Make git-diff-tree indicate when it flushes

There are times when gitk needs to know that the commits it has sent
to git-diff-tree --stdin did not match, and it needs to know in a
timely fashion even if none of them match.  At the moment,
git-diff-tree outputs nothing for non-matching commits, so it is
impossible for gitk to distinguish between git-diff-tree being slow
and git-diff-tree saying no.

This makes git-diff-tree flush its output and echo back the
input line when it is not a valid-looking object name.  Gitk, or
other users of git-diff-tree --stdin, can use a blank line or
any other "marker line" to indicate that git-diff-tree has
processed all the commits on its input up to the echoed back
marker line, and any commits that have not been output do not
match.

[jc: re-done after a couple of back-and-forth discussion on the list.]

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

diff --git a/builtin-diff-tree.c b/builtin-diff-tree.c
index cc53b81..58cf658 100644 (file)
--- a/builtin-diff-tree.c
+++ b/builtin-diff-tree.c
@@ -138,11 +138,15 @@ int cmd_diff_tree(int argc, const char **argv, char **envp)
        if (opt->diffopt.detect_rename)
                opt->diffopt.setup |= (DIFF_SETUP_USE_SIZE_CACHE |
                                       DIFF_SETUP_USE_CACHE);
-       while (fgets(line, sizeof(line), stdin))
-               if (line[0] == '\n')
+       while (fgets(line, sizeof(line), stdin)) {
+               unsigned char sha1[20];
+
+               if (get_sha1_hex(line, sha1)) {
+                       fputs(line, stdout);
                        fflush(stdout);
+               }
                else
                        diff_tree_stdin(line);
-
+       }
        return 0;
 }