[PATCH] diff: document what --name-only shows

From: Junio C Hamano <gitster@pobox.com>
Date: May 17, 2024, 17:14 UTC
Message-ID: <xmqqeda0jr7d.fsf@gitster.g>

The "--name-only" option is about showing the name of each file in the post-image tree that got changed and nothing else (like "was it created?"). Unlike the "--name-status" option that tells how the change happened (e.g., renamed with similarity), it does not give anything else, like the name of the corresponding file in the old tree.

For example, if you start from a clean checkout that has a file whose name is COPYING, here is what you would see:

    $ git mv COPYING RENAMING
    $ git diff -M --name-only HEAD
    RENAMING
    $ git diff -M --name-status HEAD
    R100	COPYING	RENAMING

Lack of the description of this fact has confused readers in the past. Even back when dda2d79a ([PATCH] Clean up diff option descriptions., 2005-07-13) documented "--name-only", "git diff" already supported the renames, so in a sense, from day one, this should have been documented more clearly but it wasn't.

Belatedly clarify it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * In the "how about this" patch, I incorrectly said "before tree",
   in an failed attempt to use fewer jargon, but it was misguided.
   The names are taken from the post-image (i.e. "after") tree, and
   we already use post-image in the same document.

   Also this version uses a bit of grammar trick to rephrase so that
   it is clear that we are talking about a single changed file
   having up to two names by mentioning "each changed file".  That
   way, the phrasing strongly hints that "--name-only" shows only
   the name in the post-image tree while "--name-status" may show
   both names.

 Documentation/diff-options.txt | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 7d73e976d9..0c456dfd0c 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -318,12 +318,13 @@ explained for the configuration variable `core.quotePath` (see
 linkgit:git-config[1]).
 
 --name-only::
-	Show only names of changed files. The file names are often encoded in UTF-8.
+	Show only the name of each changed file in the post-image tree.
+	The file names are often encoded in UTF-8.
 	For more information see the discussion about encoding in the linkgit:git-log[1]
 	manual page.
 
 --name-status::
-	Show only names and status of changed files. See the description
+	Show only the name(s) and status of each changed file. See the description
 	of the `--diff-filter` option on what the status letters mean.
 	Just like `--name-only` the file names are often encoded in UTF-8.

-- 
2.45.1-204-gd8ab1d464d