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

https://github.com/sigoden/argc

Author: scop

completions/Makefile.am

@@ -16,6 +16,7 @@ cross_platform = 2to3 \
 		apt-mark \
 		aptitude \
 		arch \
+		_argc \
 		arp \
 		arping \
 		arpspoof \

completions/_argc

@@ -0,0 +1,8 @@
+# 3rd party completion loader for commands emitting        -*- shell-script -*-
+# their completion using "$cmd --argc-completions bash".
+#
+# This serves as a fallback in case the completion is not installed otherwise.
+
+eval -- "$("$1" --argc-completions bash 2>/dev/null)"
+
+# ex: filetype=sh

test/fallback/completions/Makefile.am

@@ -1,4 +1,5 @@
 EXTRA_DIST = \
+	argc \
 	adb \
 	cal \
 	cargo \

test/fallback/completions/argc

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