Merge branch 'ps/history'

"git history" history rewriting UI.

* ps/history:
  builtin/history: implement "reword" subcommand
  builtin: add new "history" command
  wt-status: provide function to expose status for trees
  replay: support updating detached HEAD
  replay: support empty commit ranges
  replay: small set of cleanups
  builtin/replay: move core logic into "libgit.a"
  builtin/replay: extract core logic to replay revisions

Author: gitster

.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 +1,73 @@
+git-history(1)
+==============
+
+NAME
+----
+git-history - EXPERIMENTAL: Rewrite history
+
+SYNOPSIS
+--------
+[synopsis]
+git history reword <commit> [--ref-action=(branches|head|print)]
+
+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. There are a couple of major differences though:
+
+* linkgit:git-history[1] can work in a bare repository as it does not need to
+  touch either the index or the worktree.
+* linkgit:git-history[1] does not execute any linkgit:githooks[5] at the
+  current point in time. This may change in the future.
+* linkgit:git-history[1] by default updates all branches that are descendants
+  of the original commit to point to the rewritten commit.
+
+Overall, linkgit:git-history[1] aims to provide a more opinionated way to modify
+your commit history that is simpler to use compared to linkgit:git-rebase[1] in
+general.
+
+Use linkgit:git-rebase[1] 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
+at once.
+
+LIMITATIONS
+-----------
+
+This command does not (yet) work with histories that contain merges. You
+should use linkgit:git-rebase[1] with the `--rebase-merges` flag instead.
+
+Furthermore, the command does not support operations that can result in merge
+conflicts. This limitation is by design as history rewrites are not intended to
+be stateful operations. The limitation can be lifted once (if) Git learns about
+first-class conflicts.
+
+COMMANDS
+--------
+
+The following commands are available to rewrite history in different ways:
+
+`reword <commit>`::
+	Rewrite the commit message of the specified commit. All the other
+	details of this commit remain unchanged. This command will spawn an
+	editor with the current message of that commit.
+
+OPTIONS
+-------
+
+`--ref-action=(branches|head|print)`::
+	Control which references will be updated by the command, if any. With
+	`branches`, all local branches that point to commits which are
+	descendants of the original commit will be rewritten. With `head`, only
+	the current `HEAD` reference will be rewritten. With `print`, all
+	updates as they would be performed with `branches` are printed in a
+	format that can be consumed by linkgit:git-update-ref[1].
+
+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

@@ -1285,6 +1285,7 @@ LIB_OBJS += repack-geometry.o
 LIB_OBJS += repack-midx.o
 LIB_OBJS += repack-promisor.o
 LIB_OBJS += replace-object.o
+LIB_OBJS += replay.o
 LIB_OBJS += repo-settings.o
 LIB_OBJS += repository.o
 LIB_OBJS += rerere.o
@@ -1417,6 +1418,7 @@ 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

@@ -196,6 +196,7 @@ 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);