add R_INCLUDE_BOOLEAN_H=0

git-svn-id: https://svn.r-project.org/R/trunk@88052 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: ripley

doc/NEWS.Rd

@@ -45,6 +45,7 @@
       also seen for \code{nullptr} (C23 and C++11). Masking these by
       macros \emph{may} generate correct code (but not always) and always
       results in confusing-to-read code.
+      %% Someone defined 'true' as -1, for example.
     }
   }
 
@@ -504,6 +505,17 @@
       declaration for \code{F77_SUB(interv)}.  This is intended to be
       called from Fortran and was wrongly declared: \code{LOGICAL} in
       Fortran corresponds to \code{int *} not \code{Rboolean *}.
+
+      \item Defining \code{R_INCLUDE_BOOLEAN_H} to \code{0} before
+      including headers \file{R.h} or \file{Rinternals.h} (or any other
+      header which includes \file{R_ext/Boolean.h}) stops the inclusion
+      of header \code{R_ext/Boolean.h} which `defines' constants
+      \code{TRUE}, \code{true}, \code{false} and the type \code{bool}
+      which some package maintainers wish to avoid.
+
+      Note that the last three are keywords in C23 and C++11 so cannot be
+      avoided entirely.  However, with commonly-used compilers they can be
+      masked by a macro of the same name, often with a warning.
     }
   }
 

src/include/R_ext/Boolean.h

@@ -25,6 +25,7 @@
 
 #ifndef R_EXT_BOOLEAN_H_
 #define R_EXT_BOOLEAN_H_
+#if !defined(R_INCLUDE_BOOLEAN_H) || R_INCLUDE_BOOLEAN_H
 
 // NB: there is a version of this in Rmath.h0[.in]
 
@@ -73,4 +74,12 @@ extern "C" {
 }
 #endif
 
+#else
+/* The Rbolean type is used in too many R headers to condition them
+ * all.  However, people defining R_INCLUDE_BOOLEAN_H=0 should not be
+ * using it in their own code, and its base type is expected to be int
+ * (and guaranteed to be on most platforms as from R 4.5.0). */
+
+    typedef Rboolean int;
+#endif /* R_INCLUDE_BOOLEAN_H = 0 */
 #endif /* R_EXT_BOOLEAN_H_ */