Since 0cfd1120 (am: preliminary support for hg patches, 2011-08-29),
git-am.sh could convert mercurial patches to an RFC2822 mail patch
suitable for parsing with git-mailinfo, and queue them in the state
directory for application.

Since 15ced753 (git-am foreign patch support: autodetect some patch
formats, 2009-05-27), git-am.sh was able to auto-detect mercurial
patches by checking if the file begins with the line:

	# HG changeset patch

Re-implement the above in builtin/am.c.
Helped-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since c574e683 (git-am foreign patch support: StGIT support, 2009-05-27),
git-am.sh is able to read a single StGit series file and, for each StGit
patch listed in the file, convert the StGit patch into a RFC2822 mail
patch suitable for parsing with git-mailinfo, and queue them in the
state directory for applying.

Since 15ced753 (git-am foreign patch support: autodetect some patch
formats, 2009-05-27), git-am.sh is able to auto-detect StGit series
files by checking to see if the file starts with the string:

	# This series applies on GIT commit

Re-implement the above in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since c574e683 (git-am foreign patch support: StGIT support, 2009-05-27),
git-am.sh supported converting StGit patches into RFC2822 mail patches
that can be parsed with git-mailinfo.

Implement this by introducing two functions in builtin/am.c:
stgit_patch_to_mail() and split_mail_conv().

stgit_patch_to_mail() is a callback function for split_mail_conv(), and
contains the logic for converting an StGit patch into an RFC2822 mail
patch.

split_mail_conv() implements the logic to go through each file in the
`paths` list, reading from stdin where specified, and calls the callback
function to write the converted patch to the corresponding output file
in the state directory. This interface should be generic enough to
support other foreign patch formats in the future.

Since 15ced753 (git-am foreign patch support: autodetect some patch
formats, 2009-05-27), git-am.sh is able to auto-detect StGit patches.
Re-implement this in builtin/am.c.
Helped-by: NEric Sunshine <sunshine@sunshineco.com>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-am.sh will call git-rerere at the following events:

* "git rerere" when a three-way merge fails to record the conflicted
  automerge results. Since 8389b52b (git-rerere: reuse recorded resolve.,
  2006-01-28)

  * Since cb6020bb (Teach --[no-]rerere-autoupdate option to merge,
    revert and friends, 2009-12-04), git-am.sh supports the
    --[no-]rerere-autoupdate option as well, and would pass it to
    git-rerere.

* "git rerere" when --resolved, to record the hand resolution. Since
  f131dd49 (rerere: record (or avoid misrecording) resolved, skipped or
  aborted rebase/am, 2006-12-08)

* "git rerere clear" when --skip-ing. Since f131dd49 (rerere: record (or
  avoid misrecording) resolved, skipped or aborted rebase/am,
  2006-12-08)

* "git rerere clear" when --abort-ing. Since 3e5057a8 (git am --abort,
  2008-07-16)

Re-implement the above in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07),
git-am.sh will invoke the post-applypatch hook after the patch is
applied and a commit is made. The exit code of the hook is ignored.

Re-implement this in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07),
git-am.sg will invoke the pre-applypatch hook after applying the patch
to the index, but before a commit is made. Should the hook exit with a
non-zero status, git am will exit.

Re-implement this in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07),
git-am.sh will invoke the applypatch-msg hooks just after extracting the
patch message. If the applypatch-msg hook exits with a non-zero status,
git-am.sh abort before even applying the patch to the index.

Re-implement this in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since eb2151bb (rebase: support automatic notes copying, 2010-03-12),
git-am.sh supported automatic notes copying in --rebasing mode by
invoking "git notes copy" once it has finished applying all the patches.

Re-implement this feature in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 96e19488 (rebase: invoke post-rewrite hook, 2010-03-12), git-am.sh
will invoke the post-rewrite hook after it successfully finishes
applying all the queued patches.

To do this, when parsing a mail to extract its patch and metadata, in
--rebasing mode git-am.sh will also store the original commit ID in the
$state_dir/original-commit file. Once it applies and commits the patch,
the original commit ID, and the new commit ID, will be appended to the
$state_dir/rewritten file.

Once all of the queued mail have been processed, git-am.sh will then
invoke the post-rewrite hook with the contents of the
$state_dir/rewritten file.

Re-implement this in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 3b4e395f (am: add the --gpg-sign option, 2014-02-01), git-am.sh
supported the --gpg-sign option, and would pass it to git-commit-tree,
thus GPG-signing the commit object.

Re-implement this option in builtin/am.c.

git-commit-tree would also sign the commit by default if the
commit.gpgsign setting is true. Since we do not run commit-tree, we
re-implement this behavior by handling the commit.gpgsign setting
ourselves.
Helped-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 3f01ad66 (am: Add --committer-date-is-author-date option,
2009-01-22), git-am.sh implemented the --committer-date-is-author-date
option, which tells git-am to use the timestamp recorded in the email
message as both author and committer date.

Re-implement this option in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since a79ec62d (git-am: Add --ignore-date option, 2009-01-24), git-am.sh
supported the --ignore-date option, and would use the current timestamp
instead of the one provided in the patch if the option was set.

Re-implement this option in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-am.sh recognizes some of git-apply's options, and would pass them to
git-apply:

* --whitespace, since 8c31cb82 (git-am: --whitespace=x option.,
  2006-02-28)

* -C, since 67dad687 (add -C[NUM] to git-am, 2007-02-08)

* -p, since 2092a1fe (Teach git-am to pass -p option down to git-apply,
  2007-02-11)

* --directory, since b47dfe9e (git-am: add --directory=<dir> option,
  2009-01-11)

* --reject, since b80da424 (git-am: implement --reject option passed to
  git-apply, 2009-01-23)

* --ignore-space-change, --ignore-whitespace, since 86c91f91 (git apply:
  option to ignore whitespace differences, 2009-08-04)

* --exclude, since 77e9e496 (am: pass exclude down to apply, 2011-08-03)

* --include, since 58725efd (am: support --include option, 2012-03-28)

* --reject, since b80da424 (git-am: implement --reject option passed to
  git-apply, 2009-01-23)

Re-implement support for these options in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 017678b4 (am/mailinfo: Disable scissors processing by default,
2009-08-26), git-am supported the --[no-]scissors option, passing it to
git-mailinfo.

Re-implement support for this option in builtin/am.c.

Since the default setting of --scissors in git-mailinfo can be
configured with mailinfo.scissors (and perhaps through other settings in
the future), to be safe we make an explicit distinction between
SCISSORS_UNSET, SCISSORS_TRUE and SCISSORS_FALSE.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since ad2c9280 (git-am: Add command line parameter `--keep-cr` passing it
to git-mailsplit, 2010-02-27), git-am.sh supported the --keep-cr option
and would pass it to git-mailsplit.

Since e80d4cbe (git-am: Add am.keepcr and --no-keep-cr to override it,
2010-02-27), git-am.sh supported the am.keepcr config setting, which
controls whether --keep-cr is on by default.

Re-implement the above in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since a078f732 (git-am: add --message-id/--no-message-id, 2014-11-25),
git-am.sh supported the --[no-]message-id options, and the
"am.messageid" setting which specifies the default option.

--[no-]message-id tells git-am whether or not the -m option should be
passed to git-mailinfo.

Re-implement this option in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07),
git-am.sh supported the -k/--keep option to pass the -k option to
git-mailsplit.

Since f7e5ea17 (am: learn passing -b to mailinfo, 2012-01-16), git-am.sh
supported the --keep-non-patch option to pass the -b option to
git-mailsplit.

Re-implement these two options in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07),
git-am.sh supported the -u,--utf8 option. If set, the -u option will be
passed to git-mailinfo to re-code the commit log message and authorship
in the charset specified by i18n.commitencoding. If unset, the -n option
will be passed to git-mailinfo, which disables the re-encoding.

Since d84029b6 (--utf8 is now default for 'git-am', 2007-01-08), --utf8
is specified by default in git-am.sh.

Re-implement the above in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Should git-am terminate unexpectedly between the point where the state
directory is created, but the "next" and "last" files are not written
yet, a stray state directory will be left behind.

As such, since b141f3c9 (am: handle stray $dotest directory, 2013-06-15),
git-am.sh explicitly recognizes such a stray directory, and allows the
user to remove it with am --abort.

Re-implement this feature in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 5e835cac (rebase: do not munge commit log message, 2008-04-16),
git am --rebasing no longer gets the commit log message from the patch,
but reads it directly from the commit identified by the "From " header
line.

Since 43c23251 (am: use get_author_ident_from_commit instead of mailinfo
when rebasing, 2010-06-16), git am --rebasing also gets the author name,
email and date directly from the commit.

Since 0fbb95dc (am: don't call mailinfo if $rebasing, 2012-06-26), git am
--rebasing does not use git-mailinfo to get the patch body, but rather
generates it directly from the commit itself.

The above 3 commits introduced a separate parse_mail() code path in
git-am.sh's --rebasing mode that bypasses git-mailinfo. Re-implement
this code path in builtin/am.c as parse_mail_rebase().
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 3041c324 (am: --rebasing, 2008-03-04), git-am.sh supported the
--rebasing option, which is used internally by git-rebase to tell git-am
that it is being used for its purpose. It would create the empty file
$state_dir/rebasing to help "completion" scripts tell if the ongoing
operation is am or rebase.

As of 0fbb95dc (am: don't call mailinfo if $rebasing, 2012-06-26),
--rebasing also implies --3way as well.

Since a1549e10 (am: return control to caller, for housekeeping,
2013-05-12), git-am.sh would only clean up the state directory when it
is not --rebasing, instead deferring cleanup to git-rebase.sh.

Re-implement the above in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07),
git-am.sh supported the --3way option, and if set, would attempt to do a
3-way merge if the initial patch application fails.

Since 5d86861c (am -3: list the paths that needed 3-way fallback,
2012-03-28), in a 3-way merge git-am.sh would list the paths that needed
3-way fallback, so that the user can review them more carefully to spot
mismerges.

Re-implement the above in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07), git-am
supported the --signoff option which will append a signoff at the end of
the commit messsage. Re-implement this feature in parse_mail() by
calling append_signoff() if the option is set.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since ced9456a (Give the user a hint for how to continue in the case that
git-am fails because it requires user intervention, 2006-05-02), git-am
prints additional information on how the user can re-invoke git-am to
resume patch application after resolving the failure. Re-implement this
through the die_user_resolve() function.

Since cc120056 (Make git rebase interactive help match documentation.,
2006-05-13), git-am supports the --resolvemsg option which is used by
git-rebase to override the message printed out when git-am fails.
Re-implement this option.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 0e987a12 (am, rebase: teach quiet option, 2009-06-16), git-am
supported the --quiet option, and when told to be quiet, would only
speak on failure. Re-implement this by introducing the say() function,
which works like fprintf_ln(), but would only write to the stream when
state->quiet is false.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07), git-am
would error out if the user gave it mbox(s) on the command-line, but
there was a session in progress.

Since c95b1389 (Fix git-am safety checks, 2006-09-15), git-am would
detect if the user attempted to feed it a mbox via stdin, by checking if
stdin is not a tty and there is no resume command given.

Re-implement the above two safety checks.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 3e5057a8 (git am --abort, 2008-07-16), git-am supported the --abort
option that will rewind HEAD back to the original commit. Re-implement
this through am_abort().

Since 7b3b7e37 (am --abort: keep unrelated commits since the last failure
and warn, 2010-12-21), to prevent commits made since the last failure
from being lost, git-am will not rewind HEAD back to the original
commit if HEAD moved since the last failure. Re-implement this through
safe_to_abort().
Helped-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07), git-am
supported resuming from a failed patch application by skipping the
current patch. Re-implement this feature by introducing am_skip().
Helped-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 271440e3 (git-am: make it easier after fixing up an unapplicable
patch., 2005-10-25), when "git am" is run again after being paused, the
current mail message will not be re-parsed, but instead the contents of
the state directory's patch, msg and author-script files will be used
as-is instead.

Re-implement this in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 0c15cc92 (git-am: --resolved., 2005-11-16), git-am supported
resuming from a failed patch application. The user will manually apply
the patch, and the run git am --resolved which will then commit the
resulting index. Re-implement this feature by introducing am_resolve().

Since it makes no sense for the user to run am --resolved when there is
no session in progress, we error out in this case.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since d1c5f2a4 (Add git-am, applymbox replacement., 2005-10-07), git-am
will refuse to apply patches if the index is dirty. Re-implement this
behavior in builtin/am.c.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Implement do_commit(), which commits the index which contains the
results of applying the patch, along with the extracted commit message
and authorship information.

Since 29b67543 (am: remove rebase-apply directory before gc, 2010-02-22),
git gc --auto is also invoked to pack the loose objects that are created
from making the commits.
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Implement applying the patch to the index using git-apply.

If a file is unchanged but stat-dirty, git-apply may erroneously fail to
apply patches, thinking that they conflict with a dirty working tree.

As such, since 2a6f08ac (am: refresh the index at start and --resolved,
2011-08-15), git-am will refresh the index before applying patches.
Re-implement this behavior.
Helped-by: NJunio C Hamano <gitster@pobox.com>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

For the purpose of applying the patch and committing the results,
implement extracting the patch data, commit message and authorship from
an e-mail message using git-mailinfo.

git-mailinfo is run as a separate process, but ideally in the future,
we should be be able to access its functionality directly without
spawning a new process.
Helped-by: NJunio C Hamano <gitster@pobox.com>
Helped-by: NJeff King <peff@peff.net>
Helped-by: NJohannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Since 15ced753 (git-am foreign patch support: autodetect some patch
formats, 2009-05-27), git-am.sh is able to autodetect mbox, stgit and
mercurial patches through heuristics.

Re-implement support for autodetecting mbox/maildir files in
builtin/am.c.

RFC 2822 requires that lines are terminated by "\r\n". To support this,
implement strbuf_getline_crlf(), which will remove both '\n' and "\r\n"
from the end of the line.
Helped-by: NJunio C Hamano <gitster@pobox.com>
Helped-by: NEric Sunshine <sunshine@sunshineco.com>
Helped-by: NJohannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-am.sh supports mbox, stgit and mercurial patches. Re-implement
support for splitting out mbox/maildirs using git-mailsplit, while also
implementing the framework required to support other patch formats in
the future.

Re-implement support for the --patch-format option (since a5a6755a
(git-am foreign patch support: introduce patch_format, 2009-05-27)) to
allow the user to choose between the different patch formats.
Helped-by: NJunio C Hamano <gitster@pobox.com>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-am applies a series of patches. If the process terminates
abnormally, we want to be able to resume applying the series of patches.
This requires the session state to be saved in a persistent location.

Implement the mechanism of a "patch queue", represented by 2 integers --
the index of the current patch we are applying and the index of the last
patch, as well as its lifecycle through the following functions:

* am_setup(), which will set up the state directory
  $GIT_DIR/rebase-apply. As such, even if the process exits abnormally,
  the last-known state will still persist.

* am_load(), which is called if there is an am session in
  progress, to load the last known state from the state directory so we
  can resume applying patches.

* am_run(), which will do the actual patch application. After applying a
  patch, it calls am_next() to increment the current patch index. The
  logic for applying and committing a patch is not implemented yet.

* am_destroy(), which is finally called when we successfully applied all
  the patches in the queue, to clean up by removing the state directory
  and its contents.
Helped-by: NJunio C Hamano <gitster@pobox.com>
Helped-by: NStefan Beller <sbeller@google.com>
Helped-by: NJohannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

For the purpose of rewriting git-am.sh into a C builtin, implement a
skeletal builtin/am.c that redirects to $GIT_EXEC_PATH/git-am if the
environment variable _GIT_USE_BUILTIN_AM is not defined. Since in the
Makefile git-am.sh takes precedence over builtin/am.c,
$GIT_EXEC_PATH/git-am will contain the shell script git-am.sh, and thus
this allows us to fall back on the functional git-am.sh when running the
test suite for tests that depend on a working git-am implementation.

Since git-am.sh cannot handle any environment modifications by
setup_git_directory(), "am" is declared with no setup flags in git.c. On
the other hand, to re-implement git-am.sh in builtin/am.c, we need to
run all the git dir and work tree setup logic that git.c typically does
for us. As such, we work around this temporarily by copying the logic in
git.c's run_builtin(), which is roughly:

	prefix = setup_git_directory();
	trace_repo_setup(prefix);
	setup_work_tree();

This redirection should be removed when all the features of git-am.sh
have been re-implemented in builtin/am.c.
Helped-by: NJunio C Hamano <gitster@pobox.com>
Signed-off-by: NPaul Tan <pyokagan@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>