More is_constant_evaluated tweaks/fixes.

doc/html/boost_config/boost_macro_reference.html

@@ -4544,7 +4544,14 @@
                   when the current context is <code class="computeroutput"><span class="keyword">constexpr</span></code>
                   and false otherwise. This macro may be functional in C++14 onwards
                   if the compiler has a suitable intrinsic we recognise (MSVC/Clang/GCC
-                  are currently supported). The macro always evaluates to <code class="computeroutput"><span class="keyword">false</span></code> on unsupported/old compilers.
+                  are currently supported).
+                </p>
+                <p>
+                  Note that before using this macro, the program must include <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">type_traits</span><span class="special">&gt;</span></code>.
+                </p>
+                <p>
+                  The macro always evaluates to <code class="computeroutput"><span class="keyword">false</span></code>
+                  on unsupported/old compilers.
                 </p>
               </td>
 </tr>
@@ -4561,8 +4568,20 @@
                   The macro may be functional in C++14 onwards if the compiler has
                   a suitable intrinsic, in particular this macro is functional for
                   gcc-6 and onwards as well as for compilers which have direct support
-                  for <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">is_constant_evaluated</span></code>. The macro
+                  for <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">is_constant_evaluated</span></code>.
-                  always evaluates to <code class="computeroutput"><span class="keyword">false</span></code>
+                </p>
+                <p>
+                  Note that before using this macro, the program must include <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">type_traits</span><span class="special">&gt;</span></code>.
+                </p>
+                <p>
+                  Note that this macro may behave subtly different from <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">is_constant_evaluated</span><span class="special">()</span></code>
+                  in that it may evaluate to <code class="computeroutput"><span class="keyword">true</span></code>
+                  when code is evaluated in a non-constexpr context, but is none
+                  the less evaluated at "compile time" as a result of program
+                  optimisation.
+                </p>
+                <p>
+                  The macro always evaluates to <code class="computeroutput"><span class="keyword">false</span></code>
                   on unsupported/old compilers.
                 </p>
               </td>

doc/html/index.html

@@ -996,7 +996,7 @@
 </div>
 </div>
 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
-<td align="left"><p><small>Last revised: August 08, 2021 at 18:21:47 GMT</small></p></td>
+<td align="left"><p><small>Last revised: August 09, 2021 at 18:40:57 GMT</small></p></td>
 <td align="right"><div class="copyright-footer"></div></td>
 </tr></table>
 <hr>

doc/macro_reference.qbk

@@ -1088,10 +1088,20 @@ that are not yet supported by a particular compiler or library.
 [[macro][Description]]
 [[`BOOST_IS_CONSTANT_EVALUATED()`][Evaluated to `true` when the current context is `constexpr` and false otherwise.
                                  This macro may be functional in C++14 onwards if the compiler has a suitable intrinsic we recognise (MSVC/Clang/GCC are currently supported).
+
+                                 Note that before using this macro, the program must include `<type_traits>`.
+
                                  The macro always evaluates to `false` on unsupported/old compilers.]]
 [[`BOOST_IS_CONSTANT_EVALUATED_INT(integer-expression)`][Evaluates to `true` when `integer-expression` is `constexpr`.
                                  The macro may be functional in C++14 onwards if the compiler has a suitable intrinsic, in particular this macro is functional for gcc-6 and onwards
                                  as well as for compilers which have direct support for `std::is_constant_evaluated`.
+
+                                 Note that before using this macro, the program must include `<type_traits>`.
+
+                                 Note that this macro may behave subtly different from `std::is_constant_evaluated()` in that it may evaluate to
+                                 `true` when code is evaluated in a non-constexpr context, but is none the less evaluated at "compile time" as a result
+                                 of program optimisation.
+
                                  The macro always evaluates to `false` on unsupported/old compilers.]]
 [[BOOST_IS_CONSTANT_EVALUATED_VERSION][Evaluates to 0 if there is no support for this feature, 1 if `BOOST_IS_CONSTANT_EVALUATED_INT` is fully functional, and 2 if both
                                  BOOST_IS_CONSTANT_EVALUATED_INT and BOOST_IS_CONSTANT_EVALUATED are fully functional.]]

include/boost/config/detail/suffix.hpp

@@ -1094,7 +1094,7 @@ namespace std{ using ::type_info; }
 #  define BOOST_IS_CONSTANT_EVALUATED_INT(integer) BOOST_CONFIG_IS_CONST_EVALUATED_INT(integer)
 #  define BOOST_IS_CONSTANT_EVALUATED_VERSION 1
 #else
-#  define BOOST_IS_CONSTANT_EVALUATED false
+#  define BOOST_IS_CONSTANT_EVALUATED_INT(i) false
 #endif
 
 #ifndef BOOST_IS_CONSTANT_EVALUATED_VERSION

test/test_boost_is_constant_evaluated.cpp

@@ -7,6 +7,7 @@
 
 #ifndef BOOST_NO_CXX11_HDR_TYPE_TRAITS
 #include <type_traits>
+#include <cstdlib>
 
 #if BOOST_IS_CONSTANT_EVALUATED_VERSION >= 2
 inline constexpr int factorial1(int i)