Merge branch 'en/merge-tree-check'

"git merge-tree" learned an option to see if it resolves cleanly
without actually creating a result.

* en/merge-tree-check:
  merge-tree: add a new --quiet flag
  merge-ort: add a new mergeability_only option

Documentation/git-merge-tree.adoc

@@ -65,6 +65,12 @@ OPTIONS
 	default is to include these messages if there are merge
 	conflicts, and to omit them otherwise.
 
+--quiet::
+	Disable all output from the program.  Useful when you are only
+	interested in the exit status.  Allows merge-tree to exit
+	early when it finds a conflict, and allows it to avoid writing
+	most objects created by merges.
+
 --allow-unrelated-histories::
 	merge-tree will by default error out if the two branches specified
 	share no common history.  This flag can be given to override that

builtin/merge-tree.c

@@ -490,6 +490,9 @@ static int real_merge(struct merge_tree_options *o,
 	if (result.clean < 0)
 		die(_("failure to merge"));
 
+	if (o->merge_options.mergeability_only)
+		goto cleanup;
+
 	if (show_messages == -1)
 		show_messages = !result.clean;
 
@@ -522,6 +525,8 @@ static int real_merge(struct merge_tree_options *o,
 	}
 	if (o->use_stdin)
 		putchar(line_termination);
+
+cleanup:
 	merge_finalize(&opt, &result);
 	clear_merge_options(&opt);
 	return !result.clean; /* result.clean < 0 handled above */
@@ -538,6 +543,7 @@ int cmd_merge_tree(int argc,
 	int original_argc;
 	const char *merge_base = NULL;
 	int ret;
+	int quiet = 0;
 
 	const char * const merge_tree_usage[] = {
 		N_("git merge-tree [--write-tree] [<options>] <branch1> <branch2>"),
@@ -552,6 +558,10 @@ int cmd_merge_tree(int argc,
 			    N_("do a trivial merge only"), MODE_TRIVIAL),
 		OPT_BOOL(0, "messages", &o.show_messages,
 			 N_("also show informational/conflict messages")),
+		OPT_BOOL_F(0, "quiet",
+			   &quiet,
+			   N_("suppress all output; only exit status wanted"),
+			   PARSE_OPT_NONEG),
 		OPT_SET_INT('z', NULL, &line_termination,
 			    N_("separate paths with the NUL character"), '\0'),
 		OPT_BOOL_F(0, "name-only",
@@ -583,6 +593,14 @@ int cmd_merge_tree(int argc,
 	argc = parse_options(argc, argv, prefix, mt_options,
 			     merge_tree_usage, PARSE_OPT_STOP_AT_NON_OPTION);
 
+	if (quiet && o.show_messages == -1)
+		o.show_messages = 0;
+	o.merge_options.mergeability_only = quiet;
+	die_for_incompatible_opt2(quiet, "--quiet", o.show_messages, "--messages");
+	die_for_incompatible_opt2(quiet, "--quiet", o.name_only, "--name-only");
+	die_for_incompatible_opt2(quiet, "--quiet", o.use_stdin, "--stdin");
+	die_for_incompatible_opt2(quiet, "--quiet", !line_termination, "-z");
+
 	if (xopts.nr && o.mode == MODE_TRIVIAL)
 		die(_("--trivial-merge is incompatible with all other options"));
 	for (size_t x = 0; x < xopts.nr; x++)

merge-ort.c

@@ -2127,6 +2127,7 @@ static int handle_content_merge(struct merge_options *opt,
 				const struct version_info *b,
 				const char *pathnames[3],
 				const int extra_marker_size,
+				const int record_object,
 				struct version_info *result)
 {
 	/*
@@ -2214,7 +2215,7 @@ static int handle_content_merge(struct merge_options *opt,
 			ret = -1;
 		}
 
-		if (!ret &&
+		if (!ret && record_object &&
 		    write_object_file(result_buf.ptr, result_buf.size,
 				      OBJ_BLOB, &result->oid)) {
 			path_msg(opt, ERROR_OBJECT_WRITE_FAILED, 0,
@@ -2897,6 +2898,7 @@ static int process_renames(struct merge_options *opt,
 			struct version_info merged;
 			struct conflict_info *base, *side1, *side2;
 			unsigned was_binary_blob = 0;
+			const int record_object = true;
 
 			pathnames[0] = oldpath;
 			pathnames[1] = newpath;
@@ -2947,6 +2949,7 @@ static int process_renames(struct merge_options *opt,
 							   &side2->stages[2],
 							   pathnames,
 							   1 + 2 * opt->priv->call_depth,
+							   record_object,
 							   &merged);
 			if (clean_merge < 0)
 				return -1;
@@ -3061,6 +3064,7 @@ static int process_renames(struct merge_options *opt,
 
 			struct conflict_info *base, *side1, *side2;
 			int clean;
+			const int record_object = true;
 
 			pathnames[0] = oldpath;
 			pathnames[other_source_index] = oldpath;
@@ -3080,6 +3084,7 @@ static int process_renames(struct merge_options *opt,
 						     &side2->stages[2],
 						     pathnames,
 						     1 + 2 * opt->priv->call_depth,
+						     record_object,
 						     &merged);
 			if (clean < 0)
 				return -1;
@@ -3931,9 +3936,12 @@ static int write_completed_directory(struct merge_options *opt,
 		 * Write out the tree to the git object directory, and also
 		 * record the mode and oid in dir_info->result.
 		 */
+		int record_tree = (!opt->mergeability_only ||
+				   opt->priv->call_depth);
 		dir_info->is_null = 0;
 		dir_info->result.mode = S_IFDIR;
-		if (write_tree(&dir_info->result.oid, &info->versions, offset,
+		if (record_tree &&
+		    write_tree(&dir_info->result.oid, &info->versions, offset,
 			       opt->repo->hash_algo->rawsz) < 0)
 			ret = -1;
 	}
@@ -4231,10 +4239,13 @@ static int process_entry(struct merge_options *opt,
 		struct version_info *o = &ci->stages[0];
 		struct version_info *a = &ci->stages[1];
 		struct version_info *b = &ci->stages[2];
+		int record_object = (!opt->mergeability_only ||
+				     opt->priv->call_depth);
 
 		clean_merge = handle_content_merge(opt, path, o, a, b,
 						   ci->pathnames,
 						   opt->priv->call_depth * 2,
+						   record_object,
 						   &merged_file);
 		if (clean_merge < 0)
 			return -1;
@@ -4395,6 +4406,8 @@ static int process_entries(struct merge_options *opt,
 						   STRING_LIST_INIT_NODUP,
 						   NULL, 0 };
 	int ret = 0;
+	const int record_tree = (!opt->mergeability_only ||
+				 opt->priv->call_depth);
 
 	trace2_region_enter("merge", "process_entries setup", opt->repo);
 	if (strmap_empty(&opt->priv->paths)) {
@@ -4454,6 +4467,12 @@ static int process_entries(struct merge_options *opt,
 				ret = -1;
 				goto cleanup;
 			};
+			if (!ci->merged.clean && opt->mergeability_only &&
+			    !opt->priv->call_depth) {
+				ret = 0;
+				goto cleanup;
+			}
+
 		}
 	}
 	trace2_region_leave("merge", "processing", opt->repo);
@@ -4468,7 +4487,8 @@ static int process_entries(struct merge_options *opt,
 		fflush(stdout);
 		BUG("dir_metadata accounting completely off; shouldn't happen");
 	}
-	if (write_tree(result_oid, &dir_metadata.versions, 0,
+	if (record_tree &&
+	    write_tree(result_oid, &dir_metadata.versions, 0,
 		       opt->repo->hash_algo->rawsz) < 0)
 		ret = -1;
 cleanup:
@@ -4715,6 +4735,8 @@ void merge_display_update_messages(struct merge_options *opt,
 
 	if (opt->record_conflict_msgs_as_headers)
 		BUG("Either display conflict messages or record them as headers, not both");
+	if (opt->mergeability_only)
+		BUG("Displaying conflict messages incompatible with mergeability-only checks");
 
 	trace2_region_enter("merge", "display messages", opt->repo);
 
@@ -5171,10 +5193,12 @@ redo:
 	result->path_messages = &opt->priv->conflicts;
 
 	if (result->clean >= 0) {
-		result->tree = parse_tree_indirect(&working_tree_oid);
-		if (!result->tree)
-			die(_("unable to read tree (%s)"),
-			    oid_to_hex(&working_tree_oid));
+		if (!opt->mergeability_only) {
+			result->tree = parse_tree_indirect(&working_tree_oid);
+			if (!result->tree)
+				die(_("unable to read tree (%s)"),
+				    oid_to_hex(&working_tree_oid));
+		}
 		/* existence of conflicted entries implies unclean */
 		result->clean &= strmap_empty(&opt->priv->conflicted);
 	}

merge-ort.h

@@ -83,6 +83,7 @@ struct merge_options {
 	/* miscellaneous control options */
 	const char *subtree_shift;
 	unsigned renormalize : 1;
+	unsigned mergeability_only : 1; /* exit early, write fewer objects */
 	unsigned record_conflict_msgs_as_headers : 1;
 	const char *msg_header_prefix;
 

t/t4301-merge-tree-write-tree.sh

@@ -54,6 +54,25 @@ test_expect_success setup '
 	git commit -m first-commit
 '
 
+test_expect_success '--quiet on clean merge' '
+	# Get rid of loose objects to start with
+	git gc &&
+	echo "0 objects, 0 kilobytes" >expect &&
+	git count-objects >actual &&
+	test_cmp expect actual &&
+
+	# Ensure merge is successful (exit code of 0)
+	git merge-tree --write-tree --quiet side1 side3 >output &&
+
+	# Ensure there is no output
+	test_must_be_empty output &&
+
+	# Ensure no loose objects written (all new objects written would have
+	# been in "outer layer" of the merge)
+	git count-objects >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'Clean merge' '
 	TREE_OID=$(git merge-tree --write-tree side1 side3) &&
 	q_to_tab <<-EOF >expect &&
@@ -72,6 +91,25 @@ test_expect_success 'Failed merge without rename detection' '
 	grep "CONFLICT (modify/delete): numbers deleted" out
 '
 
+test_expect_success  '--quiet on conflicted merge' '
+	# Get rid of loose objects to start with
+	git gc &&
+	echo "0 objects, 0 kilobytes" >expect &&
+	git count-objects >actual &&
+	test_cmp expect actual &&
+
+	# Ensure merge has conflict
+	test_expect_code 1 git merge-tree --write-tree --quiet side1 side2 >output &&
+
+	# Ensure there is no output
+	test_must_be_empty output &&
+
+	# Ensure no loose objects written (all new objects written would have
+	# been in "outer layer" of the merge)
+	git count-objects >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'Content merge and a few conflicts' '
 	git checkout side1^0 &&
 	test_must_fail git merge side2 &&