SI-5702 Pattern parser halts on star

In patterns, the parser halts when it sees stars.
This means it does not handle infix notation for a case class
named "*".  This patch uses lookahead to decide whether to parse
'_' '*' as a sequence pattern or as the start of infix.
(For both normal and error cases, the tokens are always consumed
immediately.) Error messages are improved for _* (as a help to learners)
and slightly improved recovery helps the parse continue.
The entry point for XML patterns is now distinct; otherwise,
the change is local to pattern3-simplepattern; the entry point
for simplepattern() is unchanged because it is commented
"hook for IDE."

1 files changed, 5 insertions, 19 deletions

diff --git a/test/files/neg/t1878.check b/test/files/neg/t1878.check
index b47367e12c..ac2071c3d8 100644
--- a/test/files/neg/t1878.check
+++ b/test/files/neg/t1878.check
@@ -1,21 +1,7 @@
-t1878.scala:3: error: _* may only come last
+t1878.scala:3: error: bad use of _* (a sequence pattern must be the last pattern)
   val err1 = "" match { case Seq(f @ _*, ',') => f }
-                                 ^
-t1878.scala:3: error: scrutinee is incompatible with pattern type;
- found   : Seq[A]
- required: String
-  val err1 = "" match { case Seq(f @ _*, ',') => f }
-                                ^
-t1878.scala:3: error: not found: value f
-  val err1 = "" match { case Seq(f @ _*, ',') => f }
-                                                 ^
-t1878.scala:3: error: value _2 is not a member of object Seq
-  val err1 = "" match { case Seq(f @ _*, ',') => f }
-             ^
-t1878.scala:9: error: _* may only come last
+                                       ^
+t1878.scala:9: error: bad use of _* (a sequence pattern must be the last pattern)
   val List(List(_*, arg2), _) = List(List(1,2,3), List(4,5,6))
-                 ^
-t1878.scala:13: error: _* may only come last
-    case <p> { _* } </p> =>
-                ^
-6 errors found
+                  ^
+two errors found