[SCM] GNU Autoconf source repository branch, master, updated. v2.63-145-gcd9fbb8

[Eric Blake]

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- Log -----------------------------------------------------------------
commit cd9fbb8453739ef795a6a64192610265d49577d2
Author: Eric Blake <address@hidden>
Date:   Thu Oct 30 22:05:55 2008 -0600

    Better documentation of AC_CHECK_HEADER's fourth argument.
    
    * doc/autoconf.texi (Generic Headers) <AC_CHECK_HEADER>: Mention
    how to suppress compiler or preprocessor header check.
    Reported by Jeff Squyres.
    
    Signed-off-by: Eric Blake <address@hidden>

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog         |    7 +++++++
 doc/autoconf.texi |   27 +++++++++++++++++++--------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 457d711..d1c89f9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 2008-10-30  Eric Blake  <address@hidden>
 
+       Better documentation of AC_CHECK_HEADER's fourth argument.
+       * doc/autoconf.texi (Generic Headers) <AC_CHECK_HEADER>: Mention
+       how to suppress compiler or preprocessor header check.
+       Reported by Jeff Squyres.
+
+2008-10-30  Eric Blake  <address@hidden>
+
        Fix LINENO testsuite failure.
        * tests/m4sh.at (AT_DATA_LINENO): Use AS_LINENO_PREPARE, not
        undocumented _AS_PREPARE, and move unset earlier in script.
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index f10eeae..35c9bfa 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -5795,7 +5795,7 @@ test for it (@pxref{Writing Tests}).
 
 @anchor{AC_CHECK_HEADER}
 @defmac AC_CHECK_HEADER (@var{header-file}, @ovar{action-if-found}, @
-  @ovar{action-if-not-found}, @dvar{includes, AC_INCLUDES_DEFAULT})
+  @ovar{action-if-not-found}, @ovar{includes})
 @acindex{CHECK_HEADER}
 If the system header file @var{header-file} is compilable, execute shell
 commands @var{action-if-found}, otherwise execute
@@ -5803,9 +5803,20 @@ commands @var{action-if-found}, otherwise execute
 header file is available, consider using @code{AC_CHECK_HEADERS}
 instead.
 
address@hidden is a series of include directives, defaulting to
address@hidden (@pxref{Default Includes}), which are used
-prior to the header under test.
address@hidden is decoded to determine the appropriate include
+directives.  If omitted, @file{configure} will check for both header
+existence (with the preprocessor) and usability (with the compiler),
+using @code{AC_INCLUDES_DEFAULT} for the compile test.  Currently, if
+there is a discrepancy between the results, a warning is issued to the
+user, and the preprocessor results are favored (@pxref{Present But
+Cannot Be Compiled}); but a future release may switch to favoring the
+compiler results.  If @var{includes} is exactly @samp{-}, then only a
+preprocessor check is performed, without regard to prerequisite headers.
+For anything else, only a compiler check is performed, using
address@hidden as the set of preprocessor directives to use prior to
+including the header under test, in which case, it is common to manually
+list @code{AC_INCLUDES_DEFAULT} (@pxref{Default Includes}) along with
+any other prerequisite headers.
 
 For compatibility issues with older versions of Autoconf, please read
 below.
@@ -5814,7 +5825,7 @@ below.
 @anchor{AC_CHECK_HEADERS}
 @defmac AC_CHECK_HEADERS (@address@hidden, @
   @ovar{action-if-found}, @ovar{action-if-not-found}, @
-  @dvar{includes, AC_INCLUDES_DEFAULT})
+  @ovar{includes})
 @acindex{CHECK_HEADERS}
 @cvindex address@hidden
 For each given system header file @var{header-file} in the
@@ -5825,9 +5836,9 @@ files is found.  You can give it a value of @samp{break} 
to break out of
 the loop on the first match.  If @var{action-if-not-found} is given, it
 is executed when one of the header files is not found.
 
address@hidden is a series of include directives, defaulting to
address@hidden (@pxref{Default Includes}), which are used
-prior to the headers under test.
address@hidden is interpreted as in @code{AC_CHECK_HEADER}, in order to
+choose the set of preprocessor directives supplied before the header
+under test.
 
 For compatibility issues with older versions of Autoconf, please read
 below.


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