make sure Boolean.h finds bool type

git-svn-id: https://svn.r-project.org/R/trunk@87842 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: ripley

doc/NEWS.Rd

@@ -348,8 +348,12 @@
       unaware of any such platform).
 
       \item There is a new function \code{asRboolean}, a variannt of
-      \code{asLogical} more suitable to converting logical arguments to
+      \code{asLogical} more suited to converting logical arguments to
       \code{Rboolean}.
+
+      \item Header \file{R_ext/Boolean.h} now ensures a \code{bool} type
+      is available either as a keyword (C23 and C++) or by including the
+      C99 header \file{stdbool.h}.
     }
   }
 

src/include/R_ext/Boolean.h

@@ -29,6 +29,19 @@
 #undef FALSE
 #undef TRUE
 
+/* Ensuure a 'bool' type is available.  We could use
+   __bool_true_false_are_defined, 
+   but that was declared obsolescent in C23.
+*/
+#if defined __STDC_VERSION__ && __STDC_VERSION__ > 202000L
+// C23 so bool is a keyword
+#elif defined __cplusplus
+// part of C++ >= 11, which is all R supports.
+#else
+# include <stdbool.h>
+// stdbool.h is C99, so available everywhere.
+#endif
+
 #include <Rconfig.h> /* for HAVE_ENUM_BASE_TYPE */
 /*
   Setting the underlying aka base type is supported in C23, C++11