Add --keyring-backend argument completion for bash

keyring/backend_complete.bash

@@ -0,0 +1,14 @@
+# Complete keyring backends for `keyring -b` from `keyring --list-backends`
+# # keyring -b <TAB>
+# keyring.backends.chainer.ChainerBackend keyring.backends.fail.Keyring ...
+
+_keyring_backends() {
+	local choices
+	choices=$(
+		"${COMP_WORDS[0]}" --list-backends 2>/dev/null |
+			while IFS=$' \t' read -r backend rest; do
+				printf "%s\n" "$backend"
+			done
+	)
+	compgen -W "${choices[*]}" -- "$1"
+}

keyring/completion.py

@@ -36,11 +36,15 @@ def get_action(parser, option):
 
 def install_completion(parser):
     preamble = dict(
+        bash=files(__package__).joinpath('backend_complete.bash').read_text(),
         zsh=files(__package__).joinpath('backend_complete.zsh').read_text(),
     )
     shtab.add_argument_to(parser, preamble=preamble)
     get_action(parser, '--keyring-path').complete = shtab.DIR
-    get_action(parser, '--keyring-backend').complete = dict(zsh='backend_complete')
+    get_action(parser, '--keyring-backend').complete = dict(
+        bash='_keyring_backends',
+        zsh='backend_complete',
+    )
     return parser