revset: check invalid function syntax "func-name"() explicitly
Before the error was caught at func() as an unknown identifier, and the
optimizer failed to detect the syntax error. This patch introduces getsymbol()
helper to ensure that a string is not allowed as a function name.
$ hg init
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls
a
unknown