[PATCH] mv: refresh stat info for moved entry

[PATCH] mv: refresh stat info for moved entry

[Victoria Dye via GitGitGadget]

From: Victoria Dye <vdye@github.com>

Add 'refresh_cache_entry()' after moving the index entry in
'rename_index_entry_at()'. Internally, 'git mv' uses
'rename_index_entry_at()' to move the source index entry to the destination,
overwriting the old entry if '-f' is specified. However, it does not refresh
the stat information on destination index entry, making its 'CE_UPTODATE'
flag out-of-date until the index is refreshed (e.g., by 'git status').

Some commands, such as 'git reset', assume the 'CE_UPTODATE' information
they read from the index is accurate, and use that information to determine
whether the operation can be done successfully or not. In order to ensure
the index is correct for commands such as these, explicitly refresh the
destination index entry in 'git mv' before exiting.

Reported-by: Maximilian Reichel <reichemn@icloud.com>
Signed-off-by: Victoria Dye <vdye@github.com>
---
    mv: refresh stat info for moved entry
    
    This patch fixes a bug [1] encountered when executing 'git reset --merge
    HEAD' immediately after 'git mv -f' overwrites an existing index entry.
    Because the 'CE_UPTODATE' flag is not refreshed on the destination entry
    (and therefore incorrectly appeared to not be "up-to-date"), 'git reset
    --merge HEAD' fails when it should otherwise succeed.
    
    To avoid exiting 'git mv' with a stale index that may affect subsequent
    commands, 'rename_index_entry_at()' (used internally by 'git mv') is
    updated to refresh the destination index entry's stat information after
    the move is complete.
    
    [1]
    https://lore.kernel.org/git/84FF8F9A-3A9A-4F2A-8D8E-5D50F2F06203@icloud.com/

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1187%2Fvdye%2Freset%2Fmerge-inconsistency-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1187/vdye/reset/merge-inconsistency-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1187

 read-cache.c  |  1 +
 t/t7001-mv.sh | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/read-cache.c b/read-cache.c
index 1ad56d02e1d..2c5ccc48d6c 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -148,6 +148,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
 	untracked_cache_remove_from_index(istate, old_entry->name);
 	remove_index_entry_at(istate, nr);
 	add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
+	refresh_cache_entry(istate, new_entry, CE_MATCH_REFRESH);
 }
 
 void fill_stat_data(struct stat_data *sd, struct stat *st)
diff --git a/t/t7001-mv.sh b/t/t7001-mv.sh
index 963356ba5f9..ab8607678e7 100755
--- a/t/t7001-mv.sh
+++ b/t/t7001-mv.sh
@@ -4,6 +4,17 @@ test_description='git mv in subdirs'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-diff-data.sh
 
+test_expect_success 'mv -f refreshes updated index entry' '
+	echo test >bar &&
+	git add bar &&
+	git commit -m test &&
+
+	echo foo >foo &&
+	git add foo &&
+	git mv -f foo bar &&
+	git reset --merge HEAD
+'
+
 test_expect_success 'prepare reference tree' '
 	mkdir path0 path1 &&
 	COPYING_test_data >path0/COPYING &&

base-commit: a68dfadae5e95c7f255cf38c9efdcbc2e36d1931
-- 
gitgitgadget

Re: [PATCH] mv: refresh stat info for moved entry

[Derrick Stolee]

On 3/24/2022 9:56 PM, Victoria Dye via GitGitGadget wrote:
> From: Victoria Dye <vdye@github.com>
> 
> Add 'refresh_cache_entry()' after moving the index entry in
> 'rename_index_entry_at()'. Internally, 'git mv' uses
> 'rename_index_entry_at()' to move the source index entry to the destination,
> overwriting the old entry if '-f' is specified. However, it does not refresh
> the stat information on destination index entry, making its 'CE_UPTODATE'
> flag out-of-date until the index is refreshed (e.g., by 'git status').
> 
> Some commands, such as 'git reset', assume the 'CE_UPTODATE' information
> they read from the index is accurate, and use that information to determine
> whether the operation can be done successfully or not. In order to ensure
> the index is correct for commands such as these, explicitly refresh the
> destination index entry in 'git mv' before exiting.

Good find. Thanks for the fix!

> Reported-by: Maximilian Reichel <reichemn@icloud.com>

Thanks for the report, Maximilian!

> @@ -148,6 +148,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
>  	untracked_cache_remove_from_index(istate, old_entry->name);
>  	remove_index_entry_at(istate, nr);
>  	add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
> +	refresh_cache_entry(istate, new_entry, CE_MATCH_REFRESH);

It certainly seems reasonable to add this line. I was unfamiliar
with this method, and it is used only twice: when creating a new
cache entry in make_cache_entry() and in merge-recursive.c's
add_cache_info(). So, it is currently acting in the case of a
newly-inserted cache entry in its existing cases, and here in
'git mv' that's essentially what we are doing (deleting the old
and adding a new would be more appropriate than just moving the
old one).

I took a brief detour thinking about performance, but this is
run only once per command-line argument, so any new overhead
is minimal.
  
> +test_expect_success 'mv -f refreshes updated index entry' '
> +	echo test >bar &&
> +	git add bar &&
> +	git commit -m test &&
> +
> +	echo foo >foo &&
> +	git add foo &&
> +	git mv -f foo bar &&
> +	git reset --merge HEAD

Is there any post-condition on the index that we want to check here?

That is, is there anything that we could notice via 'git status' or
similar that would break before this patch (assuming we put a
test_might_fail in front of the 'git reset --merge HEAD' line)?

Thanks,
-Stolee

Re: [PATCH] mv: refresh stat info for moved entry

[Victoria Dye]

Derrick Stolee wrote:
> On 3/24/2022 9:56 PM, Victoria Dye via GitGitGadget wrote:
>> From: Victoria Dye <vdye@github.com>
>>
>> Add 'refresh_cache_entry()' after moving the index entry in
>> 'rename_index_entry_at()'. Internally, 'git mv' uses
>> 'rename_index_entry_at()' to move the source index entry to the destination,
>> overwriting the old entry if '-f' is specified. However, it does not refresh
>> the stat information on destination index entry, making its 'CE_UPTODATE'
>> flag out-of-date until the index is refreshed (e.g., by 'git status').
>>
>> Some commands, such as 'git reset', assume the 'CE_UPTODATE' information
>> they read from the index is accurate, and use that information to determine
>> whether the operation can be done successfully or not. In order to ensure
>> the index is correct for commands such as these, explicitly refresh the
>> destination index entry in 'git mv' before exiting.
> 
> Good find. Thanks for the fix!
> 
>> Reported-by: Maximilian Reichel <reichemn@icloud.com>
> 
> Thanks for the report, Maximilian!
> 
>> @@ -148,6 +148,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
>>  	untracked_cache_remove_from_index(istate, old_entry->name);
>>  	remove_index_entry_at(istate, nr);
>>  	add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
>> +	refresh_cache_entry(istate, new_entry, CE_MATCH_REFRESH);
> 
> It certainly seems reasonable to add this line. I was unfamiliar
> with this method, and it is used only twice: when creating a new
> cache entry in make_cache_entry() and in merge-recursive.c's
> add_cache_info(). So, it is currently acting in the case of a
> newly-inserted cache entry in its existing cases, and here in
> 'git mv' that's essentially what we are doing (deleting the old
> and adding a new would be more appropriate than just moving the
> old one).
> 
> I took a brief detour thinking about performance, but this is
> run only once per command-line argument, so any new overhead
> is minimal.
>   
>> +test_expect_success 'mv -f refreshes updated index entry' '
>> +	echo test >bar &&
>> +	git add bar &&
>> +	git commit -m test &&
>> +
>> +	echo foo >foo &&
>> +	git add foo &&
>> +	git mv -f foo bar &&
>> +	git reset --merge HEAD
> 
> Is there any post-condition on the index that we want to check here?
> 
> That is, is there anything that we could notice via 'git status' or
> similar that would break before this patch (assuming we put a
> test_might_fail in front of the 'git reset --merge HEAD' line)?
> 

While looking into this, I realized 1) that I wasn't actually refreshing the
cache entry because 'refresh_cache_entry' doesn't work in-place (will fix in
the next version) and 2) the test was only passing because of a race
condition that (as of right now) I can't quite figure out. 

If I add a 'sleep 1' after the 'git add', the test behaves as I expect:
fails when 'mv' doesn't refresh the entry, passes when it does. However,
when the sleep *isn't* there and I'm testing 'git mv' without the refresh,
most of the time the test *doesn't* fail (sometimes it does, but not
reliably). I'm going to try finding the root cause of that before sending
V2, in case I'm missing something else that should be fixed.

But to answer your question, yes - 'git diff-files' will produce an empty
result if the cache is reset properly, and will be non-empty if it is not.
I'll include that in the re-roll as well. 

> Thanks,
> -Stolee

Re: [PATCH] mv: refresh stat info for moved entry

[Junio C Hamano]

"Victoria Dye via GitGitGadget" <gitgitgadget@gmail.com> writes:

> diff --git a/read-cache.c b/read-cache.c
> index 1ad56d02e1d..2c5ccc48d6c 100644
> --- a/read-cache.c
> +++ b/read-cache.c
> @@ -148,6 +148,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
>  	untracked_cache_remove_from_index(istate, old_entry->name);
>  	remove_index_entry_at(istate, nr);
>  	add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
> +	refresh_cache_entry(istate, new_entry, CE_MATCH_REFRESH);
>  }

This is a bit unforunate.

If we are renaming "foo" to "bar", I wonder if we can grab the
cached stat info before calling remove_index_entry_at() for "foo"
and copy it to the new entry we create for "bar".  After all, we
would be making a corresponding change to rename from "foo" to "bar"
at the filesystem level, too, no?

Well, we are already doing that by calling copy_cache_entry().  So
why do we further need to refresh the cache entry in the first
place?  There is something fishy going on, isn't it?

Puzzling...

In any case, refresh_cache_entry() either returns ce or create a
newly allocated entry, so you'd want to first refresh and then the
add the cache entry returned from the function to the index, I
think.

Thanks.

Re: [PATCH] mv: refresh stat info for moved entry

[Victoria Dye]

Junio C Hamano wrote:
> "Victoria Dye via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> diff --git a/read-cache.c b/read-cache.c
>> index 1ad56d02e1d..2c5ccc48d6c 100644
>> --- a/read-cache.c
>> +++ b/read-cache.c
>> @@ -148,6 +148,7 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
>>  	untracked_cache_remove_from_index(istate, old_entry->name);
>>  	remove_index_entry_at(istate, nr);
>>  	add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
>> +	refresh_cache_entry(istate, new_entry, CE_MATCH_REFRESH);
>>  }
> 
> This is a bit unforunate.
> 
> If we are renaming "foo" to "bar", I wonder if we can grab the
> cached stat info before calling remove_index_entry_at() for "foo"
> and copy it to the new entry we create for "bar".  After all, we
> would be making a corresponding change to rename from "foo" to "bar"
> at the filesystem level, too, no?
> 
> Well, we are already doing that by calling copy_cache_entry().  So
> why do we further need to refresh the cache entry in the first
> place?  There is something fishy going on, isn't it?
> 

After some more debugging, I found that the exact trigger for the "not
uptodate" error is a mismatch between the 'ctime' logged in the index entry
and the 'ctime' found on disk. Because we're copying stat information over
directly from the original index entry in 'git mv', the 'ctime' does *not*
reflect the time of file renaming, leading to the error later.

I think this explains all of the behavior we've seen so far:

1. Any index-refreshing operation run after 'git mv' would prevent the 'git
   reset --merge' error, since the ctime would be updated.
2. The error doesn't happen when the file is created within ~1 second of the
   'git mv' (noticed in the test earlier today [1]), since the 'ctime' would
   be seen as "matching" between the index and on-disk.
3. Adding 'refresh_cache_entry()' (and assigning the return value properly,
   unlike in V1 of this patch) avoids the error for the same reason as #1.

So, based on that, I think a "refresh" at the end of
'rename_index_entry_at()' is still needed, but only the stat info needs to
be updated. If that sounds reasonable, I'll send V2 with that change and
update the test to more appropriately test this scenario. 

Thanks!

[1] https://lore.kernel.org/git/d03a34e6-d6a7-6ddb-5784-57078e32ab89@github.com/

> Puzzling...
> 
> In any case, refresh_cache_entry() either returns ce or create a
> newly allocated entry, so you'd want to first refresh and then the
> add the cache entry returned from the function to the index, I
> think.
> 
> Thanks.

[PATCH v2] mv: refresh stat info for moved entry

[Victoria Dye via GitGitGadget]

From: Victoria Dye <vdye@github.com>

Update the stat info of the moved index entry in 'rename_index_entry_at()'
if the entry is up-to-date with the index. Internally, 'git mv' uses
'rename_index_entry_at()' to move the source index entry to the destination.
However, it directly copies the stat info of the original cache entry, which
will not reflect the 'ctime' of the file renaming operation that happened as
part of the move. If a file is otherwise up-to-date with the index, that
difference in 'ctime' will make the entry appear out-of-date until the next
index-refreshing operation (e.g., 'git status').

Some commands, such as 'git reset', use the cached stat information to
determine whether a file is up-to-date; if this information is incorrect,
the command will fail when it should pass. In order to ensure a moved entry
is evaluated as 'up-to-date' when appropriate, refresh the destination index
entry's stat info in 'git mv' if and only if the file is up-to-date.

Note that the test added in 't7001-mv.sh' requires a "sleep 1" to ensure the
'ctime' of the file creation will be definitively older than the 'ctime' of
the renamed file in 'git mv'.

Reported-by: Maximilian Reichel <reichemn@icloud.com>
Signed-off-by: Victoria Dye <vdye@github.com>
---
    mv: refresh stat info for moved entry
    
    This patch fixes a bug [1] encountered when executing 'git reset --merge
    HEAD' immediately after 'git mv'. Because the stat info of the original
    entry is copied to the new one, including all cached stat information,
    the 'ctime' isn't updated corresponding to the rename. If the index
    entry is otherwise up-to-date with the contents on-disk, the incorrect
    'ctime' makes subsequent operations (e.g., 'git reset --merge') identify
    the index entry as out-of-date, failing when they should succeed.
    
    Note, however, that we use 'refresh_cache_entry()' to refresh the stat
    information rather than 'fill_stat_cache_info()' directly because the
    stat information should only be updated if the index entry is up-to-date
    with the file on-disk. If we ignored this distinction, the stat info
    would match the state of unstaged changes on-disk, not the entry in the
    index as it should.
    
    To avoid exiting 'git mv' with a stale index that may affect subsequent
    commands, 'rename_index_entry_at()' (used internally by 'git mv') is
    updated to refresh the destination index entry's stat information after
    the move is complete.
    
    [1]
    https://lore.kernel.org/git/84FF8F9A-3A9A-4F2A-8D8E-5D50F2F06203@icloud.com/
    
    
    Changes since V1
    ================
    
     * Determined the exact cause of the failure (the mismatched 'ctime'),
       as well as the reasoning for why the stat information cannot always
       be updated; revised the implementation accordingly.
     * Fixed usage of 'refresh_cache_entry()'; because it does not update
       cache entries in-place, insert its return value into the index (if
       valid), and discard the no-longer-needed 'new_entry' cache entry.
     * Updated the test for the bug report scenario to wait long enough such
       that the 'ctime' of the 'mv' is distinct from the original file
       creation time.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1187%2Fvdye%2Freset%2Fmerge-inconsistency-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1187/vdye/reset/merge-inconsistency-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/1187

Range-diff vs v1:

 1:  fe9f5f0d8ec ! 1:  bde58070eda mv: refresh stat info for moved entry
     @@ Metadata
       ## Commit message ##
          mv: refresh stat info for moved entry
      
     -    Add 'refresh_cache_entry()' after moving the index entry in
     -    'rename_index_entry_at()'. Internally, 'git mv' uses
     -    'rename_index_entry_at()' to move the source index entry to the destination,
     -    overwriting the old entry if '-f' is specified. However, it does not refresh
     -    the stat information on destination index entry, making its 'CE_UPTODATE'
     -    flag out-of-date until the index is refreshed (e.g., by 'git status').
     +    Update the stat info of the moved index entry in 'rename_index_entry_at()'
     +    if the entry is up-to-date with the index. Internally, 'git mv' uses
     +    'rename_index_entry_at()' to move the source index entry to the destination.
     +    However, it directly copies the stat info of the original cache entry, which
     +    will not reflect the 'ctime' of the file renaming operation that happened as
     +    part of the move. If a file is otherwise up-to-date with the index, that
     +    difference in 'ctime' will make the entry appear out-of-date until the next
     +    index-refreshing operation (e.g., 'git status').
      
     -    Some commands, such as 'git reset', assume the 'CE_UPTODATE' information
     -    they read from the index is accurate, and use that information to determine
     -    whether the operation can be done successfully or not. In order to ensure
     -    the index is correct for commands such as these, explicitly refresh the
     -    destination index entry in 'git mv' before exiting.
     +    Some commands, such as 'git reset', use the cached stat information to
     +    determine whether a file is up-to-date; if this information is incorrect,
     +    the command will fail when it should pass. In order to ensure a moved entry
     +    is evaluated as 'up-to-date' when appropriate, refresh the destination index
     +    entry's stat info in 'git mv' if and only if the file is up-to-date.
     +
     +    Note that the test added in 't7001-mv.sh' requires a "sleep 1" to ensure the
     +    'ctime' of the file creation will be definitively older than the 'ctime' of
     +    the renamed file in 'git mv'.
      
          Reported-by: Maximilian Reichel <reichemn@icloud.com>
          Signed-off-by: Victoria Dye <vdye@github.com>
      
       ## read-cache.c ##
     +@@ read-cache.c: static void replace_index_entry(struct index_state *istate, int nr, struct cache
     + 
     + void rename_index_entry_at(struct index_state *istate, int nr, const char *new_name)
     + {
     +-	struct cache_entry *old_entry = istate->cache[nr], *new_entry;
     ++	struct cache_entry *old_entry = istate->cache[nr], *new_entry, *refreshed;
     + 	int namelen = strlen(new_name);
     + 
     + 	new_entry = make_empty_cache_entry(istate, namelen);
      @@ read-cache.c: void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
     + 	cache_tree_invalidate_path(istate, old_entry->name);
       	untracked_cache_remove_from_index(istate, old_entry->name);
       	remove_index_entry_at(istate, nr);
     - 	add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
     -+	refresh_cache_entry(istate, new_entry, CE_MATCH_REFRESH);
     +-	add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
     ++
     ++	/*
     ++	 * Refresh the new index entry. Using 'refresh_cache_entry' ensures
     ++	 * we only update stat info if the entry is otherwise up-to-date (i.e.,
     ++	 * the contents/mode haven't changed). This ensures that we reflect the
     ++	 * 'ctime' of the rename in the index without (incorrectly) updating
     ++	 * the cached stat info to reflect unstaged changes on disk.
     ++	 */
     ++	refreshed = refresh_cache_entry(istate, new_entry, CE_MATCH_REFRESH);
     ++	if (refreshed && refreshed != new_entry) {
     ++		add_index_entry(istate, refreshed, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
     ++		discard_cache_entry(new_entry);
     ++	} else
     ++		add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
       }
       
       void fill_stat_data(struct stat_data *sd, struct stat *st)
     @@ t/t7001-mv.sh: test_description='git mv in subdirs'
      +
      +	echo foo >foo &&
      +	git add foo &&
     ++
     ++	# Wait one second to ensure ctime of rename will differ from original
     ++	# file creation ctime.
     ++	sleep 1 &&
      +	git mv -f foo bar &&
     -+	git reset --merge HEAD
     ++	git reset --merge HEAD &&
     ++
     ++	# Verify the index has been reset
     ++	git diff-files >out &&
     ++	test_must_be_empty out
      +'
      +
       test_expect_success 'prepare reference tree' '


 read-cache.c  | 17 +++++++++++++++--
 t/t7001-mv.sh | 19 +++++++++++++++++++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/read-cache.c b/read-cache.c
index 3e0e7d41837..4df97e185e9 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -134,7 +134,7 @@ static void replace_index_entry(struct index_state *istate, int nr, struct cache
 
 void rename_index_entry_at(struct index_state *istate, int nr, const char *new_name)
 {
-	struct cache_entry *old_entry = istate->cache[nr], *new_entry;
+	struct cache_entry *old_entry = istate->cache[nr], *new_entry, *refreshed;
 	int namelen = strlen(new_name);
 
 	new_entry = make_empty_cache_entry(istate, namelen);
@@ -147,7 +147,20 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
 	cache_tree_invalidate_path(istate, old_entry->name);
 	untracked_cache_remove_from_index(istate, old_entry->name);
 	remove_index_entry_at(istate, nr);
-	add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
+
+	/*
+	 * Refresh the new index entry. Using 'refresh_cache_entry' ensures
+	 * we only update stat info if the entry is otherwise up-to-date (i.e.,
+	 * the contents/mode haven't changed). This ensures that we reflect the
+	 * 'ctime' of the rename in the index without (incorrectly) updating
+	 * the cached stat info to reflect unstaged changes on disk.
+	 */
+	refreshed = refresh_cache_entry(istate, new_entry, CE_MATCH_REFRESH);
+	if (refreshed && refreshed != new_entry) {
+		add_index_entry(istate, refreshed, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
+		discard_cache_entry(new_entry);
+	} else
+		add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
 }
 
 void fill_stat_data(struct stat_data *sd, struct stat *st)
diff --git a/t/t7001-mv.sh b/t/t7001-mv.sh
index 963356ba5f9..a402908142d 100755
--- a/t/t7001-mv.sh
+++ b/t/t7001-mv.sh
@@ -4,6 +4,25 @@ test_description='git mv in subdirs'
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-diff-data.sh
 
+test_expect_success 'mv -f refreshes updated index entry' '
+	echo test >bar &&
+	git add bar &&
+	git commit -m test &&
+
+	echo foo >foo &&
+	git add foo &&
+
+	# Wait one second to ensure ctime of rename will differ from original
+	# file creation ctime.
+	sleep 1 &&
+	git mv -f foo bar &&
+	git reset --merge HEAD &&
+
+	# Verify the index has been reset
+	git diff-files >out &&
+	test_must_be_empty out
+'
+
 test_expect_success 'prepare reference tree' '
 	mkdir path0 path1 &&
 	COPYING_test_data >path0/COPYING &&

base-commit: abf474a5dd901f28013c52155411a48fd4c09922
-- 
gitgitgadget

Re: [PATCH v2] mv: refresh stat info for moved entry

[Derrick Stolee]

On 3/28/2022 9:07 PM, Victoria Dye via GitGitGadget wrote:
> From: Victoria Dye <vdye@github.com>
> 
> Update the stat info of the moved index entry in 'rename_index_entry_at()'
> if the entry is up-to-date with the index. Internally, 'git mv' uses
> 'rename_index_entry_at()' to move the source index entry to the destination.
> However, it directly copies the stat info of the original cache entry, which
> will not reflect the 'ctime' of the file renaming operation that happened as
> part of the move. If a file is otherwise up-to-date with the index, that
> difference in 'ctime' will make the entry appear out-of-date until the next
> index-refreshing operation (e.g., 'git status').
> 
> Some commands, such as 'git reset', use the cached stat information to
> determine whether a file is up-to-date; if this information is incorrect,
> the command will fail when it should pass. In order to ensure a moved entry
> is evaluated as 'up-to-date' when appropriate, refresh the destination index
> entry's stat info in 'git mv' if and only if the file is up-to-date.
> 
> Note that the test added in 't7001-mv.sh' requires a "sleep 1" to ensure the
> 'ctime' of the file creation will be definitively older than the 'ctime' of
> the renamed file in 'git mv'.

Unfortunate that this is necessary, but it seems to be the only way
to handle this because of the interaction with the system clock and
the filesystem. There are several sleeps like this in
t1701-racy-split-index.sh, for example.

>  void rename_index_entry_at(struct index_state *istate, int nr, const char *new_name)
>  {
> -	struct cache_entry *old_entry = istate->cache[nr], *new_entry;
> +	struct cache_entry *old_entry = istate->cache[nr], *new_entry, *refreshed;
>  	int namelen = strlen(new_name);
>  
>  	new_entry = make_empty_cache_entry(istate, namelen);
> @@ -147,7 +147,20 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
>  	cache_tree_invalidate_path(istate, old_entry->name);
>  	untracked_cache_remove_from_index(istate, old_entry->name);
>  	remove_index_entry_at(istate, nr);
> -	add_index_entry(istate, new_entry, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
> +
> +	/*
> +	 * Refresh the new index entry. Using 'refresh_cache_entry' ensures
> +	 * we only update stat info if the entry is otherwise up-to-date (i.e.,
> +	 * the contents/mode haven't changed). This ensures that we reflect the
> +	 * 'ctime' of the rename in the index without (incorrectly) updating
> +	 * the cached stat info to reflect unstaged changes on disk.
> +	 */
> +	refreshed = refresh_cache_entry(istate, new_entry, CE_MATCH_REFRESH);
> +	if (refreshed && refreshed != new_entry) {
> +		add_index_entry(istate, refreshed, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
> +		discard_cache_entry(new_entry);

I'm glad you're checking that both refreshed is non-NULL and not equal
to new_entry. Both are possible results from refresh_cache_entry().

> +test_expect_success 'mv -f refreshes updated index entry' '
> +	echo test >bar &&
> +	git add bar &&
> +	git commit -m test &&
> +
> +	echo foo >foo &&
> +	git add foo &&
> +
> +	# Wait one second to ensure ctime of rename will differ from original
> +	# file creation ctime.
> +	sleep 1 &&
> +	git mv -f foo bar &&
> +	git reset --merge HEAD &&
> +
> +	# Verify the index has been reset
> +	git diff-files >out &&
> +	test_must_be_empty out
> +'
> +

New test looks good.

Thanks,
-Stolee

Re: [PATCH v2] mv: refresh stat info for moved entry

[Junio C Hamano]

Derrick Stolee <derrickstolee@github.com> writes:

>> Note that the test added in 't7001-mv.sh' requires a "sleep 1" to ensure the
>> 'ctime' of the file creation will be definitively older than the 'ctime' of
>> the renamed file in 'git mv'.
>
> Unfortunate that this is necessary, but it seems to be the only way
> to handle this because of the interaction with the system clock and
> the filesystem. There are several sleeps like this in
> t1701-racy-split-index.sh, for example.

Does "test-tool chmtime" to tweak the filesystem timestamp help?  I
didn't look at the specific step that uses sleep to work around.

>> +
>> +	/*
>> +	 * Refresh the new index entry. Using 'refresh_cache_entry' ensures
>> +	 * we only update stat info if the entry is otherwise up-to-date (i.e.,
>> +	 * the contents/mode haven't changed). This ensures that we reflect the
>> +	 * 'ctime' of the rename in the index without (incorrectly) updating
>> +	 * the cached stat info to reflect unstaged changes on disk.
>> +	 */
>> +	refreshed = refresh_cache_entry(istate, new_entry, CE_MATCH_REFRESH);
>> +	if (refreshed && refreshed != new_entry) {
>> +		add_index_entry(istate, refreshed, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
>> +		discard_cache_entry(new_entry);
>
> I'm glad you're checking that both refreshed is non-NULL and not equal
> to new_entry. Both are possible results from refresh_cache_entry().

;-)

Re: [PATCH v2] mv: refresh stat info for moved entry

[Derrick Stolee]

On 3/29/2022 12:44 PM, Junio C Hamano wrote:
> Derrick Stolee <derrickstolee@github.com> writes:
> 
>>> Note that the test added in 't7001-mv.sh' requires a "sleep 1" to ensure the
>>> 'ctime' of the file creation will be definitively older than the 'ctime' of
>>> the renamed file in 'git mv'.
>>
>> Unfortunate that this is necessary, but it seems to be the only way
>> to handle this because of the interaction with the system clock and
>> the filesystem. There are several sleeps like this in
>> t1701-racy-split-index.sh, for example.
> 
> Does "test-tool chmtime" to tweak the filesystem timestamp help?  I
> didn't look at the specific step that uses sleep to work around.

The issue here is related to ctime, which is not modified by that
helper. It also uses utime() which does not seem to have a way to
modify ctime (which makes sense).

Thanks,
-Stolee

Re: [PATCH v2] mv: refresh stat info for moved entry

[Junio C Hamano]

Derrick Stolee <derrickstolee@github.com> writes:

>> Does "test-tool chmtime" to tweak the filesystem timestamp help?  I
>> didn't look at the specific step that uses sleep to work around.
>
> The issue here is related to ctime, which is not modified by that
> helper. It also uses utime() which does not seem to have a way to
> modify ctime (which makes sense).

Ahh, silly me.  You're right.