Depending on the operation, we need to consider gitattributes
in both the work dir and the index. This adds a parameter to
all of the gitattributes related functions that allows user
control of attribute reading behavior (i.e. prefer workdir,
prefer index, only use index).
This fix also covers allowing us to check attributes (and
hence do diff and status) on bare repositories.
This was a somewhat larger change that I hoped because it had
to change the cache key used for gitattributes files.
This also includes droping `git_buf_lasterror` because it makes no sense
in the new system. Note that in most of the places were it has been
dropped, the code needs cleanup. I.e. GIT_ENOMEM is going away, so
instead it should return a generic `-1` and obviously not throw
anything.
The point of having `GIT_ATTR_TRUE` and `GIT_ATTR_FALSE` macros is to be
able to change the way that true and false values are stored inside of
the returned gitattributes value pointer.
However, if these macros are implemented as a simple rename for the
`git_attr__true` pointer, they will always be used with the `==`
operator, and hence we cannot really change the implementation to any
other way that doesn't imply using special pointer values and comparing
them!
We need to do the same thing that core Git does, which is using a
function macro. With `GIT_ATTR_TRUE(attr)`, we can change
internally the way that these values are stored to anything we want.
This commit does that, and rewrites a large chunk of the attributes test
suite to remove duplicated code for expected attributes, and to
properly test the function macro behavior instead of comparing
pointers.
