warn about placing of NORET (which is not documented as part of the API

git-svn-id: https://svn.r-project.org/R/trunk@87751 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: ripley

configure

@@ -8095,8 +8095,8 @@ CC_save=${CC}
 CFLAGS_save=${CFLAGS}
 CC_SUB=`echo "${CC}" | sed 's/-std=[^ ]*//'`
 CFLAGS_SUB=`echo "${CFLAGS}" | sed -e 's/-std=[^ ]*//'`
-: ${CC23="${CC_SUB} -std=gnu23"}
 : ${C23FLAGS="${CFLAGS_SUB}"}
+: ${CC23="${CC_SUB}"}
 CC=${CC23}
 CFLAGS=${C23FLAGS}
 unset r_cv_C23
@@ -8149,10 +8149,64 @@ fi
 printf "%s\n" "$r_cv_C23" >&6; }
 
 if test x${r_cv_C23} = xno; then
-unset r_cv_C23
-CC23="${CC_SUB} -std=gnu2x"
-CC=${CC23}
-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether ${CC} is a C23 compiler" >&5
+  ${CC23="${CC_SUB} -std=gnu23"}
+  CC=${CC23}
+  CFLAGS=${C23FLAGS}
+  unset r_cv_C23
+  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether ${CC} is a C23 compiler" >&5
+printf %s "checking whether ${CC} is a C23 compiler... " >&6; }
+if test ${r_cv_C23+y}
+then :
+  printf %s "(cached) " >&6
+else case e in #(
+  e) if test "$cross_compiling" = yes
+then :
+  r_cv_C23=no
+else case e in #(
+  e) cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+#ifdef __STDC_VERSION__
+# if __STDC_VERSION__ < 202000L
+#  error "Compiler does not claim C23 conformance"
+# endif
+#else
+# error "Compiler does not advertise ISO C conformance"
+#endif
+
+// Most new features have feature tests. but bool type is fundamental.
+
+int main(void) {
+     bool x = true;
+
+     return 0;
+}
+
+
+_ACEOF
+if ac_fn_c_try_run "$LINENO"
+then :
+  r_cv_C23=yes
+else case e in #(
+  e) r_cv_C23=no ;;
+esac
+fi
+rm -f core *.core core.conftest.* gmon.out bb.out conftest$ac_exeext \
+  conftest.$ac_objext conftest.beam conftest.$ac_ext ;;
+esac
+fi
+ ;;
+esac
+fi
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $r_cv_C23" >&5
+printf "%s\n" "$r_cv_C23" >&6; }
+
+fi
+if test x${r_cv_C23} = xno; then
+  unset r_cv_C23
+  CC23="${CC_SUB} -std=gnu2x"
+  CC=${CC23}
+  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether ${CC} is a C23 compiler" >&5
 printf %s "checking whether ${CC} is a C23 compiler... " >&6; }
 if test ${r_cv_C23+y}
 then :
@@ -27529,7 +27583,7 @@ _ACEOF
 # flags.
 r_save_CFLAGS=$CFLAGS
 CFLAGS="$CFLAGS $r_verb"
-(eval echo $as_me:27532: \"$ac_link\") >&5
+(eval echo $as_me:27586: \"$ac_link\") >&5
 r_c_v_output=`eval $ac_link 5>&1 2>&1 | grep -v 'Driving:'`
 echo "$r_c_v_output" >&5
 CFLAGS=$r_save_CFLAGS
@@ -27607,7 +27661,7 @@ _ACEOF
 # flags.
 r_save_CFLAGS=$CFLAGS
 CFLAGS="$CFLAGS $r_cv_prog_c_v"
-(eval echo $as_me:27610: \"$ac_link\") >&5
+(eval echo $as_me:27664: \"$ac_link\") >&5
 r_c_v_output=`eval $ac_link 5>&1 2>&1 | grep -v 'Driving:'`
 echo "$r_c_v_output" >&5
 CFLAGS=$r_save_CFLAGS

configure.ac

@@ -756,18 +756,26 @@ CC_save=${CC}
 CFLAGS_save=${CFLAGS}
 CC_SUB=`echo "${CC}" | sed 's/-std=[[^ ]]*//'`
 CFLAGS_SUB=`echo "${CFLAGS}" | sed -e 's/-std=[[^ ]]*//'`
-dnl this is a hack until -std=gnu23 is widely accepted.
-: ${CC23="${CC_SUB} -std=gnu23"}
 : ${C23FLAGS="${CFLAGS_SUB}"}
+dnl first try without a flag for the likes of gcc15
+: ${CC23="${CC_SUB}"}
 CC=${CC23}
 CFLAGS=${C23FLAGS}
 unset r_cv_C23
 R_C23
 if test x${r_cv_C23} = xno; then
-unset r_cv_C23
-CC23="${CC_SUB} -std=gnu2x"
-CC=${CC23}
-R_C23
+  ${CC23="${CC_SUB} -std=gnu23"}
+  CC=${CC23}
+  CFLAGS=${C23FLAGS}
+  unset r_cv_C23
+  R_C23
+fi
+if test x${r_cv_C23} = xno; then
+dnl this is a hack until -std=gnu23 is widely accepted.
+  unset r_cv_C23
+  CC23="${CC_SUB} -std=gnu2x"
+  CC=${CC23}
+  R_C23
 fi
 if test x${r_cv_C23} = xno; then
 CC23=

src/include/R_ext/Error.h

@@ -50,6 +50,13 @@ extern "C" {
  *
  * In C11 there is _Noreturn * (or noreturn in header <stdnoreturn.h>).
  */
+
+/*
+ * As this is sometimes an attribute, it should precede 'static' in a
+ * function declaration.
+ * gcc pre-15 requires it to precede 'attribute_hidden'.
+ * OTOH, '_Noreturn' is an obsolescent (in C23) function specifier.
+ */
 #if defined NORET
 #elif (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202301L)
 # define NORET [[noreturn]]