Re: [PATCH] git-commit: Allow to amend a merge commit that does not change the tree

[Junio C Hamano <gitster@pobox.com>]

Johannes Sixt <johannes.sixt@telecom.at> writes:

> 	I haven't gotten around to write a test case for this scenario,
> 	so I'm sending out the fix alone, in order to draw attention
> 	to the issue and have builtin-commit fixed by its authors, if
> 	necessary ;)

Untested but something like this ought to do.

 builtin-commit.c |   11 ++++++++++-
 1 files changed, 10 insertions(+), 1 deletions(-)

diff --git a/builtin-commit.c b/builtin-commit.c
index f37a90f..6c2dc39 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -676,6 +676,14 @@ int git_commit_config(const char *k, const char *v)
 	return git_status_config(k, v);
 }
 
+static int is_a_merge(const unsigned char *sha1)
+{
+	struct commit *commit = lookup_commit(sha1);
+	if (!commit || parse_commit(commit))
+		die("could not parse HEAD commit");
+	return !!(commit->parents && commit->parents->next);
+}
+
 static const char commit_utf8_warn[] =
 "Warning: commit message does not conform to UTF-8.\n"
 "You may want to amend it after fixing the message, or set the config\n"
@@ -701,7 +709,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		return 1;
 	}
 
-	if (!prepare_log_message(index_file, prefix) && !in_merge) {
+	if (!prepare_log_message(index_file, prefix) && !in_merge &&
+	    !(amend && is_a_merge(head_sha1))) {
 		run_status(stdout, index_file, prefix);
 		rollback_index_files();
 		unlink(commit_editmsg);