Subject: Re: [PATCH v2 2/5] reset: introduce --[no-]refresh option to --mixed

From: Victoria Dye <[email-masked]>
Date: Mon, 14 Mar 2022 16:48:54 -0700

Junio C Hamano wrote:
> "Victoria Dye via GitGitGadget" <[email-masked]> writes:
> 
>> From: Victoria Dye <[email-masked]>
>>
>> Add a new --[no-]refresh option that is intended to explicitly determine
>> whether a mixed reset should end in an index refresh.
>>
>> Starting at 9ac8125d1a (reset: don't compute unstaged changes after reset
>> when --quiet, 2018-10-23), using the '--quiet' option results in skipping
>> the call to 'refresh_index(...)' at the end of a mixed reset with the goal
>> of improving performance. However, by coupling behavior that modifies the
>> index with the option that silences logs, there is no way for users to have
>> one without the other (i.e., silenced logs with a refreshed index) without
>> incurring the overhead of a separate call to 'git update-index --refresh'.
>> Furthermore, there is minimal user-facing documentation indicating that
>> --quiet skips the index refresh, potentially leading to unexpected issues
>> executing commands after 'git reset --quiet' that do not themselves refresh
>> the index (e.g., internals of 'git stash', 'git read-tree').
>>
>> To mitigate these issues, '--[no-]refresh' and 'reset.refresh' are
>> introduced to provide a dedicated mechanism for refreshing the index. When
>> either is set, '--quiet' and 'reset.quiet' revert to controlling only
>> whether logs are silenced and do not affect index refresh.
>>
>> Helped-by: Derrick Stolee <[email-masked]>
>> Signed-off-by: Victoria Dye <[email-masked]>
>> ---
>>  Documentation/git-reset.txt |  9 +++++
>>  builtin/reset.c             | 13 ++++++-
>>  t/t7102-reset.sh            | 77 +++++++++++++++++++++++++++++++++----
>>  3 files changed, 91 insertions(+), 8 deletions(-)
> 
> No complaints, but it is somewhat unsatisfying that we need these
> two steps that keep --quiet tied to the decision to or not to
> refresh.  In the longer term, it may be cleaner to completely
> dissociate them, but it probably is not a huge deal.
> 
>> +	/*
>> +	 * If refresh is completely unspecified (either by config or by command
>> +	 * line option), decide based on 'quiet'.
>> +	 */
>> +	if (refresh < 0)
>> +		refresh = !quiet;
> 
> OK.
> 
>> @@ -517,7 +528,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
>>  			if (read_from_tree(&pathspec, &oid, intent_to_add))
>>  				return 1;
>>  			the_index.updated_skipworktree = 1;
>> -			if (!quiet && get_git_work_tree()) {
>> +			if (refresh && get_git_work_tree()) {
>>  				uint64_t t_begin, t_delta_in_ms;
>>  
>>  				t_begin = getnanotime();
> 
> Quite sensible.
> 
>> diff --git a/t/t7102-reset.sh b/t/t7102-reset.sh
>> index d05426062ec..005940778b7 100755
>> --- a/t/t7102-reset.sh
>> +++ b/t/t7102-reset.sh
>> @@ -462,14 +462,77 @@ test_expect_success 'resetting an unmodified path is a no-op' '
>>  	git diff-index --cached --exit-code HEAD
>>  '
>>  
>> +test_index_refreshed () {
>> +
>> +	# To test whether the index is refresh, create a scenario where a
> 
> Doesn't the verb "refresh" refer to the act of making it "fresh"
> (again)?  i.e. update the cached stat info to up-to-date?
> 
> "To test whether the index has been refreshed" or "To test whether
> the cached stat info is up-to-date", perhaps?
> 
>> +	# command will fail if the index is *not* refreshed:
>> +	#   1. update the worktree to match HEAD & remove file2 in the index
> 
> In other words, file2 tentatively becomes untracked.
> 
>> +	#   2. reset --mixed to unstage the change from step 1
> 
> But then, file2 is "added" to the index again, but added from the
> HEAD.  If this did not refresh, then we do not know if the contents
> of the file in the working tree is the same, and "diff-files" may
> say "file2 may be modified".  If "reset" refreshes, this will take
> us back to the same state as "reset --hard HEAD", and "diff-files"
> will not report that "file2" is different.
> 
>> +	#   3. read-tree HEAD~1 (which differs from HEAD in file2)
> 
> With "-m" option, I presume?  Do we want "-u" here, too?
> 
>> +	# If the index is refreshed in step 2, then file2 in the index will be
>> +	# up-to-date with HEAD and read-tree will succeed (thus failing the
>> +	# test). If the index is *not* refreshed, however, the staged deletion
>> +	# of file2 from step 1 will conflict with the changes from the tree read
>> +	# in step 3, resulting in a failure.
> 
> This feels a bit brittle.  The implementation of "read-tree -m" may
> choose to refresh beforehand to avoid such a failure.
> 
> In any case, the name of the helper alone wasn't of any help to
> realize that this is about checking if "reset" refreshes the index
> or not.  Perhaps call it more like
> 
> 	reset_refreshes_index
> 
> or something?
> 
> In any case, instead of the big comment block, comments interspersed
> in the steps may be easier to follow.  
> 
>> +	# Step 0: start with a clean index
>> +	git reset --hard HEAD &&
>> +
>> +	# Step 1
> 	# remove file2 from the index
>> +	git rm --cached file2 &&
>> +
>> +	# Step 2
> 	# resurrect file2 to the index from HEAD; if the cached stat
> 	# info gets refreshed, this brings us back to the state
>         # after Step 0.  If not, "diff-files" would report file2 is
> 	# different.
>> +	git $1 reset $2 --mixed HEAD &&
>> +
>> +	# Step 3
>> +	git read-tree -m HEAD~1
> 
> And use "diff-files file2" here?  Then you do not even have to rely
> on HEAD and HEAD~1 being different at file2.
> 

These are all helpful suggestions, I'll include them in a re-roll
(specifically: rename 'test_index_refreshed' to something mentioning
'reset', move the test comments inline with the steps they execute, and use
'diff-files' rather than 'read-tree'). 

Thanks!