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

https://github.com/BurntSushi/ripgrep/blob/master/FAQ.md#complete

Author: scop

completions/Makefile.am

@@ -377,6 +377,7 @@ bashcomp_DATA = 2to3 \
 		_reptyr \
 		resolvconf \
 		_rfkill \
+		_rg \
 		ri \
 		rmlist \
 		rmmod \

completions/_rg

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

test/fallback/completions/rg

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