tree,
           rawType match