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merge-recursive: clean up get_renamed_dir_portion()

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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@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Elijah Newren 2019-10-22 21:22:49 +00:00 committed by Junio C Hamano
parent 08da6496b6
commit d3eebaad5e
1 changed files with 38 additions and 26 deletions
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64
merge-recursive.c
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@ -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 */
/*
* 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 == old_path && end_of_new == new_path &&
*end_of_old == *end_of_new)
return; /* We haven't modified *old_dir or *new_dir yet. */
/*
* 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.
* 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/.
*/
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, '/');
end_of_old = strchr(++end_of_old, '/');
end_of_new = strchr(++end_of_new, '/');
/*
* 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.
*/
old_len = end_of_old - old_path;
new_len = end_of_new - new_path;
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,