feat(gh): add fallback 3rd party completion loader

Author: scop

completions/Makefile.am

@@ -130,6 +130,7 @@ bashcomp_DATA = 2to3 \
 		geoiplookup \
 		getconf \
 		getent \
+		_gh \
 		gkrellm \
 		gm \
 		gnatmake \

completions/_gh

@@ -0,0 +1,18 @@
+# 3rd party completion loader for commands emitting        -*- shell-script -*-
+# their completion using "$cmd completion --shell bash".
+#
+# This serves as a fallback in case the completion is not installed otherwise.
+
+# shellcheck disable=SC2168 # "local" is ok, assume sourced by __load_completion
+local _comp__load_3rdparty_reset_shopt=$(shopt -po posix)
+set +o posix
+
+. <("$1" completion --shell bash 2>/dev/null)
+
+$_comp__load_3rdparty_reset_shopt
+
+{
+    complete -p "$1" || complete -p "${1##*/}"
+} &>/dev/null
+
+# ex: filetype=sh

test/fallback/completions/Makefile.am

@@ -5,6 +5,7 @@ EXTRA_DIST = \
 	chsh \
 	dmesg \
 	eject \
+	gh \
 	hexdump \
 	hwclock \
 	ionice \

test/fallback/completions/gh

@@ -0,0 +1 @@
+../../../completions/_gh