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, 14 insertions, 0 deletions

diff --git a/test/files/neg/t5702-neg-ugly-xbrace.scala b/test/files/neg/t5702-neg-ugly-xbrace.scala
new file mode 100644
index 0000000000..0ff7bfa09d
--- /dev/null
+++ b/test/files/neg/t5702-neg-ugly-xbrace.scala
@@ -0,0 +1,14 @@
+
+object Test {
+  def main(args: Array[String]) {
+
+    val xml = <top><a>apple</a><b>boy</b><c>child</c></top>
+    // This is the more likely typo, and the uglier parse.
+    // We could turn it into a } if } does not follow (to
+    // avoid handing }} back to xml) but that is quite ad hoc.
+    // Assuming } for ) after _* would not be not outlandish.
+    // bad brace or paren after _*
+    val <top>{a, z@_*)</top> = xml
+    println("A for "+ a +", ending with "+ z)
+  }
+}