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builtin-commit: use reduce_heads() only when appropriate

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Since commit 6bb6b034 (builtin-commit: use commit_tree(), 2008-09-10),
builtin-commit performs a reduce_heads() unconditionally.  However,
it's not always needed, and in some cases even harmful.

reduce_heads() is not needed for the initial commit or for an
"ordinary" commit, because they don't have any or have only one
parent, respectively.

reduce_heads() must be avoided when 'git commit' is run after a 'git
merge --no-ff --no-commit', otherwise it will turn the
non-fast-forward merge into fast-forward.  For the same reason,
reduce_heads() must be avoided when amending such a merge commit.

To resolve this issue, 'git merge' will write info about whether
fast-forward is allowed or not to $GIT_DIR/MERGE_MODE.  Based on this
info, 'git commit' will only perform reduce_heads() when it's
committing a merge and fast-forward is enabled.

Also add test cases to ensure that non-fast-forward merges are
committed and amended properly.

Signed-off-by: Miklos Vajna <vmiklos@frugalware.org>
Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
This commit is contained in:
Miklos Vajna
2008-10-03 14:04:47 +02:00
committed by Shawn O. Pearce
parent 52e8370bc7
commit cf10f9fdd5
4 changed files with 41 additions and 2 deletions
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10
builtin-merge.c
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@ -180,6 +180,7 @@ static void drop_save(void)
{
unlink(git_path("MERGE_HEAD"));
unlink(git_path("MERGE_MSG"));
unlink(git_path("MERGE_MODE"));
}
static void save_state(void)
@ -1210,6 +1211,15 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
merge_msg.len)
die("Could not write to %s", git_path("MERGE_MSG"));
close(fd);
fd = open(git_path("MERGE_MODE"), O_WRONLY | O_CREAT | O_TRUNC, 0666);
if (fd < 0)
die("Could open %s for writing", git_path("MERGE_MODE"));
strbuf_reset(&buf);
if (!allow_fast_forward)
strbuf_addf(&buf, "no-ff");
if (write_in_full(fd, buf.buf, buf.len) != buf.len)
die("Could not write to %s", git_path("MERGE_MODE"));
close(fd);
}
if (merge_was_ok) {