Re: autoconf-2.68: no AC_LANG_SOURCE call detected in body

[Eric Blake]

On 06/14/2011 01:02 AM, Křištof Želechovski wrote:
> Please observe that the following code from 3.1.2 "The Autoconf Language" is 
> obsolete and should be updated:

Not so much obsolete, but out of date with best practice.  At any rate,
thanks for the report!

> 
>       AC_COMPILE_IFELSE([[char b[10];]], [], [AC_MSG_ERROR([you lose])])
> 
> Running this snippet through autoconf produces the warning:
> 
>       no AC_LANG_SOURCE call detected in body
> 
> It seems the following syntax is required instead:
> 
>       AC_COMPILE_IFELSE([AC_LANG_SOURCE([[char b[10];]])], [], 
> [AC_MSG_ERROR([you lose])])

Indeed.  Here's what I'm pushing:

diff --git i/ChangeLog w/ChangeLog
index 1fca7bb..03541e0 100644
--- i/ChangeLog
+++ w/ChangeLog
@@ -1,3 +1,10 @@
+2011-06-14  Eric Blake  <address@hidden>
+
+       doc: update quoting example
+       * doc/autoconf.texi (Autoconf Language): Add AC_LANG_SOURCE use.
+       * THANKS: Update.
+       Reported by Křištof Želechovski.
+
 2011-05-05  Eric Blake  <address@hidden>

        doc: document dash bug with positional parameters
diff --git i/THANKS w/THANKS
index 7679b05..e125ebe 100644
--- i/THANKS
+++ w/THANKS
diff --git i/doc/autoconf.texi w/doc/autoconf.texi
index 7ff693f..99b1fd1 100644
--- i/doc/autoconf.texi
+++ w/doc/autoconf.texi
@@ -1288,19 +1288,26 @@ Autoconf Language
 i.e., expect one level of quotes to be lost.  For instance:

 @example
-AC_COMPILE_IFELSE([char b[10];], [], [AC_MSG_ERROR([you lose])])
+AC_COMPILE_IFELSE(AC_LANG_SOURCE([char b[10];]), [],
+ [AC_MSG_ERROR([you lose])])
 @end example

 @noindent
-is incorrect: here, the first argument of @code{AC_COMPILE_IFELSE} is
+is incorrect: here, the first argument of @code{AC_LANG_SOURCE} is
 @samp{char b[10];} and is expanded once, which results in
address@hidden b10;}.  (There was an idiom common in Autoconf's past to
address@hidden b10;}; and the @code{AC_LANG_SOURCE} is also expanded prior
+to being passed to @code{AC_COMPILE_IFELSE}.  (There was an idiom common
+in Autoconf's past to
 address this issue via the M4 @code{changequote} primitive, but do not
 use it!)  Let's take a closer look: the author meant the first argument
-to be understood as a literal, and therefore it must be quoted twice:
+to be understood as a literal, and therefore it must be quoted twice;
+likewise, the intermediate @code{AC_LANG_SOURCE} macro should be quoted
+once so that it is only expanded after the rest of the body of
address@hidden is in place:

 @example
-AC_COMPILE_IFELSE([[char b[10];]], [], [AC_MSG_ERROR([you lose])])
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[char b[10];]])], [],
+  [AC_MSG_ERROR([you lose])])
 @end example

 @noindent

-- 
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

signature.asc
Description: OpenPGP digital signature