Some documentation changes regarding CPP

[Pavel Roskin]

Hello!

As requested:

ChangeLog:
        * 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.

_________________________________
Index: NEWS
--- NEWS        Tue Oct 17 17:02:14 2000
+++ NEWS        Thu Oct 19 16:09:11 2000
@@ -191,6 +191,10 @@
   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.
Index: acgeneral.m4
--- acgeneral.m4        Wed Oct 18 17:34:39 2000
+++ acgeneral.m4        Thu Oct 19 16:01:30 2000
@@ -3389,10 +3389,9 @@
 
 # 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],
Index: doc/autoconf.texi
--- doc/autoconf.texi   Wed Oct 18 17:34:39 2000
+++ doc/autoconf.texi   Thu Oct 19 15:52:47 2000
@@ -4057,7 +4057,7 @@
 @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 @@
 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 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 @@
 @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 @@
 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 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})
_________________________________

Regards,
Pavel Roskin