On 23/12/2021 00:52, Junio C Hamano wrote:
Ah, there are cases where we do clear active_cache_changed when we
notice that an operation detected an error, to avoid spreading the
breakage by writing the index file out, and I think that is the
right thing to do. Which means that the above patch is not quite
right. Perhaps taking all of the above together, something like
this?
*o->has_errors |= refresh_cache(o->flags | flag);
if (*o->has_errors)
active_cache_changed = 0;
else if (has_racy_timestamps(&the_index))
/*
* Even if nothing else has changed, updating the file
* increases the chance that racy timestamps become
* non-racy, helping future run-time performance.
*/
active_cache_changed |= SOMETHING_CHANGED;
I think it's safe to write the index even if refresh_cache() reports an
"error" and we should actually do that:
The underlying refresh_index() will report an "error" only for "file:
needs merge" and "file: needs update". In both cases, the corresponding
entries will not have been updated. Every entry which has been updated
is good on its own and writing these updates makes the index a little
bit better. Subsequent calls to refresh_index() won't have to do the
same work again (like invoking the quite expensive LFS filter).
This is also how cmd_status() currently works: it does not pay attention
to the return value of refresh_index() and will always write the index
if racy timestamps are encountered.
Overall, the "error" handling in update-index.c might not always do what
one expects. Let's consider your suggested fix. When invoking:
update-index --refresh
this won't fix racy timestamps, however:
update-index --refresh --add untracked
will do. I think this is caused by active_cache_changed being used in
two different ways: to indicate that the cache should be written and to
indicate that it must not be written. It might be a good idea to take
the latter "block index write" to a separate static variable in
update-index.c.
Candidate usages of this new "block index write" variable will be in the
existing callbacks: errors detected in unresolve_callback() should
probably continue to block an index write, to ensure that either all or
none of the specified files will be unresolved. For the
reupdate_callback(), the underlying do_reupdate() seems to return 0
always, so there is dead code in the callback (or am I completely
blind?). To stay on the safe side, we may still continue to block an
index write here. The refresh_callback() will never block an index write.
Does it make sense to clarify error handling in some preceding commit
and only then address the razy timestamps? It will probably make this
second commit clearer.
+}
+
+update_assert_changed() {
+ local ts1=$(test-tool chmtime --get .git/index) &&
+ test_might_fail git update-index $1 &&
+ local ts2=$(test-tool chmtime --get .git/index) &&
+ [ $ts1 -ne $ts2 ]
+}
+
+test_expect_success 'setup' '
+ touch .git/fs-tstamp &&
Not that it is wrong, but do we need to create such a throw-away
file inside the .git directory?
We actually only need a timestamp for which we know that it is before
the timestamp the next file system operation would create. I agree that
it should be easy to rewrite that using "test-tool chmtime". This should
also simplify reset_mtime().
Regarding all other comments, thanks, I'll address them as suggested for
the next patch. And sorry for not checking CodingGuidelines before (I
had completely missed this document).
-Marc
