* NEWS: Documented changes in AC_PROG_CPP and AC_TRY_CPP.

        * doc/autoconf.texi (Compilers and Preprocessors): Likewise.
        * acgeneral.m4 (AC_TRY_CPP): Comment changes.

diff --git a/ChangeLog b/ChangeLog
index 7187c0c5f77c2ee038cb936e2e1d64cf0cb56c69..09cd2c08c16b62694ede79e30efab4f4602c795a 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2000-10-19  Pavel Roskin  <proski@gnu.org>
+
+       * NEWS: Documented changes in AC_PROG_CPP and AC_TRY_CPP.
+       * doc/autoconf.texi (Compilers and Preprocessors): Likewise.
+       * acgeneral.m4 (AC_TRY_CPP): Comment changes.
+
 2000-10-19  Pavel Roskin  <proski@gnu.org>
 
        * doc/autoconf.texi (Shellology): Documented quirks in ash-0.2.

diff --git a/NEWS b/NEWS
index edda2df64827517f4e4fdf32044e3838c2f9d196..bc3d5b0973c7d47af7bff2e64b41aaec05c6e0f3 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -191,6 +191,10 @@ test cases in this new frame work.
   Checks if the compiler supports ISO C, included when needs special
   options.
 
+- AC_PROG_CPP
+  Checking whether the preprocessor indicates missing includes by the
+  error code. stderr is checked by AC_TRY_CPP only as a fallback.
+
 - AC_LANG
   Takes a language as argument and replaces AC_LANG_C,
   AC_LANG_CPLUSPLUS and AC_LANG_FORTRAN77.

diff --git a/acgeneral.m4 b/acgeneral.m4
index b54c6d669484c2b616157452c8878b59425ec0c6..4f6a78fc3f1a1c1e91df21a36dfb9ce523acd7a2 100644 (file)
--- a/acgeneral.m4
+++ b/acgeneral.m4
@@ -3389,10 +3389,9 @@ fi
 
 # AC_TRY_CPP(INCLUDES, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
 # ---------------------------------------------------------
-# Capture the stderr of cpp.  eval is necessary to expand ac_cpp.  We
-# used to copy stderr to stdout and capture it in a variable, but that
-# breaks under sh -x, which writes compile commands starting with ` +'
-# to stderr in eval and subshells.
+# AC_TRY_CPP is used to check whether particular header files exist.
+# You can check for one at a time, or more than one if you need several
+# header files to all exist for some purpose.
 #
 # INCLUDES are not defaulted.
 AC_DEFUN([AC_TRY_CPP],

diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index b25ab60fe9a1dc40d7acf4cb3145b4d6eddf3870..92cd48840535cce6fc98817c3f421cfd0cdeb928 100644 (file)
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -4057,7 +4057,7 @@ using the program @code{ansi2knr}, which comes with Automake.
 @maindex PROG_CPP
 @ovindex CPP
 Set output variable @code{CPP} to a command that runs the
-C preprocessor.  If @samp{$CC -E} doesn't work, it uses @file{/lib/cpp}.
+C preprocessor.  If @samp{$CC -E} doesn't work, @file{/lib/cpp} is used.
 It is only portable to run @code{CPP} on files with a @file{.c}
 extension.
 
@@ -4065,6 +4065,11 @@ If the current language is C (@pxref{Language Choice}), many of the
 specific test macros use the value of @code{CPP} indirectly by calling
 @code{AC_TRY_CPP}, @code{AC_CHECK_HEADER}, @code{AC_EGREP_HEADER}, or
 @code{AC_EGREP_CPP}.
+
+Some preprocessors don't indicate missing include files by the error
+status.  For such preprocessors an internal variable is set that causes
+other macros to check the standard error from the preprocessor and
+consider the test failed if any warnings have been reported.
 @end defmac
 
 @defmac AC_PROG_CXX (@ovar{compiler-search-list})
@@ -4102,7 +4107,7 @@ compilers.
 @maindex PROG_CXXCPP
 @ovindex CXXCPP
 Set output variable @code{CXXCPP} to a command that runs the C++
-preprocessor.  If @samp{$CXX -E} doesn't work, it uses @file{/lib/cpp}.
+preprocessor.  If @samp{$CXX -E} doesn't work, @file{/lib/cpp} is used.
 It is only portable to run @code{CXXCPP} on files with a @file{.c},
 @file{.C}, or @file{.cc} extension.
 
@@ -4110,6 +4115,12 @@ If the current language is C++ (@pxref{Language Choice}), many of the
 specific test macros use the value of @code{CXXCPP} indirectly by
 calling @code{AC_TRY_CPP}, @code{AC_CHECK_HEADER},
 @code{AC_EGREP_HEADER}, or @code{AC_EGREP_CPP}.
+
+Some preprocessors don't indicate missing include files by the error
+status.  For such preprocessors an internal variable is set that causes
+other macros to check the standard error from the preprocessor and
+consider the test failed if any warnings have been reported.  However,
+it is not known whether such broken preprocessors exist for C++.
 @end defmac
 
 @defmac AC_PROG_F77 (@ovar{compiler-search-list})

diff --git a/lib/autoconf/general.m4 b/lib/autoconf/general.m4
index b54c6d669484c2b616157452c8878b59425ec0c6..4f6a78fc3f1a1c1e91df21a36dfb9ce523acd7a2 100644 (file)
--- a/lib/autoconf/general.m4
+++ b/lib/autoconf/general.m4
@@ -3389,10 +3389,9 @@ fi
 
 # AC_TRY_CPP(INCLUDES, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
 # ---------------------------------------------------------
-# Capture the stderr of cpp.  eval is necessary to expand ac_cpp.  We
-# used to copy stderr to stdout and capture it in a variable, but that
-# breaks under sh -x, which writes compile commands starting with ` +'
-# to stderr in eval and subshells.
+# AC_TRY_CPP is used to check whether particular header files exist.
+# You can check for one at a time, or more than one if you need several
+# header files to all exist for some purpose.
 #
 # INCLUDES are not defaulted.
 AC_DEFUN([AC_TRY_CPP],