Some users do want to write a line that begin with a pound sign, #,
in their commit log message.  Many tracking system recognise
a token of #<bugid> form, for example.

The support we offer these use cases is not very friendly to the end
users.  They have a choice between

 - Don't do it.  Avoid such a line by rewrapping or indenting; and

 - Use --cleanup=whitespace but remove all the hint lines we add.

Give them a way to set a custom comment char, e.g.

    $ git -c core.commentchar="%" commit

so that they do not have to do either of the two workarounds.

[jc: although I started the topic, all the tests and documentation
updates, many of the call sites of the new strbuf_add_commented_*()
functions, and the change to git-submodule.sh scripted Porcelain are
from Ralf.]

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Ralf Thielow <ralf.thielow@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

This allows you to easily record a submodule.<name>.branch option in
.gitmodules when you add a new submodule.  With this patch,

  $ git submodule add -b <branch> <repository> [<path>]
  $ git config -f .gitmodules submodule.<path>.branch <branch>

reduces to

  $ git submodule add -b <branch> <repository> [<path>]

This means that future calls to

  $ git submodule update --remote ...

will get updates from the same branch that you used to initialize the
submodule, which is usually what you want.

Signed-off-by: W. Trevor King <wking@tremily.us>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

The current `update` command incorporates the superproject's gitlinked
SHA-1 ($sha1) into the submodule HEAD ($subsha1).  Depending on the
options you use, it may checkout $sha1, rebase the $subsha1 onto
$sha1, or merge $sha1 into $subsha1.  This helps you keep up with
changes in the upstream superproject.

However, it's also useful to stay up to date with changes in the
upstream subproject.  Previous workflows for incorporating such
changes include the ungainly:

  $ git submodule foreach 'git checkout $(git config --file $toplevel/.gitmodules submodule.$name.branch) && git pull'

With this patch, all of the useful functionality for incorporating
superproject changes can be reused to incorporate upstream subproject
updates.  When you specify --remote, the target $sha1 is replaced with
a $sha1 of the submodule's origin/master tracking branch.  If you want
to merge a different tracking branch, you can configure the
`submodule.<name>.branch` option in `.gitmodules`.  You can override
the `.gitmodules` configuration setting for a particular superproject
by configuring the option in that superproject's default configuration
(using the usual configuration hierarchy, e.g. `.git/config`,
`~/.gitconfig`, etc.).

Previous use of submodule.<name>.branch
=======================================

Because we're adding a new configuration option, it's a good idea to
check if anyone else is already using the option.  The foreach-pull
example above was described by Ævar in

  commit f030c96d8643fa0a1a9b2bd9c2f36a77721fb61f
  Author: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
  Date:   Fri May 21 16:10:10 2010 +0000

    git-submodule foreach: Add $toplevel variable

Gerrit uses the same interpretation for the setting, but because
Gerrit has direct access to the subproject repositories, it updates
the superproject repositories automatically when a subproject changes.
Gerrit also accepts the special value '.', which it expands into the
superproject's branch name.

Although the --remote functionality is using `submodule.<name>.branch`
slightly differently, the effect is the same.  The foreach-pull
example uses the option to record the name of the local branch to
checkout before pulls.  The tracking branch to be pulled is recorded
in `.git/modules/<name>/config`, which was initialized by the module
clone during `submodule add` or `submodule init`.  Because the branch
name stored in `submodule.<name>.branch` was likely the same as the
branch name used during the initial `submodule add`, the same branch
will be pulled in each workflow.

Implementation details
======================

In order to ensure a current tracking branch state, `update --remote`
fetches the submodule's remote repository before calculating the
SHA-1.  However, I didn't change the logic guarding the existing fetch:

  if test -z "$nofetch"
  then
    # Run fetch only if $sha1 isn't present or it
    # is not reachable from a ref.
    (clear_local_git_env; cd "$path" &&
      ( (rev=$(git rev-list -n 1 $sha1 --not --all 2>/dev/null) &&
       test -z "$rev") || git-fetch)) ||
    die "$(eval_gettext "Unable to fetch in submodule path '\$path'")"
  fi

There will not be a double-fetch, because the new $sha1 determined
after the `--remote` triggered fetch should always exist in the
repository.  If it doesn't, it's because some racy process removed it
from the submodule's repository and we *should* be re-fetching.

Signed-off-by: W. Trevor King <wking@tremily.us>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Several submodule configuration variables
(e.g. fetchRecurseSubmodules) are read from .gitmodules with local
overrides from the usual git config files.  This shell function mimics
that logic to help initialize configuration variables in
git-submodule.sh.

Signed-off-by: W. Trevor King <wking@tremily.us>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

* wtk/submodule-doc-fixup:
  git-submodule: wrap branch option with "<>" in usage strings.

Adds "--recursive" option to submodule sync.

* ph/submodule-sync-recursive:
  Add tests for submodule sync --recursive
  Teach --recursive to submodule sync

Cleans up some leftover bits from an earlier submodule change.

* ph/maint-submodule-status-fix:
  submodule status: remove unused orig_* variables
  t7407: Fix recursive submodule test

* sz/maint-submodule-reference-arg:
  submodule add: fix handling of --reference=<repo> option

If you remove a submodule, in order to keep the repository so that
"git checkout" to an older commit in the superproject history can
resurrect the submodule, the real repository will stay in $GIT_DIR
of the superproject.  A later "git submodule add $path" to add a
different submodule at the same path will fail.  Diagnose this case
a bit better, and if the user really wants to add an unrelated
submodule at the same path, give the "--name" option to give it a
place in $GIT_DIR of the superproject that does not conflict with
the original submodule.

* jl/submodule-add-by-name:
  submodule add: Fail when .git/modules/<name> already exists unless forced
  Teach "git submodule add" the --name option

The submodule sync command was somehow left out when
--recursive was added to the other submodule commands.

Teach sync to handle the --recursive switch by recursing
when we're in a submodule we are sync'ing.

Change the report during sync to show submodule-path
instead of submodule-name to be consistent with the other
submodule commands and to help recursed paths make sense.

Signed-off-by: Phil Hord <hordp@cisco.com>
Acked-By: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Jeff King <peff@peff.net>