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

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++) {

git-merge-resolve.sh

@@ -5,6 +5,16 @@
 #
 # Resolve two trees, using enhanced multi-base read-tree.
 
+. git-sh-setup
+
+# Abort if index does not match HEAD
+if ! git diff-index --quiet --cached HEAD --
+then
+    gettextln "Error: Your local changes to the following files would be overwritten by merge"
+    git diff-index --cached --name-only HEAD -- | sed -e 's/^/    /'
+    exit 2
+fi
+
 # The first parameters up to -- are merge bases; the rest are heads.
 bases= head= remotes= sep_seen=
 for arg

merge-ort-wrappers.c

@@ -10,8 +10,8 @@ static int unclean(struct merge_options *opt, struct tree *head)
 	struct strbuf sb = STRBUF_INIT;
 
 	if (head && repo_index_has_changes(opt->repo, head, &sb)) {
-		fprintf(stderr, _("Your local changes to the following files would be overwritten by merge:\n  %s"),
-		    sb.buf);
+		error(_("Your local changes to the following files would be overwritten by merge:\n  %s"),
+		      sb.buf);
 		strbuf_release(&sb);
 		return -1;
 	}

t/t6402-merge-rename.sh

@@ -210,7 +210,7 @@ test_expect_success 'updated working tree file should prevent the merge' '
 	echo >>M one line addition &&
 	cat M >M.saved &&
 	git update-index M &&
-	test_expect_code 128 git pull --no-rebase . yellow &&
+	test_expect_code 2 git pull --no-rebase . yellow &&
 	test_cmp M M.saved &&
 	rm -f M.saved
 '

t/t6424-merge-unrelated-index-changes.sh

@@ -114,6 +114,39 @@ test_expect_success 'resolve, non-trivial' '
 	test_path_is_missing .git/MERGE_HEAD
 '
 
+test_expect_success 'resolve, trivial, related file removed' '
+	git reset --hard &&
+	git checkout B^0 &&
+
+	git rm a &&
+	test_path_is_missing a &&
+
+	test_must_fail git merge -s resolve C^0 &&
+
+	test_path_is_missing a &&
+	test_path_is_missing .git/MERGE_HEAD
+'
+
+test_expect_success 'resolve, non-trivial, related file removed' '
+	git reset --hard &&
+	git checkout B^0 &&
+
+	git rm a &&
+	test_path_is_missing a &&
+
+	# We also ask for recursive in order to turn off the "allow_trivial"
+	# setting in builtin/merge.c, and ensure that resolve really does
+	# correctly fail the merge (I guess this also tests that recursive
+	# correctly fails the merge, but the main thing we are attempting
+	# to test here is resolve and are just using the side effect of
+	# adding recursive to ensure that resolve is actually tested rather
+	# than the trivial merge codepath)
+	test_must_fail git merge -s resolve -s recursive D^0 &&
+
+	test_path_is_missing a &&
+	test_path_is_missing .git/MERGE_HEAD
+'
+
 test_expect_success 'recursive' '
 	git reset --hard &&
 	git checkout B^0 &&
@@ -242,4 +275,36 @@ test_expect_success 'subtree' '
 	test_path_is_missing .git/MERGE_HEAD
 '
 
+test_expect_success 'avoid failure due to stat-dirty files' '
+	git reset --hard &&
+	git checkout B^0 &&
+
+	# Make "a" be stat-dirty
+	test-tool chmtime =+1 a &&
+
+	# stat-dirty file should not prevent stash creation in builtin/merge.c
+	git merge -s resolve -s recursive D^0
+'
+
+test_expect_success 'with multiple strategies, recursive or ort failure do not early abort' '
+	git reset --hard &&
+	git checkout B^0 &&
+
+	test_seq 0 10 >a &&
+	git add a &&
+	git rev-parse :a >expect &&
+
+	sane_unset GIT_TEST_MERGE_ALGORITHM &&
+	test_must_fail git merge -s recursive -s ort -s octopus C^0 >output 2>&1 &&
+
+	grep "Trying merge strategy recursive..." output &&
+	grep "Trying merge strategy ort..." output &&
+	grep "Trying merge strategy octopus..." output &&
+	grep "No merge strategy handled the merge." output &&
+
+	# Changes to "a" should remain staged
+	git rev-parse :a >actual &&
+	test_cmp expect actual
+'
+
 test_done

t/t6439-merge-co-error-msgs.sh

@@ -47,6 +47,7 @@ test_expect_success 'untracked files overwritten by merge (fast and non-fast for
 		export GIT_MERGE_VERBOSITY &&
 		test_must_fail git merge branch 2>out2
 	) &&
+	echo "Merge with strategy ${GIT_TEST_MERGE_ALGORITHM:-ort} failed." >>expect &&
 	test_cmp out2 expect &&
 	git reset --hard HEAD^
 '

t/t7607-merge-state.sh

@@ -0,0 +1,32 @@
+#!/bin/sh
+
+test_description="Test that merge state is as expected after failed merge"
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+. ./test-lib.sh
+
+test_expect_success 'Ensure we restore original state if no merge strategy handles it' '
+	test_commit --no-tag "Initial" base base &&
+
+	for b in branch1 branch2 branch3
+	do
+		git checkout -b $b main &&
+		test_commit --no-tag "Change on $b" base $b || return 1
+	done &&
+
+	git checkout branch1 &&
+	# This is a merge that octopus cannot handle.  Note, that it does not
+	# just hit conflicts, it completely fails and says that it cannot
+	# handle this type of merge.
+	test_expect_code 2 git merge branch2 branch3 >output 2>&1 &&
+	grep "fatal: merge program failed" output &&
+	grep "Should not be doing an octopus" output &&
+
+	# Make sure we did not leave stray changes around when no appropriate
+	# merge strategy was found
+	git diff --exit-code --name-status &&
+	test_path_is_missing .git/MERGE_HEAD
+'
+
+test_done