[src/trunk]: src/usr.bin/make/unit-tests make: clarify what .export ${:U} means

[rillig <rillig%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/008ad9d73112
branches:  trunk
changeset: 959522:008ad9d73112
user:      rillig <rillig%NetBSD.org@localhost>
date:      Tue Feb 16 18:12:46 2021 +0000

description:
make: clarify what .export ${:U} means

diffstat:

 usr.bin/make/unit-tests/directive-export.mk |  7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diffs (22 lines):

diff -r c3196379e809 -r 008ad9d73112 usr.bin/make/unit-tests/directive-export.mk
--- a/usr.bin/make/unit-tests/directive-export.mk       Tue Feb 16 18:02:19 2021 +0000
+++ b/usr.bin/make/unit-tests/directive-export.mk       Tue Feb 16 18:12:46 2021 +0000
@@ -1,4 +1,4 @@
-# $NetBSD: directive-export.mk,v 1.6 2020/12/13 01:07:54 rillig Exp $
+# $NetBSD: directive-export.mk,v 1.7 2021/02/16 18:12:46 rillig Exp $
 #
 # Tests for the .export directive.
 #
@@ -28,8 +28,11 @@
 .  error
 .endif
 
-# No argument means to export all variables.
+# No syntactical argument means to export all variables.
 .export
 
+# An empty argument means no additional variables to export.
+.export ${:U}
+
 all:
        @:;