Test that entries are only smudged when we write the index: the
entry smudging is to prevent us from updating an index in a way
that it would be impossible to tell that an item was racy.
Consider when we load an index: any entries that have the same
(or newer) timestamp than the index itself are considered racy,
and are subject to further scrutiny.
If we *save* that index with the same entries that we loaded,
then the index would now have a newer timestamp than the entries,
and they would no longer be given that additional scrutiny, failing
our racy detection! So test that we smudge those entries only on
writing the new index, but that we can detect them (in diff) without
having to write.
When there's no matching index entry (for whatever reason), don't
try to dereference the null return value to get at the id.
Otherwise when we break something in the index API, the checkout
test crashes for confusing reasons and causes us to step through
it in a debugger thinking that we had broken much more than we
actually did.
Keep track of entries that we believe are up-to-date, because we
added the index entries since the index was loaded. This prevents
us from unnecessarily examining files that we wrote during the
cleanup of racy entries (when we smudge racily clean files that have
a timestamp newer than or equal to the index's timestamp when we
read it). Without keeping track of this, we would examine every
file that we just checked out for raciness, since all their timestamps
would be newer than the index's timestamp.
When we insert a conflict in a case-insensitive index, accept the
new entry's path as the correct case instead of leaving the path we
already had.
This puts `git_index_conflict_add()` on the same level as
`git_index_add()` in this respect.
Reload the HEAD and index data for a submodule after reading the
configuration. The configuration may specify a `path`, so we must
update HEAD and index data with that path in mind.
When creating a filebuf, detect a directory that exists in our
target file location. This prevents a failure later, when we try
to move the lock file to the destination.
Test that on platforms without `core.symlinks`, we preserve symlinks
in `git_index_add_bypath`. (Users should correct the actual index
entry's mode to change a link to a regular file.)
On platforms that lack `core.symlinks`, we should not go looking for
symbolic links and `p_readlink` their target. Instead, we should
examine the file's contents.
When `core.symlinks = false`, we write the symlinks content (target)
to a regular file. We should ensure that when we later see that
regular file, we treat it specially - and that changing that regular
file would actually change the symlink target. (For compatibility
with Git for Windows).
This reduces the chances of a crash in the thread tests. This shouldn't
affect general usage too much, since the main usage of these functions
are to read into an empty buffer.
Instead of relying on the size and timestamp, which can hide changes
performed in the same second, hash the file content's when we care about
detecting changes.
We currently use the timestamp in order to decide whether a config file
has changed since we last read it.
This scheme falls down if the file is written twice within the same
second, as we fail to detect the file change after the first read in
that second.
