Be more user-friendly when refusing to do something because of conflict.

Various commands refuse to run in the presence of conflicts (commit,
merge, pull, cherry-pick/revert). They all used to provide rough, and
inconsistant error messages.

A new variable advice.resolveconflict is introduced, and allows more
verbose messages, pointing the user to the appropriate solution.

For commit, the error message used to look like this:

$ git commit
foo.txt: needs merge
foo.txt: unmerged (c34a92682e0394bc0d6f4d4a67a8e2d32395c169)
foo.txt: unmerged (3afcd75de8de0bb5076942fcb17446be50451030)
foo.txt: unmerged (c9785d77b76dfe4fb038bf927ee518f6ae45ede4)
error: Error building trees

The "need merge" line is given by refresh_cache. We add the IN_PORCELAIN
option to make the output more consistant with the other porcelain
commands, and catch the error in return, to stop with a clean error
message. The next lines were displayed by a call to cache_tree_update(),
which is not reached anymore if we noticed the conflict.

The new output looks like:

U       foo.txt
fatal: 'commit' is not possible because you have unmerged files.
Please, fix them up in the work tree, and then use 'git add/rm <file>' as
appropriate to mark resolution and make a commit, or use 'git commit -a'.

Pull is slightly modified to abort immediately if $GIT_DIR/MERGE_HEAD
exists instead of waiting for merge to complain.

The behavior of merge and the test-case are slightly modified to reflect
the usual flow: start with conflicts, fix them, and afterwards get rid of
MERGE_HEAD, with different error messages at each stage.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/builtin-commit.c b/builtin-commit.c
index f54772f74..c58712c53 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -219,6 +219,16 @@ static void create_base_index(void)
 		exit(128); /* We've already reported the error, finish dying */
 }
 
+static void refresh_cache_or_die(int refresh_flags)
+{
+	/*
+	 * refresh_flags contains REFRESH_QUIET, so the only errors
+	 * are for unmerged entries.
+	 */
+	if (refresh_cache(refresh_flags | REFRESH_IN_PORCELAIN))
+		die_resolve_conflict("commit");
+}
+
 static char *prepare_index(int argc, const char **argv, const char *prefix, int is_status)
 {
 	int fd;
@@ -258,7 +268,7 @@ static char *prepare_index(int argc, const char **argv, const char *prefix, int
 	if (all || (also && pathspec && *pathspec)) {
 		int fd = hold_locked_index(&index_lock, 1);
 		add_files_to_cache(also ? prefix : NULL, pathspec, 0);
-		refresh_cache(refresh_flags);
+		refresh_cache_or_die(refresh_flags);
 		if (write_cache(fd, active_cache, active_nr) ||
 		    close_lock_file(&index_lock))
 			die("unable to write new_index file");
@@ -277,7 +287,7 @@ static char *prepare_index(int argc, const char **argv, const char *prefix, int
 	 */
 	if (!pathspec || !*pathspec) {
 		fd = hold_locked_index(&index_lock, 1);
-		refresh_cache(refresh_flags);
+		refresh_cache_or_die(refresh_flags);
 		if (write_cache(fd, active_cache, active_nr) ||
 		    commit_locked_index(&index_lock))
 			die("unable to write new_index file");