The submodule merge search is not useful during virtual merges because
the results cannot be used automatically.  Furthermore any suggestions
made by the search may apply to commits different than HEAD:sub and
MERGE_HEAD:sub, thus confusing the user.  Skip searching for submodule
merges during a virtual merge such as that between B and C while merging
the heads of:

    B---BC
   / \ /
  A   X
   \ / \
    C---CB

Run the search only when the recursion level is zero (!o->call_depth).
This fixes known breakage tested in t7405-submodule-merge.

Signed-off-by: Brad King <brad.king@kitware.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

* jk/argv-array:
  run_hook: use argv_array API
  checkout: use argv_array API
  bisect: use argv_array API
  quote: provide sq_dequote_to_argv_array
  refactor argv_array into generic code
  quote.h: fix bogus comment
  add sha1_array API docs

* jk/maint-fetch-submodule-check-fix:
  fetch: avoid quadratic loop checking for updated submodules

The submodule code recently grew generic code to build a
dynamic argv array. Many other parts of the code can reuse
this, too, so let's make it generically available.

There are two enhancements not found in the original code:

  1. We now handle the NULL-termination invariant properly,
     even when no strings have been pushed (before, you
     could have an empty, NULL argv). This was not a problem
     for the submodule code, which always pushed at least
     one argument, but was not sufficiently safe for
     generic code.

  2. There is a formatted variant of the "push" function.
     This is a convenience function which was not needed by
     the submodule code, but will make it easier to port
     other users to the new code.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Recent versions of git can be slow to fetch repositories with a
large number of refs (or when they already have a large
number of refs). For example, GitHub makes pull-requests
available as refs, which can lead to a large number of
available refs. This slowness goes away when submodule
recursion is turned off:

  $ git ls-remote git://github.com/rails/rails.git | wc -l
  3034

  [this takes ~10 seconds of CPU time to complete]
  git fetch --recurse-submodules=no \
    git://github.com/rails/rails.git "refs/*:refs/*"

  [this still isn't done after 10 _minutes_ of pegging the CPU]
  git fetch \
    git://github.com/rails/rails.git "refs/*:refs/*"

You can produce a quicker and simpler test case like this:

  doit() {
    head=`git rev-parse HEAD`
    for i in `seq 1 $1`; do
      echo $head refs/heads/ref$i
    done >.git/packed-refs
    echo "==> $1"
    rm -rf dest
    git init -q --bare dest &&
      (cd dest && time git.compile fetch -q .. refs/*:refs/*)
  }

  rm -rf repo
  git init -q repo && cd repo &&
  >file && git add file && git commit -q -m one

  doit 100
  doit 200
  doit 400
  doit 800
  doit 1600
  doit 3200

Which yields timings like:

  # refs  seconds of CPU
     100            0.06
     200            0.24
     400            0.95
     800            3.39
    1600           13.66
    3200           54.09

Notice that although the number of refs doubles in each
trial, the CPU time spent quadruples.

The problem is that the submodule recursion code works
something like:

  - for each ref we fetch
    - for each commit in git rev-list $new_sha1 --not --all
      - add modified submodules to list
  - fetch any newly referenced submodules

But that means if we fetch N refs, we start N revision
walks. Worse, because we use "--all", the number of refs we
must process that constitute "--all" keeps growing, too. And
you end up doing O(N^2) ref resolutions.

Instead, this patch structures the code like this:

  - for each sha1 we already have
    - add $old_sha1 to list $old
  - for each ref we fetch
    - add $new_sha1 to list $new
  - for each commit in git rev-list $new --not $old
    - add modified submodules to list
  - fetch any newly referenced submodules

This yields timings like:

  # refs  seconds of CPU
  100               0.00
  200               0.04
  400               0.04
  800               0.10
  1600              0.21
  3200              0.39

Note that the amount of effort doubles as the number of refs
doubles. Similarly, the fetch of rails.git takes about as
much time as it does with --recurse-submodules=no.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Signed-off-by: Junio C Hamano <gitster@pobox.com>

* jl/maint-fetch-submodule-check-fix:
  fetch: skip on-demand checking when no submodules are configured

It makes no sense to do the - possibly very expensive - call to "rev-list
<new-ref-sha1> --not --all" in check_for_new_submodule_commits() when
there aren't any submodules configured.

Leave check_for_new_submodule_commits() early when no name <-> path
mappings for submodules are found in the configuration. To make that work
reading the configuration had to be moved further up in cmd_fetch(), as
doing that after the actual fetch of the superproject was too late.

Reported-by: Martin Fick <mfick@codeaurora.org>
Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

* fg/submodule-ff-check-before-push:
  push: Don't push a repository with unpushed submodules

* nd/maint-clone-gitdir:
  clone: allow to clone from .git file
  read_gitfile_gently(): rename misnamed function to read_gitfile()