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, 19 insertions, 0 deletions

diff --git a/test/files/neg/t5702-neg-ugly-xbrace.check b/test/files/neg/t5702-neg-ugly-xbrace.check
new file mode 100644
index 0000000000..7d80bbf6be
--- /dev/null
+++ b/test/files/neg/t5702-neg-ugly-xbrace.check
@@ -0,0 +1,19 @@
+t5702-neg-ugly-xbrace.scala:11: error: bad brace or paren after _*
+    val <top>{a, z@_*)</top> = xml
+                     ^
+t5702-neg-ugly-xbrace.scala:12: error: Missing closing brace `}' assumed here
+    println("A for "+ a +", ending with "+ z)
+    ^
+t5702-neg-ugly-xbrace.scala:13: error: in XML literal: in XML content, please use '}}' to express '}'
+  }
+  ^
+t5702-neg-ugly-xbrace.scala:11: error:  I encountered a '}' where I didn't expect one, maybe this tag isn't closed <top>
+    val <top>{a, z@_*)</top> = xml
+         ^
+t5702-neg-ugly-xbrace.scala:14: error: illegal start of simple pattern
+}
+^
+t5702-neg-ugly-xbrace.scala:14: error: '}' expected but eof found.
+}
+ ^
+6 errors found