[PATCH v4 0/2] merge-tree: add new --quiet option

Changes since v3:

 * Renamed --dry-run -> --quiet . Any further naming suggestions?

Changes since v2:

 * Converted locations missed in v1 in changing --mergeability-only ->
   --dry-run

Changes since v1:

 * Renamed --mergeability-only flag to --dry-run, as per suggestion from
   Junio
 * added some commit message clarifications

This adds a new flag, --dry-run, to git merge-tree, which suppresses all output and leaves only the exit status (reflecting successful merge or conflict). This is useful for Git Forges in cases where they are only interested in whether two branches can be merged, without needing the actual merge result or conflict details.

The advantage of the flag is two fold:

 * The merge machinery can exit once it detects a conflict, instead of
   continuing to compute merge result information
 * The merge machinery can avoid writing merged blobs and trees to the
   object store when in the outer layer of the merging process (more details
   in the first commit message).

Elijah Newren (2):
  merge-ort: add a new mergeability_only option
  merge-tree: add a new --quiet flag

 Documentation/git-merge-tree.adoc |  6 +++++
 builtin/merge-tree.c              | 18 +++++++++++++++
 merge-ort.c                       | 38 +++++++++++++++++++++++++------
 merge-ort.h                       |  1 +
 t/t4301-merge-tree-write-tree.sh  | 38 +++++++++++++++++++++++++++++++
 5 files changed, 94 insertions(+), 7 deletions(-)

base-commit: 6c0bd1fc70efaf053abe4e57c976afdc72d15377
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1920%2Fnewren%2Fmergeability-only-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1920/newren/mergeability-only-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/1920

Range-diff vs v3:

 1:  4757c4810d3 = 1:  4757c4810d3 merge-ort: add a new mergeability_only option
 2:  f11824317a8 ! 2:  7c40d3c9216 merge-tree: add a new --dry-run flag
     @@ Metadata
      Author: Elijah Newren <newren@gmail.com>
      
       ## Commit message ##
     -    merge-tree: add a new --dry-run flag
     +    merge-tree: add a new --quiet flag
      
          Git Forges may be interested in whether two branches can be merged while
          not being interested in what the resulting merge tree is nor which files
     -    conflicted.  For such cases, add a new --dry-run flag which
     +    conflicted.  For such cases, add a new --quiet flag which
          will make use of the new mergeability_only flag added to merge-ort in
          the previous commit.  This option allows the merge machinery to, in the
          outer layer of the merge:
     @@ Documentation/git-merge-tree.adoc: OPTIONS
       	default is to include these messages if there are merge
       	conflicts, and to omit them otherwise.
       
     -+--dry-run::
     ++--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
     @@ builtin/merge-tree.c: int cmd_merge_tree(int argc,
       	int original_argc;
       	const char *merge_base = NULL;
       	int ret;
     -+	int dry_run = 0;
     ++	int quiet = 0;
       
       	const char * const merge_tree_usage[] = {
       		N_("git merge-tree [--write-tree] [<options>] <branch1> <branch2>"),
     @@ builtin/merge-tree.c: 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, "dry-run",
     -+			   &dry_run,
     ++		OPT_BOOL_F(0, "quiet",
     ++			   &quiet,
      +			   N_("suppress all output; only exit status wanted"),
      +			   PARSE_OPT_NONEG),
       		OPT_SET_INT('z', NULL, &line_termination,
     @@ builtin/merge-tree.c: int cmd_merge_tree(int argc,
       	argc = parse_options(argc, argv, prefix, mt_options,
       			     merge_tree_usage, PARSE_OPT_STOP_AT_NON_OPTION);
       
     -+	if (dry_run && o.show_messages == -1)
     ++	if (quiet && o.show_messages == -1)
      +		o.show_messages = 0;
     -+	o.merge_options.mergeability_only = dry_run;
     -+	die_for_incompatible_opt2(dry_run, "--dry-run",
     -+				  o.show_messages, "--messages");
     -+	die_for_incompatible_opt2(dry_run, "--dry-run",
     -+				  o.name_only, "--name-only");
     -+	die_for_incompatible_opt2(dry_run, "--dry-run",
     -+				  o.use_stdin, "--stdin");
     -+	die_for_incompatible_opt2(dry_run, "--dry-run",
     -+				  !line_termination, "-z");
     ++	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"));
     @@ t/t4301-merge-tree-write-tree.sh: test_expect_success setup '
       	git commit -m first-commit
       '
       
     -+test_expect_success '--dry-run on clean merge' '
     ++test_expect_success '--quiet on clean merge' '
      +	# Get rid of loose objects to start with
      +	git gc &&
      +	echo "0 objects, 0 kilobytes" >expect &&
     @@ t/t4301-merge-tree-write-tree.sh: test_expect_success setup '
      +	test_cmp expect actual &&
      +
      +	# Ensure merge is successful (exit code of 0)
     -+	git merge-tree --write-tree --dry-run side1 side3 >output &&
     ++	git merge-tree --write-tree --quiet side1 side3 >output &&
      +
      +	# Ensure there is no output
      +	test_must_be_empty output &&
     @@ t/t4301-merge-tree-write-tree.sh: test_expect_success 'Failed merge without rena
       	grep "CONFLICT (modify/delete): numbers deleted" out
       '
       
     -+test_expect_success  '--dry-run on conflicted merge' '
     ++test_expect_success  '--quiet on conflicted merge' '
      +	# Get rid of loose objects to start with
      +	git gc &&
      +	echo "0 objects, 0 kilobytes" >expect &&
     @@ t/t4301-merge-tree-write-tree.sh: test_expect_success 'Failed merge without rena
      +	test_cmp expect actual &&
      +
      +	# Ensure merge has conflict
     -+	test_expect_code 1 git merge-tree --write-tree --dry-run side1 side2 >output &&
     ++	test_expect_code 1 git merge-tree --write-tree --quiet side1 side2 >output &&
      +
      +	# Ensure there is no output
      +	test_must_be_empty output &&