[PATCH 2/2] builtin/stash: merge index in-core

@@ -422,50 +422,6 @@ static int create_index_from_tree(const struct object_id *tree_id,
 	return ret;
 }
 
-static int diff_tree_binary(struct strbuf *out, struct object_id *w_commit)
-{
-	struct child_process cp = CHILD_PROCESS_INIT;
-	const char *w_commit_hex = oid_to_hex(w_commit);
-
-	/*
-	 * Diff-tree would not be very hard to replace with a native function,
-	 * however it should be done together with apply_cached.
-	 */
-	cp.git_cmd = 1;
-	strvec_pushl(&cp.args, "diff-tree", "--binary", "--no-color", NULL);
-	strvec_pushf(&cp.args, "%s^2^..%s^2", w_commit_hex, w_commit_hex);
-
-	return pipe_command(&cp, NULL, 0, out, 0, NULL, 0);
-}
-
-static int apply_cached(struct strbuf *out)
-{
-	struct child_process cp = CHILD_PROCESS_INIT;
-
-	/*
-	 * Apply currently only reads either from stdin or a file, thus
-	 * apply_all_patches would have to be updated to optionally take a
-	 * buffer.
-	 */
-	cp.git_cmd = 1;
-	strvec_pushl(&cp.args, "apply", "--cached", NULL);
-	return pipe_command(&cp, out->buf, out->len, NULL, 0, NULL, 0);
-}
-
-static int reset_head(void)
-{
-	struct child_process cp = CHILD_PROCESS_INIT;
-
-	/*
-	 * Reset is overall quite simple, however there is no current public
-	 * API for resetting.
-	 */
-	cp.git_cmd = 1;
-	strvec_pushl(&cp.args, "reset", "--quiet", "--refresh", NULL);
-
-	return run_command(&cp);
-}
-
 static int is_path_a_directory(const char *path)
 {
 	/*

@@ -669,29 +625,25 @@ static enum stash_apply_result do_apply_stash(const char *prefix,
 		    oideq(&c_tree, &info->i_tree)) {
 			has_index = 0;
 		} else {
-			struct strbuf out = STRBUF_INIT;
+			struct merge_result result = { 0 };
 
-			if (diff_tree_binary(&out, &info->w_commit)) {
-				strbuf_release(&out);
-				return error(_("could not generate diff %s^!."),
-					     oid_to_hex(&info->w_commit));
-			}
+			init_basic_merge_options(&o, the_repository);
 
-			ret = apply_cached(&out);
-			strbuf_release(&out);
-			if (ret)
+			o.verbosity = 0;
+
+			head = lookup_tree(o.repo, &c_tree);
+			merge = lookup_tree(o.repo, &info->i_tree);
+			merge_base = lookup_tree(o.repo, &info->b_tree);
+
+			merge_incore_nonrecursive(&o, head, merge, merge_base,
+						  &result);
+
+			if (!result.clean)
 				return error(_("conflicts in index. "
 					       "Try without --index."));
 
-			discard_index(the_repository->index);
-			repo_read_index(the_repository);
-			if (write_index_as_tree(&index_tree, the_repository->index,
-						repo_get_index_file(the_repository), 0, NULL))
-				return error(_("could not save index tree"));
-
-			reset_head();
-			discard_index(the_repository->index);
-			repo_read_index(the_repository);
+			oidcpy(&index_tree, &result.tree->object.oid);
+			clear_merge_options(&o);
 		}
 	}
 

@@ -5035,8 +5035,6 @@ static void merge_start(struct merge_options *opt, struct merge_result *result)
 	trace2_region_enter("merge", "sanity checks", opt->repo);
 	assert(opt->repo);
 
-	assert(opt->branch1 && opt->branch2);
-
 	assert(opt->detect_directory_renames >= MERGE_DIRECTORY_RENAMES_NONE &&
 	       opt->detect_directory_renames <= MERGE_DIRECTORY_RENAMES_TRUE);
 	assert(opt->rename_limit >= -1);

@@ -5409,7 +5407,6 @@ void merge_incore_nonrecursive(struct merge_options *opt,
 	trace2_region_enter("merge", "incore_nonrecursive", opt->repo);
 
 	trace2_region_enter("merge", "merge_start", opt->repo);
-	assert(opt->ancestor != NULL);
 	merge_check_renames_reusable(opt, result, merge_base, side1, side2);
 	merge_start(opt, result);
 	/*

@@ -801,6 +801,15 @@ verify_no_mergehead () {
 	test_cmp result.1-5 file
 '
 
+test_expect_success 'fast-forward merge with --autostash, stash.index' '
+	git reset --hard c0 &&
+	git stash clear &&
+	echo staged >>z && git add z &&
+	git -c stash.index=true merge --autostash c1 2>err &&
+	test_grep "Applied autostash." err &&
+	test_stdout_line_count = 0 git stash list
+'
+
 test_expect_success 'failed fast-forward merge with --autostash' '
 	git reset --hard c0 &&
 	git merge-file file file.orig file.5 &&