dnl @synopsis VL_PROG_CC_WARNINGS([ANSI])
dnl
dnl Enables a reasonable set of warnings for the C compiler.  Optionally,
dnl if the first argument is nonempty, turns on flags which enforce and/or
dnl enable proper ANSI C if such are known with the compiler used.
dnl
dnl Currently this macro knows about GCC, Solaris C compiler,
dnl Digital Unix C compiler, C for AIX Compiler, HP-UX C compiler,
dnl IRIX C compiler, NEC SX-5 (Super-UX 10) C compiler, and Cray J90
dnl (Unicos 10.0.0.8) C compiler.
dnl
dnl @version 1.1
dnl @author Ville Laurikari <vl@iki.fi>
dnl
AC_DEFUN([VL_PROG_CC_WARNINGS], [
  ansi=$1
  if test -z "$ansi"; then
    msg="for C compiler warning flags"
  else
    msg="for C compiler warning and ANSI conformance flags"
  fi
  AC_CACHE_CHECK($msg, vl_cv_prog_cc_warnings, [
    if test -n "$CC"; then
      cat > conftest.c <<EOF
int main(int argc, char **argv) { return 0; }
EOF

      dnl GCC
      if test "$GCC" = "yes"; then
        if test -z "$ansi"; then
          vl_cv_prog_cc_warnings="-fno-common -Wall -Wpointer-arith -Wstrict-prototypes -Wformat -Wformat-security"
        else
          vl_cv_prog_cc_warnings="-fno-common -Wall -ansi -pedantic -Wpointer-arith -Wstrict-prototypes"
        fi

      dnl Most compilers print some kind of a version string with some command
      dnl line options (often "-V").  The version string should be checked
      dnl before doing a test compilation run with compiler-specific flags.
      dnl This is because some compilers (like the Cray compiler) only
      dnl produce a warning message for unknown flags instead of returning
      dnl an error, resulting in a false positive.  Also, compilers may do
      dnl erratic things when invoked with flags meant for a different
      dnl compiler.

      dnl Solaris C compiler
      elif $CC -V 2>&1 | grep -i "WorkShop" > /dev/null 2>&1 &&
           $CC -c -v -Xc conftest.c > /dev/null 2>&1 &&
           test -f conftest.o; then
        if test -z "$ansi"; then
          vl_cv_prog_cc_warnings="-v"
        else
          vl_cv_prog_cc_warnings="-v -Xc"
        fi

      dnl Digital Unix C compiler
      elif $CC -V 2>&1 | grep -i "Digital UNIX Compiler" > /dev/null 2>&1 &&
           $CC -c -verbose -w0 -warnprotos -std1 conftest.c > /dev/null 2>&1 &&
           test -f conftest.o; then
        if test -z "$ansi"; then
          vl_cv_prog_cc_warnings="-verbose -w0 -warnprotos"
        else
          vl_cv_prog_cc_warnings="-verbose -w0 -warnprotos -std1"
        fi

      dnl C for AIX Compiler
      elif $CC 2>&1 | grep -i "C for AIX Compiler" > /dev/null 2>&1 &&
           $CC -c -qlanglvl=ansi -qinfo=all conftest.c > /dev/null 2>&1 &&
           test -f conftest.o; then
        if test -z "$ansi"; then
          vl_cv_prog_cc_warnings="-qsrcmsg -qinfo=all:noppt:noppc:noobs:nocnd"
        else
          vl_cv_prog_cc_warnings="-qsrcmsg -qinfo=all:noppt:noppc:noobs:nocnd -qlanglvl=ansi"
        fi

      dnl IRIX C compiler
      elif $CC -version 2>&1 | grep -i "MIPSpro Compilers" > /dev/null 2>&1 &&
           $CC -c -fullwarn -ansi -ansiE conftest.c > /dev/null 2>&1 &&
           test -f conftest.o; then
        if test -z "$ansi"; then
          vl_cv_prog_cc_warnings="-fullwarn"
        else
          vl_cv_prog_cc_warnings="-fullwarn -ansi -ansiE"
        fi

      dnl HP-UX C compiler
      elif what $CC 2>&1 | grep -i "HP C Compiler" > /dev/null 2>&1 &&
           $CC -c -Aa +w1 conftest.c > /dev/null 2>&1 &&
           test -f conftest.o; then
        if test -z "$ansi"; then
          vl_cv_prog_cc_warnings="+w1"
        else
          vl_cv_prog_cc_warnings="+w1 -Aa"
        fi

      dnl The NEC SX-5 (Super-UX 10) C compiler
      elif $CC -V 2>&1 | grep "/SX" > /dev/null 2>&1 &&
           $CC -c -pvctl[,]fullmsg -Xc conftest.c > /dev/null 2>&1 &&
           test -f conftest.o; then
        if test -z "$ansi"; then
          vl_cv_prog_cc_warnings="-pvctl[,]fullmsg"
        else
          vl_cv_prog_cc_warnings="-pvctl[,]fullmsg -Xc"
        fi

      dnl The Cray C compiler (Unicos)
      elif $CC -V 2>&1 | grep -i "Cray" > /dev/null 2>&1 &&
           $CC -c -h msglevel 2 conftest.c > /dev/null 2>&1 &&
           test -f conftest.o; then
        if test -z "$ansi"; then
          vl_cv_prog_cc_warnings="-h msglevel 2"
        else
          vl_cv_prog_cc_warnings="-h msglevel 2 -h conform"
        fi

      fi
      rm -f conftest.*
    fi
    if test -n "$vl_cv_prog_cc_warnings"; then
      CFLAGS="$CFLAGS $vl_cv_prog_cc_warnings"
    else
      vl_cv_prog_cc_warnings="unknown"
    fi
  ])
])dnl