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

> 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 difference in 'ctime' will make the entry appear out-of-date until the next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'.

>  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);

> +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
> +'
> +