Add bash completion

Closes https://github.com/sharkdp/bat/issues/1010

assets/completions/bat.bash.in

@@ -0,0 +1,84 @@
+# shellcheck disable=SC2207
+
+_bat() {
+	if [[ ${COMP_WORDS[1]-} == cache ]]; then
+		case $3 in
+		--source | --target)
+			local IFS=$'\n'
+			COMPREPLY=($(compgen -d -- "$2"))
+			compopt -o filenames
+			return 0
+			;;
+		esac
+		COMPREPLY=($(compgen -W "
+			--build --clear --source --target --blank --help
+		" -- "$2"))
+		return 0
+	fi
+
+	case $3 in
+	-l | --language)
+		local IFS=$'\n'
+		COMPREPLY=($(compgen -W "$(
+			"$1" --list-languages | while IFS=: read -r lang _; do
+				printf "%s\n" "$lang"
+			done
+		)" -- "$2"))
+		compopt -o filenames  # for escaping
+		return 0
+		;;
+	-H | --highlight-line | --diff-context | --tabs | --terminal-width | \
+	-m | --map-syntax | --style | --line-range | -h | --help | -V | \
+	--version)
+		# argument required but no completion available, or argument
+		# causes an exit
+		return 0
+		;;
+	--file-name)
+		local IFS=$'\n'
+		COMPREPLY=($(compgen -f -- "$2"))
+		compopt -o filenames
+		return 0
+		;;
+	--wrap)
+		COMPREPLY=($(compgen -W "auto never character" -- "$2"))
+		return 0
+		;;
+	--color | --decorations | --paging)
+		COMPREPLY=($(compgen -W "auto never always" -- "$2"))
+		return 0
+		;;
+	--italic-text)
+		COMPREPLY=($(compgen -W "always never" -- "$2"))
+		return 0
+		;;
+	--pager)
+		COMPREPLY=($(compgen -c -- "$2"))
+		return 0
+		;;
+	--theme)
+		local IFS=$'\n'
+		COMPREPLY=($(compgen -W "$("$1" --list-themes)" -- "$2"))
+		compopt -o filenames
+		return 0
+		;;
+	esac
+
+	if [[ $2 == -* ]]; then
+		COMPREPLY=($(compgen -W "
+			--show-all --plain --language --highlight-line
+			--file-name --diff --diff-context --tabs --wrap
+			--terminal-width --number --color --italic-text
+			--decorations --paging --pager --map-syntax --theme
+			--list-themes --style --line-range --list-languages
+			--help --version
+		" -- "$2"))
+		return 0
+	fi
+
+	local IFS=$'\n'
+	COMPREPLY=($(compgen -f -- "$2"))
+	compopt -o filenames
+	((COMP_CWORD == 1)) && COMPREPLY+=($(compgen -W cache -- "$2"))
+
+} && complete -F _bat {{PROJECT_EXECUTABLE}}