Move NamedArg puity check

Author: nicolasstucki

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

@@ -370,6 +370,8 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
       exprPurity(expr)
     case Block(stats, expr) =>
       minOf(exprPurity(expr), stats.map(statPurity))
+    case NamedArg(_, expr) =>
+      exprPurity(expr)
     case _ =>
       Impure
   }

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

@@ -617,19 +617,17 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
             typedArgs = liftArgs(argDefBuf, methType, typedArgs)
 
             // Lifted arguments ordered based on the original order of typedArgBuf and
-            // with all non explicit default parameters at the end in declaration order.
+            // with all non-explicit default parameters at the end in declaration order.
             val orderedArgDefs = {
               // List of original arguments that are lifted by liftArgs
-              val impureArgs = typedArgBuf.filterNot {
-                case NamedArg(_, arg) => isPureExpr(arg)
-                case arg => isPureExpr(arg)
-              }
+              val impureArgs = typedArgBuf.filterNot(isPureExpr)
+              // Assuming stable sorting all non-explicit default parameters will remain in the end with the same order
               val defaultParamIndex = args.size
               // Mapping of index of each `liftable` into original args ordering
               val indices = impureArgs.map { arg =>
                 val idx = args.indexOf(arg)
-                if (idx >= 0) idx // original index skipping pure agruments
-                else defaultParamIndex // assuming stable sorting all will remain in the end with the same order
+                if (idx >= 0) idx // original index skipping pure arguments
+                else defaultParamIndex
               }
               scala.util.Sorting.stableSort[(Tree, Int), Int](argDefBuf zip indices, x => x._2).map(_._1)
             }