use fixed-type emum where supported

git-svn-id: https://svn.r-project.org/R/trunk@87798 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: ripley

doc/NEWS.Rd

@@ -6,11 +6,11 @@
 \encoding{UTF-8}
 
 \section{\Rlogo CHANGES IN R-devel}{
-  \subsection{SIGNIFICANT USER-VISIBLE CHANGES}{
-    \itemize{
-      \item .
-    }
-  }
+  %% \subsection{SIGNIFICANT USER-VISIBLE CHANGES}{
+  %%   \itemize{
+  %%     \item .
+  %%   }
+  %% }
 
   \subsection{NEW FEATURES}{
     \itemize{
@@ -330,6 +330,21 @@
       \item The deprecated and seemingly never-used S-compatibility
       macros \code{F77_COM} and \code{F77_COMDECL} have been removed
       from header \file{R_ext/RS.h}.
+
+      \item The \code{enum} \code{Rboolean} defined in header
+      \file{R_ext/Boolean.h} now has a fixed underlying type of
+      \code{int} on platforms whose C compiler supports this.
+
+      This is a C23 feature (taken from C++11) and also supported in all
+      C standards by some versions of \code{clang} (from \I{LLVM} and
+      Apple).
+
+      A fair amount of code has assumed this: it may be changed to a
+      smaller type in future.
+
+      If there were a platform which used an underlying type of a
+      different size this would be an ABI-breaking change (but we are
+      unaware of any such platform).
     }
   }
 
@@ -613,8 +628,10 @@
       \I{Benjamin Sommer}'s report in \PR{18861} and collaboration with
       \I{Heather Turner} improving \code{reformulate()}.
 
-      \item Arguments which should be length-1 logical,
-      e.g.\sspace{}\code{min(na.rm =)}, are checked more thoroughly.
+      \item Arguments which should be length-1 logical are checked more
+      thoroughly.  The most commonly seen errors are in \code{unlink(,
+      recursive)}, \code{tempdir()} and the \code{na.rm} argument of
+      \code{max()}, \code{min()}, \code{sum()}, \dots.
     }
   }
 }

src/include/R_ext/Boolean.h

@@ -29,10 +29,31 @@
 #undef FALSE
 #undef TRUE
 
+#include <Rconfig.h> /* for HAVE_ENUM_BASE_TYPE */
+/*
+  Setting the underlying aka base type is supported in C23, C++11 
+  and some C compilers based on clang.
+  What matters here is the C compiler used to build R.
+ */
 #ifdef  __cplusplus
 extern "C" {
 #endif
+#ifdef HAVE_ENUM_BASE_TYPE
+// Apple clang warns even in C23 mode: gcc warns about #pragma clang
+// LLVM clang no linger warns: we have no good way to filter Apple clang.
+# if defined  __APPLE__ && defined __clang__
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Wfixed-enum-extension"
+# endif
+
+  typedef enum :int { FALSE = 0, TRUE } Rboolean;  // so NOT NA
+
+# if defined  __APPLE__ && defined __clang__
+#  pragma clang diagnostic pop
+# endif
+#else
     typedef enum { FALSE = 0, TRUE } Rboolean;  // so NOT NA
+#endif
 #ifdef  __cplusplus
 }
 #endif