[PATCH v4 0/4] Beginning of new merge strategy: New API, empty implementation

In this series, I show the new merge API I have developed in merge-ort, and show how it differs from that provided by merge-recursive. I do this in four steps, each corresponding to a patch.

Changes since v3:

 * Make 'fast-rebase' be a test-tool subcommand instead of a special hidden
   builtin, as suggested by Jonathan Tan and SZEDER Gábor

Elijah Newren (4):
  merge-ort: barebones API of new merge strategy with empty
    implementation
  merge-ort-wrappers: new convience wrappers to mimic the old merge API
  fast-rebase: demonstrate merge-ort's API via new test-tool command
  merge,rebase,revert: select ort or recursive by config or environment

 Makefile                    |   3 +
 builtin/merge.c             |  26 ++++-
 builtin/rebase.c            |   9 +-
 builtin/revert.c            |   2 +
 merge-ort-wrappers.c        |  62 +++++++++++
 merge-ort-wrappers.h        |  25 +++++
 merge-ort.c                 |  52 +++++++++
 merge-ort.h                 |  58 ++++++++++
 sequencer.c                 |  71 ++++++++++--
 t/helper/test-fast-rebase.c | 211 ++++++++++++++++++++++++++++++++++++
 t/helper/test-tool.c        |   1 +
 t/helper/test-tool.h        |   1 +
 12 files changed, 506 insertions(+), 15 deletions(-)
 create mode 100644 merge-ort-wrappers.c
 create mode 100644 merge-ort-wrappers.h
 create mode 100644 merge-ort.c
 create mode 100644 merge-ort.h
 create mode 100644 t/helper/test-fast-rebase.c

base-commit: 69986e19ffcfb9af674ae5180689ab7bbf92ed28
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-895%2Fnewren%2Fort-api-with-empty-implementation-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-895/newren/ort-api-with-empty-implementation-v4
Pull-Request: https://github.com/git/git/pull/895

Range-diff vs v3:

 1:  3357ea415e = 1:  3357ea415e merge-ort: barebones API of new merge strategy with empty implementation
 2:  d7f6a834ab = 2:  d7f6a834ab merge-ort-wrappers: new convience wrappers to mimic the old merge API
 3:  27ad756600 ! 3:  fce0db8778 fast-rebase: demonstrate merge-ort's API via temporary/hidden command
     @@ Metadata
      Author: Elijah Newren <newren@gmail.com>
      
       ## Commit message ##
     -    fast-rebase: demonstrate merge-ort's API via temporary/hidden command
     +    fast-rebase: demonstrate merge-ort's API via new test-tool command
      
     -    Add a special built-in that is only of use to git-developers and only
     -    during the development of merge-ort, and which is designed to
     -    immediately fail and print:
     -       git: 'fast-rebase' is not a git command
     -    unless a special GIT_TEST_MERGE_ALGORITHM environment variable is set.
     -
     -    This special builtin serves two purposes:
     +    Add a new test-tool command named 'fast-rebase', which is a
     +    super-slimmed down and nowhere near as capable version of 'git rebase'.
     +    'test-tool fast-rebase' is not currently planned for usage in the
     +    testsuite, but is here for two purposes:
      
            1) Demonstrate the desired API of merge-ort.  In particular,
               fast-rebase takes advantage of the separation of the merging
               operation from the updating of the index and working tree, to
               allow it to pick N commits, but only update the index and working
               tree once at the end.  Look for the calls to
     -         merge_inmemory_nonrecursive() and merge_switch_to_result().
     +         merge_incore_nonrecursive() and merge_switch_to_result().
      
            2) Provide a convenient benchmark that isn't polluted by the heavy
               disk writing and forking of unnecessary processes that comes from
     @@ Commit message
          Signed-off-by: Elijah Newren <newren@gmail.com>
      
       ## Makefile ##
     -@@ Makefile: BUILTIN_OBJS += builtin/difftool.o
     - BUILTIN_OBJS += builtin/env--helper.o
     - BUILTIN_OBJS += builtin/fast-export.o
     - BUILTIN_OBJS += builtin/fast-import.o
     -+BUILTIN_OBJS += builtin/fast-rebase.o
     - BUILTIN_OBJS += builtin/fetch-pack.o
     - BUILTIN_OBJS += builtin/fetch.o
     - BUILTIN_OBJS += builtin/fmt-merge-msg.o
     -
     - ## builtin.h ##
     -@@ builtin.h: int cmd_difftool(int argc, const char **argv, const char *prefix);
     - int cmd_env__helper(int argc, const char **argv, const char *prefix);
     - int cmd_fast_export(int argc, const char **argv, const char *prefix);
     - int cmd_fast_import(int argc, const char **argv, const char *prefix);
     -+int cmd_fast_rebase(int argc, const char **argv, const char *prefix);
     - int cmd_fetch(int argc, const char **argv, const char *prefix);
     - int cmd_fetch_pack(int argc, const char **argv, const char *prefix);
     - int cmd_fmt_merge_msg(int argc, const char **argv, const char *prefix);
     +@@ Makefile: TEST_BUILTINS_OBJS += test-dump-fsmonitor.o
     + TEST_BUILTINS_OBJS += test-dump-split-index.o
     + TEST_BUILTINS_OBJS += test-dump-untracked-cache.o
     + TEST_BUILTINS_OBJS += test-example-decorate.o
     ++TEST_BUILTINS_OBJS += test-fast-rebase.o
     + TEST_BUILTINS_OBJS += test-genrandom.o
     + TEST_BUILTINS_OBJS += test-genzeros.o
     + TEST_BUILTINS_OBJS += test-hash-speed.o
      
     - ## builtin/fast-rebase.c (new) ##
     + ## t/helper/test-fast-rebase.c (new) ##
      @@
      +/*
      + * "git fast-rebase" builtin command
     @@ builtin/fast-rebase.c (new)
      + */
      +
      +#define USE_THE_INDEX_COMPATIBILITY_MACROS
     -+#include "builtin.h"
     ++#include "test-tool.h"
      +
      +#include "cache-tree.h"
      +#include "commit.h"
     @@ builtin/fast-rebase.c (new)
      +	return (struct commit *)obj;
      +}
      +
     -+int cmd_fast_rebase(int argc, const char **argv, const char *prefix)
     ++int cmd__fast_rebase(int argc, const char **argv)
      +{
      +	struct commit *onto;
      +	struct commit *last_commit = NULL, *last_picked_commit = NULL;
     @@ builtin/fast-rebase.c (new)
      +	struct strbuf reflog_msg = STRBUF_INIT;
      +	struct strbuf branch_name = STRBUF_INIT;
      +
     ++	/*
     ++	 * test-tool stuff doesn't set up the git directory by default; need to
     ++	 * do that manually.
     ++	 */
     ++	setup_git_directory();
     ++
      +	if (argc == 2 && !strcmp(argv[1], "-h")) {
      +		printf("Sorry, I am not a psychiatrist; I can not give you the help you need.  Oh, you meant usage...\n");
      +		exit(129);
      +	}
      +
     -+	if (!getenv("GIT_TEST_MERGE_ALGORITHM")) {
     -+		fprintf_ln(stderr, _("git: 'fast-rebase' is not a git command. See 'git --help'."));
     -+		exit(1);
     -+	}
     -+
      +	if (argc != 5 || strcmp(argv[1], "--onto"))
      +		die("usage: read the code, figure out how to use it, then do so");
      +
     @@ builtin/fast-rebase.c (new)
      +	return (clean == 0);
      +}
      
     - ## git.c ##
     -@@ git.c: static struct cmd_struct commands[] = {
     - 	{ "env--helper", cmd_env__helper },
     - 	{ "fast-export", cmd_fast_export, RUN_SETUP },
     - 	{ "fast-import", cmd_fast_import, RUN_SETUP | NO_PARSEOPT },
     -+	{ "fast-rebase", cmd_fast_rebase, RUN_SETUP /* | NEED_WORK_TREE */ },
     - 	{ "fetch", cmd_fetch, RUN_SETUP },
     - 	{ "fetch-pack", cmd_fetch_pack, RUN_SETUP | NO_PARSEOPT },
     - 	{ "fmt-merge-msg", cmd_fmt_merge_msg, RUN_SETUP },
     + ## t/helper/test-tool.c ##
     +@@ t/helper/test-tool.c: static struct test_cmd cmds[] = {
     + 	{ "dump-split-index", cmd__dump_split_index },
     + 	{ "dump-untracked-cache", cmd__dump_untracked_cache },
     + 	{ "example-decorate", cmd__example_decorate },
     ++	{ "fast-rebase", cmd__fast_rebase },
     + 	{ "genrandom", cmd__genrandom },
     + 	{ "genzeros", cmd__genzeros },
     + 	{ "hashmap", cmd__hashmap },
     +
     + ## t/helper/test-tool.h ##
     +@@ t/helper/test-tool.h: int cmd__dump_fsmonitor(int argc, const char **argv);
     + int cmd__dump_split_index(int argc, const char **argv);
     + int cmd__dump_untracked_cache(int argc, const char **argv);
     + int cmd__example_decorate(int argc, const char **argv);
     ++int cmd__fast_rebase(int argc, const char **argv);
     + int cmd__genrandom(int argc, const char **argv);
     + int cmd__genzeros(int argc, const char **argv);
     + int cmd__hashmap(int argc, const char **argv);
 4:  0479d59c33 = 4:  75d19804bd merge,rebase,revert: select ort or recursive by config or environment