SI-7074 Fix xml attribute sorting

Sorting the attributes of an xml element could drop some of the
attributes. It was caused by the incorrect use of MetaData#copy() to
concatenate "smaller" with the rest of the attributes. The
MetaData#copy() method is similar to the following hypothetical method
on a List:

def copy(other: List): List = head :: other

The fix prepends all elements of "smaller" to the rest of the attributes
in the proper order.

Author: khernyo

src/library/scala/xml/Utility.scala

@@ -64,7 +64,7 @@ object Utility extends AnyRef with parsing.TokenTests {
     val key = md.key
     val smaller = sort(md.filter { m => m.key < key })
     val greater = sort(md.filter { m => m.key > key })
-    smaller.copy(md.copy ( greater ))
+    smaller.foldRight (md copy greater) ((x, xs) => x copy xs)
   }
 
   /** Return the node with its attribute list sorted alphabetically

test/files/run/t7074.check

@@ -0,0 +1,9 @@
+<a/>
+<a b="2" c="3" d="1"/>
+<a b="2" c="4" d="1" e="3" f="5"/>
+<a b="5" c="4" d="3" e="2" f="1"/>
+<a b="1" c="2" d="3" e="4" f="5"/>
+<a a:b="2" a:c="3" a:d="1"/>
+<a a:b="2" a:c="4" a:d="1" a:e="3" a:f="5"/>
+<a a:b="5" a:c="4" a:d="3" a:e="2" a:f="1"/>
+<a a:b="1" a:c="2" a:d="3" a:e="4" a:f="5"/>

test/files/run/t7074.scala

@@ -0,0 +1,15 @@
+import scala.xml.Utility.sort
+
+object Test extends App {
+  println(sort(<a/>))
+  println(sort(<a d="1" b="2" c="3"/>))
+  println(sort(<a d="1" b="2" e="3" c="4" f="5"/>))
+  println(sort(<a f="1" e="2" d="3" c="4" b="5"/>))
+  println(sort(<a b="1" c="2" d="3" e="4" f="5"/>))
+
+  println(sort(<a a:d="1" a:b="2" a:c="3"/>))
+  println(sort(<a a:d="1" a:b="2" a:e="3" a:c="4" a:f="5"/>))
+  println(sort(<a a:f="1" a:e="2" a:d="3" a:c="4" a:b="5"/>))
+  println(sort(<a a:b="1" a:c="2" a:d="3" a:e="4" a:f="5"/>))
+}
+