builtin: add new "history" command

When rewriting history via git-rebase(1) there are a few very common use
cases:

  - The ordering of two commits should be reversed.

  - A commit should be split up into two commits.

  - A commit should be dropped from the history completely.

  - Multiple commits should be squashed into one.

  - Editing an existing commit that is not the tip of the current
    branch.

While these operations are all doable, it often feels needlessly kludgey
to do so by doing an interactive rebase, using the editor to say what
one wants, and then perform the actions. Furthermore, some operations
like splitting up a commit into two are way more involved than that and
require a whole series of commands.

Add a new "history" command to plug this gap. This command will have
several different subcommands to imperatively rewrite history for common
use cases like the above. Some of these subcommands will be implemented
in subsequent commits.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitignore

@@ -79,6 +79,7 @@
 /git-grep
 /git-hash-object
 /git-help
+/git-history
 /git-hook
 /git-http-backend
 /git-http-fetch

Documentation/git-history.adoc

@@ -0,0 +1,42 @@
+git-history(1)
+==============
+
+NAME
+----
+git-history - EXPERIMENTAL: Rewrite history of the current branch
+
+SYNOPSIS
+--------
+[synopsis]
+git history [<options>]
+
+DESCRIPTION
+-----------
+
+Rewrite history by rearranging or modifying specific commits in the
+history.
+
+THIS COMMAND IS EXPERIMENTAL. THE BEHAVIOR MAY CHANGE.
+
+This command is related to linkgit:git-rebase[1] in that both commands can be
+used to rewrite history. You should use rebases if you want to reapply a range
+of commits onto a different base, or interactive rebases if you want to edit a
+range of commits.
+
+Note that this command does not (yet) work with histories that contain
+merges. You should use linkgit:git-rebase[1] with the `--rebase-merges`
+flag instead.
+
+COMMANDS
+--------
+
+Several commands are available to rewrite history in different ways:
+
+CONFIGURATION
+-------------
+
+include::includes/cmd-config-section-all.adoc[]
+
+GIT
+---
+Part of the linkgit:git[1] suite

Documentation/meson.build

@@ -64,6 +64,7 @@ manpages = {
   'git-gui.adoc' : 1,
   'git-hash-object.adoc' : 1,
   'git-help.adoc' : 1,
+  'git-history.adoc' : 1,
   'git-hook.adoc' : 1,
   'git-http-backend.adoc' : 1,
   'git-http-fetch.adoc' : 1,

Makefile

@@ -1408,6 +1408,7 @@ BUILTIN_OBJS += builtin/get-tar-commit-id.o
 BUILTIN_OBJS += builtin/grep.o
 BUILTIN_OBJS += builtin/hash-object.o
 BUILTIN_OBJS += builtin/help.o
+BUILTIN_OBJS += builtin/history.o
 BUILTIN_OBJS += builtin/hook.o
 BUILTIN_OBJS += builtin/index-pack.o
 BUILTIN_OBJS += builtin/init-db.o

builtin.h

@@ -172,6 +172,7 @@ int cmd_get_tar_commit_id(int argc, const char **argv, const char *prefix, struc
 int cmd_grep(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_hash_object(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_help(int argc, const char **argv, const char *prefix, struct repository *repo);
+int cmd_history(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_hook(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_index_pack(int argc, const char **argv, const char *prefix, struct repository *repo);
 int cmd_init_db(int argc, const char **argv, const char *prefix, struct repository *repo);

builtin/history.c

@@ -0,0 +1,22 @@
+#include "builtin.h"
+#include "gettext.h"
+#include "parse-options.h"
+
+int cmd_history(int argc,
+		const char **argv,
+		const char *prefix,
+		struct repository *repo UNUSED)
+{
+	const char * const usage[] = {
+		N_("git history [<options>]"),
+		NULL,
+	};
+	struct option options[] = {
+		OPT_END(),
+	};
+
+	argc = parse_options(argc, argv, prefix, options, usage, 0);
+	if (argc)
+		usagef("unrecognized argument: %s", argv[0]);
+	return 0;
+}

command-list.txt

@@ -115,6 +115,7 @@ git-grep                                mainporcelain           info
 git-gui                                 mainporcelain
 git-hash-object                         plumbingmanipulators
 git-help                                ancillaryinterrogators          complete
+git-history                             mainporcelain           history
 git-hook                                purehelpers
 git-http-backend                        synchingrepositories
 git-http-fetch                          synchelpers

git.c

@@ -586,6 +586,7 @@ static struct cmd_struct commands[] = {
 	{ "grep", cmd_grep, RUN_SETUP_GENTLY },
 	{ "hash-object", cmd_hash_object },
 	{ "help", cmd_help },
+	{ "history", cmd_history, RUN_SETUP },
 	{ "hook", cmd_hook, RUN_SETUP },
 	{ "index-pack", cmd_index_pack, RUN_SETUP_GENTLY | NO_PARSEOPT },
 	{ "init", cmd_init_db },

meson.build

@@ -610,6 +610,7 @@ builtin_sources = [
   'builtin/grep.c',
   'builtin/hash-object.c',
   'builtin/help.c',
+  'builtin/history.c',
   'builtin/hook.c',
   'builtin/index-pack.c',
   'builtin/init-db.c',

t/meson.build

@@ -386,6 +386,7 @@ integration_tests = [
   't3436-rebase-more-options.sh',
   't3437-rebase-fixup-options.sh',
   't3438-rebase-broken-files.sh',
+  't3450-history.sh',
   't3500-cherry.sh',
   't3501-revert-cherry-pick.sh',
   't3502-cherry-pick-merge.sh',

t/t3450-history.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+test_description='tests for git-history command'
+
+. ./test-lib.sh
+
+test_expect_success 'does nothing without any arguments' '
+	git history >out 2>&1 &&
+	test_must_be_empty out
+'
+
+test_expect_success 'raises an error with unknown argument' '
+	test_must_fail git history garbage 2>err &&
+	test_grep "unrecognized argument: garbage" err
+'
+
+test_done