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From: "Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com>
To: git@vger.kernel.org
Cc: Johannes Schindelin Johannes.Schindelin@gmx.de,
	Junio C Hamano <gitster@pobox.com>,
	Elijah Newren <newren@gmail.com>
Subject: [PATCH v2 1/3] merge-recursive: clean up get_renamed_dir_portion()
Date: Tue, 22 Oct 2019 21:22:49 +0000	[thread overview]
Message-ID: <8ae78679c9066a206610465e1da91a5f575fced2.1571779371.git.gitgitgadget@gmail.com> (raw)
In-Reply-To: <pull.390.v2.git.1571779371.gitgitgadget@gmail.com>

From: Elijah Newren <newren@gmail.com>

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>
---
 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


  reply	other threads:[~2019-10-22 21:22 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-11 20:42 [PATCH 0/2] Dir rename fixes Elijah Newren via GitGitGadget
2019-10-11 20:42 ` [PATCH 1/2] merge-recursive: clean up get_renamed_dir_portion() Elijah Newren via GitGitGadget
2019-10-12 19:47   ` Johannes Schindelin
2019-10-11 20:42 ` [PATCH 2/2] merge-recursive: fix merging a subdirectory into the root directory Elijah Newren via GitGitGadget
2019-10-12 20:37   ` Johannes Schindelin
2019-10-13  0:40     ` Elijah Newren
2019-10-14 10:41       ` Johannes Schindelin
2019-10-22 19:15         ` Elijah Newren
2019-10-24 22:22           ` Johannes Schindelin
2019-10-25  0:12             ` Elijah Newren
2019-10-25 13:30               ` Johannes Schindelin
2019-10-29  1:20                 ` Junio C Hamano
2019-10-30  7:01                   ` Elijah Newren
2019-10-30 22:16                     ` Johannes Schindelin
2019-10-30 22:31                       ` Elijah Newren
2019-10-31  8:28                         ` Johannes Schindelin
2019-10-12 18:41 ` [PATCH 0/2] Dir rename fixes Johannes Schindelin
2019-10-22 21:22 ` [PATCH v2 0/3] " Elijah Newren via GitGitGadget
2019-10-22 21:22   ` Elijah Newren via GitGitGadget [this message]
2019-10-22 21:22   ` [PATCH v2 2/3] merge-recursive: fix merging a subdirectory into the root directory Elijah Newren via GitGitGadget
2019-10-22 21:22   ` [PATCH v2 3/3] t604[236]: do not run setup in separate tests Elijah Newren via GitGitGadget

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