Conversion between Targets and their BUILD aliases.

[gmalmquist]

There should be an easy way to do both:

1. Given a Target type, lookup what BUILD aliases map to it.
2. Given a BUILD file alias, lookup what Target type it corresponds to.

The motivation for this is allowing users to specify the names of BUILD file aliases (such as java_library) as options, which can be read and understood properly by tasks, subsystems, et cetera, rather than having to use internal names like JavaLibrary.

[jsirois]

To be clear - the listed motivating case (an instance of 2. above) already is used / supported like so: https://github.com/pantsbuild/pants/blob/master/src/python/pants/backend/core/tasks/filter.py#L80-L84

[gmalmquist]

Can that be done without a context, as in a subsystem or in a Target etc?

[jsirois]

Nope - so that's a key requirement here then. The given-a-Target-instance case is straightforward for #1. The #2 case without a Context is more interesting, especially if implemented w/o a static global - which would be nice but also push/pull vs the goal here.

[jsirois]

I'll take #1 which is the only case I can currently find need for in the codebase.

[jsirois]

OK - the solution for 1 above is in master @ ad9f848

Do you have a concrete use case for 2 above @gmalmquist? If not I'll close this.

[jsirois]

I'll assign this to you @gmalmquist to close or else keep open / refine for the remaining criteria.

[stuhood]

(2) is possible via self.context.build_file_parser.registered_aliases(), although it is a bit awkward.