Use plain words for duplicate selector

Author: som-snytt

src/compiler/scala/tools/nsc/ast/parser/Parsers.scala

@@ -2825,9 +2825,11 @@ self =>
             if (!h.isMask)
               t.find(_.rename == h.rename).foreach { duplicate =>
                 val msg =
-                  if (h.isRename || duplicate.isRename) s"${h.rename} is an ambiguous name on import"
+                  if (h.isRename || duplicate.isRename)
+                    if (h.name == duplicate.name) s"${h.name} is renamed twice to ${h.rename}"
+                    else s"${h.rename} is an ambiguous name on import"
                   else s"${h.rename} is imported twice"
-                syntaxError(h.renamePos, msg)
+                syntaxError(duplicate.renamePos, msg)
               }
             h :: checkSelectors(t)
           }

test/files/neg/t12813.check

@@ -1,16 +1,16 @@
 t12813.scala:5: error: a is imported twice
 import O.{a, a}   // error
-          ^
-t12813.scala:8: error: b is an ambiguous name on import
+             ^
+t12813.scala:8: error: a is renamed twice to b
 import O.{a => b, a => b}   // error
-               ^
+                       ^
 t12813.scala:10: error: b is an ambiguous name on import
 import O.{a => b, toString => b}    // error
-               ^
+                              ^
 t12813.scala:11: error: toString is an ambiguous name on import
 import O.{a => toString, toString}  // error
-               ^
+                         ^
 t12813.scala:12: error: toString is an ambiguous name on import
 import O.{toString, a => toString}  // error
-          ^
+                         ^
 5 errors

test/files/neg/t12813b.check

@@ -1,18 +1,18 @@
 t12813b.scala:5: error: a is imported twice
 import O.{a, a}   // error
-          ^
-t12813b.scala:8: error: b is an ambiguous name on import
+             ^
+t12813b.scala:8: error: a is renamed twice to b
 import O.{a => b, a => b}   // error
-               ^
+                       ^
 t12813b.scala:10: error: b is an ambiguous name on import
 import O.{a => b, toString => b}    // error
-               ^
+                              ^
 t12813b.scala:11: error: toString is an ambiguous name on import
 import O.{a => toString, toString}  // error
-               ^
+                         ^
 t12813b.scala:12: error: toString is an ambiguous name on import
 import O.{toString, a => toString}  // error
-          ^
+                         ^
 t12813b.scala:14: error: wildcard import must be in last position
 import O.{given, a, _}    // error 3
           ^

test/files/neg/t12813c.check

@@ -1,4 +1,4 @@
-t12813c.scala:6: error: abcdefghij is an ambiguous name on import
+t12813c.scala:6: error: a is renamed twice to abcdefghij
 import O.{a => abcdefghij, a => abcdefghij}
-               ^
+                                ^
 1 error