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author | Eric Blake <eblake@redhat.com> | 2016-12-22 13:03:21 -0600 |
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committer | Eric Blake <eblake@redhat.com> | 2016-12-22 13:34:35 -0600 |
commit | a6b2acf29d66a1824572c27c2104d24a2b034790 (patch) | |
tree | 5a4a58c59c90f939b33ddf0f5ffbeba26a47bece /doc/autoconf.texi | |
parent | 78ad1b0b2cea606bf401ed0262540b503db73e1c (diff) | |
download | autoconf-a6b2acf29d66a1824572c27c2104d24a2b034790.tar.gz |
doc: Patterns in m4_pattern_forbid cause error, not warning
The example text regarding a desired literal AC_DC in output
claimed that the result would trigger a warning if one does
not use creative quoting; but in reality, autoconf's use of
m4_pattern_forbid to reserve the entire AC_ namespace makes
it a hard error. Reword the section to mention the use of
m4_pattern_allow() as the fix, and beef up the example to
better demonstrate the problem.
* doc/autoconf.texi (Autoconf Language): Improve AC_DC example.
Reported by Gavin Smith <gavinsmith0123@gmail.com>.
Signed-off-by: Eric Blake <eblake@redhat.com>
Diffstat (limited to 'doc/autoconf.texi')
-rw-r--r-- | doc/autoconf.texi | 33 |
1 files changed, 21 insertions, 12 deletions
diff --git a/doc/autoconf.texi b/doc/autoconf.texi index 7e710a57..01a83136 100644 --- a/doc/autoconf.texi +++ b/doc/autoconf.texi @@ -1243,13 +1243,21 @@ AC_CHECK_HEADER(stdio.h, AC_MSG_ERROR([sorry, can't do anything for you])) @end example -In other cases, you may have to use text that also resembles a macro -call. You must quote that text even when it is not passed as a macro -argument. For example, these two approaches in @file{configure.ac} -(quoting just the potential problems, or quoting the entire line) will -protect your script in case autoconf ever adds a macro @code{AC_DC}: - -@example +In other cases, you may want to use text that also resembles a macro +call. You must quote that text (whether just the potential problem, or +the entire line) even when it is not passed as a macro argument; and you +may also have to use @code{m4_pattern_allow} (@pxref{Forbidden +Patterns}), to declare your intention that the resulting configure file +will have a literal that resembles what would otherwise be reserved for +a macro name. For example: + +@example +dnl Simulate a possible future autoconf macro +m4_define([AC_DC], [oops]) +dnl Underquoted: +echo "Hard rock was here! --AC_DC" +dnl Correctly quoted: +m4_pattern_allow([AC_DC]) echo "Hard rock was here! --[AC_DC]" [echo "Hard rock was here! --AC_DC"] @end example @@ -1258,6 +1266,7 @@ echo "Hard rock was here! --[AC_DC]" which results in this text in @file{configure}: @example +echo "Hard rock was here! --oops" echo "Hard rock was here! --AC_DC" echo "Hard rock was here! --AC_DC" @end example @@ -1270,15 +1279,15 @@ quoting for all literal string arguments}, either around just the problematic portions, or over the entire argument: @example +m4_pattern_allow([AC_DC]) AC_MSG_WARN([[AC_DC] stinks --Iron Maiden]) AC_MSG_WARN([[AC_DC stinks --Iron Maiden]]) @end example -However, the above example triggers a warning about a possibly -unexpanded macro when running @command{autoconf}, because it collides -with the namespace of macros reserved for the Autoconf language. To be -really safe, you can use additional escaping (either a quadrigraph, or -creative shell constructs) to silence that particular warning: +It is also possible to avoid the problematic patterns in the first +place, by the use of additional escaping (either a quadrigraph, or +creative shell constructs), in which case it is no longer necessary to +use @code{m4_pattern_allow}: @example echo "Hard rock was here! --AC""_DC" |