Merge branch 'en/merge-restore-to-pristine'

When "git merge" finds that it cannot perform a merge, it should
restore the working tree to the state before the command was
initiated, but in some corner cases it didn't.

* en/merge-restore-to-pristine:
  merge: do not exit restore_state() prematurely
  merge: ensure we can actually restore pre-merge state
  merge: make restore_state() restore staged state too
  merge: fix save_state() to work when there are stat-dirty files
  merge: do not abort early if one strategy fails to handle the merge
  merge: abort if index does not match HEAD for trivial merges
  merge-resolve: abort if index does not match HEAD
  merge-ort-wrappers: make printed message match the one from recursive

1 files changed, 43 insertions, 14 deletions

diff --git a/builtin/merge.c b/builtin/merge.c
index 23170f2d2a..f7c92c0e64 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -313,8 +313,16 @@ static int save_state(struct object_id *stash)
 	int len;
 	struct child_process cp = CHILD_PROCESS_INIT;
 	struct strbuf buffer = STRBUF_INIT;
+	struct lock_file lock_file = LOCK_INIT;
+	int fd;
 	int rc = -1;
 
+	fd = repo_hold_locked_index(the_repository, &lock_file, 0);
+	refresh_cache(REFRESH_QUIET);
+	if (0 <= fd)
+		repo_update_index_if_able(the_repository, &lock_file);
+	rollback_lock_file(&lock_file);
+
 	strvec_pushl(&cp.args, "stash", "create", NULL);
 	cp.out = -1;
 	cp.git_cmd = 1;
@@ -375,22 +383,26 @@ static void reset_hard(const struct object_id *oid, int verbose)
 static void restore_state(const struct object_id *head,
 			  const struct object_id *stash)
 {
-	const char *args[] = { "stash", "apply", NULL, NULL };
-
-	if (is_null_oid(stash))
-		return;
+	struct strvec args = STRVEC_INIT;
 
 	reset_hard(head, 1);
 
-	args[2] = oid_to_hex(stash);
+	if (is_null_oid(stash))
+		goto refresh_cache;
+
+	strvec_pushl(&args, "stash", "apply", "--index", "--quiet", NULL);
+	strvec_push(&args, oid_to_hex(stash));
 
 	/*
 	 * It is OK to ignore error here, for example when there was
 	 * nothing to restore.
 	 */
-	run_command_v_opt(args, RUN_GIT_CMD);
+	run_command_v_opt(args.v, RUN_GIT_CMD);
+	strvec_clear(&args);
 
-	refresh_cache(REFRESH_QUIET);
+refresh_cache:
+	if (discard_cache() < 0 || read_cache() < 0)
+		die(_("could not read index"));
 }
 
 /* This is called when no merge was necessary. */
@@ -754,8 +766,10 @@ static int try_merge_strategy(const char *strategy, struct commit_list *common,
 		else
 			clean = merge_recursive(&o, head, remoteheads->item,
 						reversed, &result);
-		if (clean < 0)
-			exit(128);
+		if (clean < 0) {
+			rollback_lock_file(&lock);
+			return 2;
+		}
 		if (write_locked_index(&the_index, &lock,
 				       COMMIT_LOCK | SKIP_IF_UNCHANGED))
 			die(_("unable to write %s"), get_index_file());
@@ -1599,6 +1613,21 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		 */
 		refresh_cache(REFRESH_QUIET);
 		if (allow_trivial && fast_forward != FF_ONLY) {
+			/*
+			 * Must first ensure that index matches HEAD before
+			 * attempting a trivial merge.
+			 */
+			struct tree *head_tree = get_commit_tree(head_commit);
+			struct strbuf sb = STRBUF_INIT;
+
+			if (repo_index_has_changes(the_repository, head_tree,
+						   &sb)) {
+				error(_("Your local changes to the following files would be overwritten by merge:\n  %s"),
+				      sb.buf);
+				strbuf_release(&sb);
+				return 2;
+			}
+
 			/* See if it is really trivial. */
 			git_committer_info(IDENT_STRICT);
 			printf(_("Trying really trivial in-index merge...\n"));
@@ -1655,12 +1684,12 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	 * tree in the index -- this means that the index must be in
 	 * sync with the head commit.  The strategies are responsible
 	 * to ensure this.
+	 *
+	 * Stash away the local changes so that we can try more than one
+	 * and/or recover from merge strategies bailing while leaving the
+	 * index and working tree polluted.
 	 */
-	if (use_strategies_nr == 1 ||
-	    /*
-	     * Stash away the local changes so that we can try more than one.
-	     */
-	    save_state(&stash))
+	if (save_state(&stash))
 		oidclr(&stash);
 
 	for (i = 0; !merge_was_ok && i < use_strategies_nr; i++) {