Hi Elijah,
On Fri, 11 Oct 2019, Elijah Newren via GitGitGadget wrote:
> From: Elijah Newren <newren@xxxxxxxxx>
>
> Dscho noted a few things making this function hard to follow.
> Restructure it a bit and add comments to make it easier to follow. The
> restructurings include:
>
> * There was a special case if-check at the end of the function
> checking whether someone just renamed a file within its original
> directory, meaning that there could be no directory rename involved.
> That check was slightly convoluted; it could be done in a more
> straightforward fashion earlier in the function, and can be done
> more cheaply too (no call to strncmp).
>
> * The conditions for advancing end_of_old and end_of_new before
> calling strchr were both confusing and unnecessary. If either
> points at a '/', then they need to be advanced in order to find the
> next '/'. If either doesn't point at a '/', then advancing them one
> char before calling strchr() doesn't hurt. So, just rip out the
> if conditions and advance both before calling strchr().
>
> Signed-off-by: Elijah Newren <newren@xxxxxxxxx>
This commit message, as well as the patch, make a lot of sense to me.
Thank you for doing this!
Ciao,
Dscho
> ---
> merge-recursive.c | 60 ++++++++++++++++++++++++++++-------------------
> 1 file changed, 36 insertions(+), 24 deletions(-)
>
> diff --git a/merge-recursive.c b/merge-recursive.c
> index 22a12cfeba..f80e48f623 100644
> --- a/merge-recursive.c
> +++ b/merge-recursive.c
> @@ -1943,8 +1943,8 @@ static void get_renamed_dir_portion(const char *old_path, const char *new_path,
> char **old_dir, char **new_dir)
> {
> char *end_of_old, *end_of_new;
> - int old_len, new_len;
>
> + /* Default return values: NULL, meaning no rename */
> *old_dir = NULL;
> *new_dir = NULL;
>
> @@ -1955,43 +1955,55 @@ static void get_renamed_dir_portion(const char *old_path, const char *new_path,
> * "a/b/c/d" was renamed to "a/b/some/thing/else"
> * so, for this example, this function returns "a/b/c/d" in
> * *old_dir and "a/b/some/thing/else" in *new_dir.
> - *
> - * Also, if the basename of the file changed, we don't care. We
> - * want to know which portion of the directory, if any, changed.
> + */
> +
> + /*
> + * If the basename of the file changed, we don't care. We want
> + * to know which portion of the directory, if any, changed.
> */
> end_of_old = strrchr(old_path, '/');
> end_of_new = strrchr(new_path, '/');
> -
> if (end_of_old == NULL || end_of_new == NULL)
> - return;
> + return; /* We haven't modified *old_dir or *new_dir yet. */
> +
> + /* Find the first non-matching character traversing backwards */
> while (*--end_of_new == *--end_of_old &&
> end_of_old != old_path &&
> end_of_new != new_path)
> ; /* Do nothing; all in the while loop */
> +
> /*
> - * We've found the first non-matching character in the directory
> - * paths. That means the current directory we were comparing
> - * represents the rename. Move end_of_old and end_of_new back
> - * to the full directory name.
> + * If both got back to the beginning of their strings, then the
> + * directory didn't change at all, only the basename did.
> */
> - if (*end_of_old == '/')
> - end_of_old++;
> - if (*end_of_old != '/')
> - end_of_new++;
> - end_of_old = strchr(end_of_old, '/');
> - end_of_new = strchr(end_of_new, '/');
> + if (end_of_old == old_path && end_of_new == new_path &&
> + *end_of_old == *end_of_new)
> + return; /* We haven't modified *old_dir or *new_dir yet. */
>
> /*
> - * It may have been the case that old_path and new_path were the same
> - * directory all along. Don't claim a rename if they're the same.
> + * We've found the first non-matching character in the directory
> + * paths. That means the current characters we were looking at
> + * were part of the first non-matching subdir name going back from
> + * the end of the strings. Get the whole name by advancing both
> + * end_of_old and end_of_new to the NEXT '/' character. That will
> + * represent the entire directory rename.
> + *
> + * The reason for the increment is cases like
> + * a/b/star/foo/whatever.c -> a/b/tar/foo/random.c
> + * After dropping the basename and going back to the first
> + * non-matching character, we're now comparing:
> + * a/b/s and a/b/
> + * and we want to be comparing:
> + * a/b/star/ and a/b/tar/
> + * but without the pre-increment, the one on the right would stay
> + * a/b/.
> */
> - old_len = end_of_old - old_path;
> - new_len = end_of_new - new_path;
> + end_of_old = strchr(++end_of_old, '/');
> + end_of_new = strchr(++end_of_new, '/');
>
> - if (old_len != new_len || strncmp(old_path, new_path, old_len)) {
> - *old_dir = xstrndup(old_path, old_len);
> - *new_dir = xstrndup(new_path, new_len);
> - }
> + /* Copy the old and new directories into *old_dir and *new_dir. */
> + *old_dir = xstrndup(old_path, end_of_old - old_path);
> + *new_dir = xstrndup(new_path, end_of_new - new_path);
> }
>
> static void remove_hashmap_entries(struct hashmap *dir_renames,
> --
> gitgitgadget
>
>
