While we do have a test which checks whether a written index of version
4 has the correct version set, we do not check whether this actually
enables path compression for index entries. This commit adds a new test
by adding a number of index entries with equal path prefixes to the
index and subsequently flushing that to disk. With suffix compression
enabled by index version 4, only the last few bytes of these paths will
actually have to be written to the index, saving a lot of disk space.
For the test, differences are about an order of magnitude, allowing us
to easily verify without taking a deeper look at actual on-disk
contents.
While we have a simple test to determine whether we can write an index
of version 4, we never verified that we are able to read this kind of
index (and in fact, we were not able to do so). Add a new repository
which has an index of version 4. This repository is then read from a new
test.
The init and cleanup functions for test suites are usually prepended to
our actual tests. The index::version test suite does not adhere to this
stile. Fix this.
Support reading and writing index v4. Index v4 uses a very simple
compression scheme for pathnames, but is otherwise similar to index v3.
Signed-off-by: David Turner <dturner@twitter.com>
