Autocomplete for git's plumbing commands

By default, git’s completion only shows “porcelain” commands such as add, commit, etc., and hides the low-level “plumbing” commands like read-tree.

$ git re<TAB>
rebase         remote         replace        reset          revert
reflog         repack         request-pull   restore

This behavior can be modified by setting the GIT_COMPLETION_SHOW_ALL_COMMANDS=1 environment variable so that plumbing commands are also shown, which is documented in its completion script.

GIT_COMPLETION_SHOW_ALL_COMMANDS

  When set to "1" suggest all commands, including plumbing commands
  which are hidden by default (e.g. "cat-file" on "git ca<TAB>").

$ export GIT_COMPLETION_SHOW_ALL_COMMANDS=1
$ git re<TAB>
read-tree      receive-pack   remote         remote-fd      replace        rerere         restore        rev-list
rebase         reflog         remote-ext     repack         request-pull   reset          revert         rev-parse