Support colon in set expressions

[mattigruener]

The names of our sets often contain colons - this should fix parser errors we were seeing. I have also added support for colons to object names.

I guess I have two questions about this:

1. What other special characters do we want to support?
2. How do we want to handle set and object names that contain our set expression operators?

Maybe those two remaining questions boil down to: Do we want object names in gaffer to be more restricted than they currently are? "sphere*&|" is a perfectly valid name at the moment, but it feels like we should only allow [_a-zA-Z0-9][_a-zA-Z0-9:]* maybe? Having a convention like that would make it easier to keep the parser code in sync, I guess...

[johnhaddon]

Thanks Matti,

You might be right that we should be more restrictive in what names we allow to appear in the scene hierarchy, but I think [a-zA-Z0-9:] is probably too restrictive. Minimally we need to bear in mind support for languages other than English, and also what names are allowed in common cache formats and other DCC apps. The core of GafferScene really can support anything because it's just using vector<InternedString>, and treats each path component as just an arbitrary token. The problems really only appear in things like PathMatcher and SetAlgo where we allow paths to be defined as '/' separated strings, and assign special meaning to certain characters. We already support escape characters in StringAlgo::match(), which goes some way to solving the ambiguity ("\*" is a literal '*', not a wildcard for instance), and it could be that using escape characters in SetAlgo and ScenePlug::stringToPath() actually allows us to continue supporting totally general names in the core. It might be nice to keep that generality rather than one day find we've accidentally excluded a particular cache format which is more liberal.

We actually have a Cortex issue open about this already, so I suggest we continue the discussion there. In the meantime I'll merge this...

Cheers...
John