ENH: Extend the regex for rank/alpha pattern (#2419)
Supersedes #2382
Right now, the regex used to match the keys passed for rank_pattern and
alpha_pattern requires that either:
1. The module name is identical to the key
2. The module name having a prefix and then ending on the key
This is restrictive, since it doesn't allow to disambiguate between all
cases. E.g. if we have a model with these attributes:
- model.foo
- model.bar.foo
We cannot currently target just model.foo. (We can already target only
model.bar.foo by passing "bar.foo" as a key to the rank_pattern /
alpha_pattern dict).
This PR makes it possible to pass "^foo" as a key. This way,
model.bar.foo is not targeted, as the key does not start with "foo".
As a general rule for users, if they intend to have a full match, they
should pass the full name of the module preceded by a ^. This is the
least ambigious way.
When running the test case with the old code, all the test cases with ^
will fail, which is fine, since ^ was not working anyway. At the same
time, all test cases not using ^ pass, which means they are backwards
compatible.
