Add bash completions for git-forgit (#235)

When using forgit as a subcommand of git, put 'git-forgit.bash' in one
of the following places and it will be loaded automatically on tab
completion of 'git forgit' or any configured git aliases of it:

- /usr/share/bash-completion/completions
- ~/.local/share/bash-completion/completions

README.md

@@ -289,6 +289,8 @@ export FORGIT_LOG_FZF_OPTS='
 - `gd` supports specifying revision(eg, `gd HEAD~`, `gd v1.0 README.md`).
 - Call `gi` with arguments to get the wanted `.gitignore` contents directly(eg, `gi cmake c++`).
 - You can use the commands as sub-commands of `git`, see [#147](https://github.com/wfxr/forgit/issues/147) for details.
+- Put [completions/git-forgit.bash](https://github.com/wfxr/forgit/blob/master/completions/git-forgit.bash) in
+  `~/.local/share/bash-completion/completions` to have bash tab completion for `git forgit` and configured git aliases.
 
 ### 📃 License
 

completions/git-forgit.bash

@@ -0,0 +1,106 @@
+# forgit completions for bash
+
+# When using forgit as a subcommand of git, put this file in one of the
+# following places and it will be loaded automatically on tab completion of
+# 'git forgit' or any configured git aliases of it:
+#
+#   /usr/share/bash-completion/completions
+#   ~/.local/share/bash-completion/completions
+
+_git_branch_delete()
+{
+	__gitcomp_nl "$(__git_heads)"
+}
+
+_git_checkout_branch()
+{
+	__gitcomp_nl "$(__git branch -a --format '%(refname:short)')"
+}
+
+_git_checkout_file()
+{
+	__gitcomp_nl "$(__git ls-files --modified)"
+}
+
+_git_checkout_tag()
+{
+	__gitcomp_nl "$(__git_tags)"
+}
+
+_git_stash_show()
+{
+	__gitcomp_nl "$(__git stash list | sed -n -e 's/:.*//p')"
+}
+
+# Completion for git-forgit
+# This includes git aliases, e.g. "alias.cb=forgit checkout_branch" will
+# correctly complete available branches on "git cb".
+_git_forgit()
+{
+	local subcommand cword cur prev cmds
+
+	subcommand="${COMP_WORDS[1]}"
+	if [[ "$subcommand" != "forgit" ]]
+	then
+		# Forgit is obviously called via a git alias. Get the original
+		# aliased subcommand and proceed as if it was the previous word.
+		prev=$(git config --get "alias.$subcommand" | cut -d' ' -f 2)
+		cword=$((${COMP_CWORD} + 1))
+	else
+		cword=${COMP_CWORD}
+		prev=${COMP_WORDS[COMP_CWORD-1]}
+	fi
+
+	cur=${COMP_WORDS[COMP_CWORD]}
+
+	cmds="
+		add
+		blame
+		branch_delete
+		checkout_branch
+		checkout_commit
+		checkout_file
+		checkout_tag
+		cherry_pick
+		cherry_pick_from_branch
+		clean
+		diff
+		fixup
+		ignore
+		log
+		rebase
+		reset_head
+		revert_commit
+		stash_show
+		stash_push
+	"
+
+	case ${cword} in
+		2)
+			COMPREPLY=($(compgen -W "${cmds}" -- ${cur}))
+			;;
+		3)
+			case ${prev} in
+				add) _git_add ;;
+				branch_delete) _git_branch_delete ;;
+				checkout_branch) _git_checkout_branch ;;
+				checkout_commit) _git_checkout ;;
+				checkout_file) _git_checkout_file ;;
+				checkout_tag) _git_checkout_tag ;;
+				cherry_pick) _git_cherry_pick ;;
+				cherry_pick_from_branch) _git_checkout_branch ;;
+				clean) _git_clean ;;
+				diff) _git_diff ;;
+				fixup) _git_branch ;;
+				log) _git_log ;;
+				rebase) _git_rebase ;;
+				reset_head) _git_reset ;;
+				revert_commit) _git_revert ;;
+				stash_show) _git_stash_show ;;
+			esac
+			;;
+		*)
+			COMPREPLY=()
+			;;
+	esac
+}