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, 29 insertions, 0 deletions

diff --git a/test/files/neg/t5702-neg-bad-and-wild.scala b/test/files/neg/t5702-neg-bad-and-wild.scala
new file mode 100644
index 0000000000..3833a002b1
--- /dev/null
+++ b/test/files/neg/t5702-neg-bad-and-wild.scala
@@ -0,0 +1,29 @@
+
+object Test {
+  case class K(i: Int)
+
+  def main(args: Array[String]) {
+    val k = new K(9)
+    val is = List(1,2,3)
+
+    is match {
+      case List(1, _*,) => // bad use of _* (a sequence pattern must be the last pattern)
+                           // illegal start of simple pattern
+      case List(1, _*3,) => // illegal start of simple pattern
+      //case List(1, _*3:) =>  // poor recovery by parens
+      case List(1, x*) => // use _* to match a sequence
+      case List(x*, 1) => // trailing * is not a valid pattern
+      case (1, x*) => // trailing * is not a valid pattern
+      case (1, x@_*) => // bad use of _* (sequence pattern not allowed)
+    }
+
+// good syntax, bad semantics, detected by typer
+//gowild.scala:14: error: star patterns must correspond with varargs parameters
+    val K(is @ _*) = k
+    val K(ns @ _*, x) = k // bad use of _* (a sequence pattern must be the last pattern)
+    val (b, _ * ) = Pair(5,6) // bad use of _* (sequence pattern not allowed)
+// no longer complains
+//bad-and-wild.scala:15: error: ')' expected but '}' found.
+  }
+}
+