Moving (renaming) submodules, recipe/script

["W. Trevor King" <wking@tremily.us>]

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Today I had to move my first submodule, and I discovered that Git's
support for this is pretty limited.  There have been a few patch
series attempting to address this [1,2], but none of them seems to
have pushed through into master (although I can't put my finger on a
reason for why).  There are also some SO postings discussing this
[3,4].  It would be nice if `git mv` worked out of the box on
submodules.  Failing that, there could be a `git submodule mv` command
that casts the appropriate spell.  Failing that, there could be a
recipe in Documentation/git-submodule.txt.  Here's the best I could
come up with for a `git-submodule-mv.sh`:

  #!/bin/sh
  # usage: git-submodule-mv.sh OLD NEW
  OLD=$(realpath --relative-to . "$1")
  NEW=$(realpath --relative-to . "$2")
  SHA=$(git ls-files -s "$OLD" | sed 's|^[0-9]* \([0-9a-f]*\) .*|\1|')
  NAME=$(git config -f .gitmodules --get-regexp 'submodule\..*\.path' "$OLD" |
    sed -e 's|^submodule.||' -e "s|.path $OLD\$||")
  GITDIR=$(realpath --relative-to "$NEW" .git/modules/"$NAME")
  git config -f .gitmodules submodule."$NAME".path "$NEW"
  git config -f .git/modules/"$NAME"/config core.worktree "../../../$NEW"
  git rm --cached "$OLD"
  mv "$OLD" "$NEW"
  echo "gitdir: $GITDIR" > "$NEW/.git"
  git update-index --add --cacheinfo 160000 "$SHA" "$NEW"

This only works from the repository root directory, and I'm sure makes
a number of poor assumptions (e.g. old-style submodules that don't use
`gitdir` links are not supported).  It does work for some simple test
cases.  The tricky parts (e.g. path -> name conversion) are already
worked out more robustly git-submodule.sh, so adding a new cmd_mv
shouldn't be very difficult.

Could something like this live somewhere in Git, or are we waiting for
a more integrated solution?

Cheers,
Trevor

[1]: http://thread.gmane.org/gmane.comp.version-control.git/88720
[2]: http://thread.gmane.org/gmane.comp.version-control.git/143250
[4]: http://stackoverflow.com/questions/4323558/moving-submodules-with-git
[3]: http://stackoverflow.com/questions/4604486/how-do-i-move-an-existing-git-submodule-within-a-git-repository

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