builtin/diff: update usage comment

A comment in cmd_diff() states that if one tree-ish and no blobs are
provided, (the "N=1, M=0" case), it will provide a diff between the tree
and the cache. This is incorrect because a diff happens between the
tree-ish and the working tree. Remove the `--cached` in the comment so
that the correct behavior is shown. Add a new section describing the
"N=1, M=0, --cached" behavior.

Next, describe the "N=0, M=0, --cached" case, similar to the above since
it is undocumented.

Finally, fix some spacing issues. Add spaces between each section for
consistency and readability. Also, change tabs within the comment into
spaces.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/diff.c b/builtin/diff.c
index 42ac803091e6a0c7e22203b097d1f0001c9f5302..bdae4d6a58e0ed82e56e4c6faa6d7c46e2663e2c 100644 (file)
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -266,18 +266,30 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 
        /*
         * We could get N tree-ish in the rev.pending_objects list.
-        * Also there could be M blobs there, and P pathspecs.
+        * Also there could be M blobs there, and P pathspecs. --cached may
+        * also be present.
         *
         * N=0, M=0:
-        *      cache vs files (diff-files)
+        *      cache vs files (diff-files)
+        *
+        * N=0, M=0, --cached:
+        *      HEAD vs cache (diff-index --cached)
+        *
         * N=0, M=2:
         *      compare two random blobs.  P must be zero.
+        *
         * N=0, M=1, P=1:
-        *      compare a blob with a working tree file.
+        *      compare a blob with a working tree file.
+        *
+        * N=1, M=0:
+        *      tree vs files (diff-index)
         *
         * N=1, M=0:
         *      tree vs cache (diff-index --cached)
         *
+        * N=1, M=0, --cached:
+        *      tree vs files (diff-index)
+        *
         * N=2, M=0:
         *      tree vs tree (diff-tree)
         *