Big clean up to fix issues identified by the inspect program.

Regenerate docs.

doc/html/boost_config/boost_macro_reference.html

@@ -3832,6 +3832,18 @@
               </td>
 </tr>
 <tr>
+<td>
+                <p>
+                  <code class="computeroutput"><span class="identifier">BOOST_NO_CXX17_HDR_VARIANT</span></code>
+                </p>
+              </td>
+<td>
+                <p>
+                  The compiler does not support the header <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">variant</span><span class="special">&gt;</span></code>.
+                </p>
+              </td>
+</tr>
+<tr>
 <td>
                 <p>
                   <code class="computeroutput"><span class="identifier">BOOST_NO_CXX17_HDR_STRING_VIEW</span></code>
@@ -4567,6 +4579,33 @@
               </td>
 </tr>
 <tr>
+<td>
+                <p>
+                  <code class="computeroutput"><span class="identifier">BOOST_ATTRIBUTE_NODISCARD</span></code>
+                </p>
+              </td>
+<td>
+                <p>
+                  Expands to <code class="computeroutput"><span class="special">[[</span><span class="identifier">nodiscard</span><span class="special">]]</span></code> when this is available - can
+                  be used to create a warning when a type or variable is unused.
+                </p>
+              </td>
+</tr>
+<tr>
+<td>
+                <p>
+                  <code class="computeroutput"><span class="identifier">BOOST_ATTRIBUTE_NO_UNIQUE_ADDRESS</span></code>
+                </p>
+              </td>
+<td>
+                <p>
+                  Expands to <code class="computeroutput"><span class="special">[[</span><span class="identifier">no_unique_address</span><span class="special">]]</span></code> when this is available - can
+                  be used to indicate that a non-static data member need not have
+                  a unique address (for example empty classes).
+                </p>
+              </td>
+</tr>
+<tr>
 <td>
                 <p>
                   <code class="computeroutput"><span class="identifier">BOOST_MAY_ALIAS</span></code>,

doc/html/boost_config/build_config.html

@@ -104,7 +104,8 @@
       Notice that multiple arguments can be added to the requires rule, and that
       these are always the same as the Boost.Config macro name, but in lower case
       and with the <span class="emphasis"><em>boost_no_</em></span> or <span class="emphasis"><em>boost_has_</em></span>
-      prefix removed.
+      prefix removed. You can also use any C++ standard feature-macro name with the
+      leading underscores removed (see more below).
     </p>
 <p>
       When building the above example, you will see at the start of the build process
@@ -114,6 +115,36 @@
 <span class="special">-</span> <span class="identifier">Boost</span><span class="special">.</span><span class="identifier">Config</span> <span class="identifier">Feature</span> <span class="identifier">Check</span><span class="special">:</span> <span class="identifier">cxx11_constexpr</span> <span class="special">:</span> <span class="identifier">yes</span>
 <span class="special">-</span> <span class="identifier">Boost</span><span class="special">.</span><span class="identifier">Config</span> <span class="identifier">Feature</span> <span class="identifier">Check</span><span class="special">:</span> <span class="identifier">cxx11_user_defined_literals</span> <span class="special">:</span> <span class="identifier">yes</span>
 </pre>
+<p>
+      If you wish to make a build conditional on a C++ standard feature macro then
+      you can specify these too, just remove the leading underscores from the name.
+      For example:
+    </p>
+<pre class="programlisting"><span class="special">[</span> <span class="identifier">requires</span> <span class="identifier">cpp_constexpr</span> <span class="special">]</span>
+</pre>
+<p>
+      To require C++11 style const-expressions. If you want to specify a macro from
+      a particular standard, then you append an underscore followed by the (2 digit)
+      year of the standard, for example:
+    </p>
+<pre class="programlisting"><span class="special">[</span> <span class="identifier">requires</span> <span class="identifier">cpp_constexpr_17</span> <span class="special">]</span>
+</pre>
+<p>
+      For C++17 constepxr. If you don't specify a standard then you get the first
+      version that introduced the macro. In addition there are only standard-specific
+      rules for each version bump of the macro, so:
+    </p>
+<pre class="programlisting"><span class="special">[</span> <span class="identifier">requires</span> <span class="identifier">cpp_if_constexpr_17</span> <span class="special">]</span>
+</pre>
+<p>
+      Is fine since the macro was introduced in C++17 and is the same as the un-versioned
+      name, but:
+    </p>
+<pre class="programlisting"><span class="special">[</span> <span class="identifier">requires</span> <span class="identifier">cpp_if_constexpr_20</span> <span class="special">]</span>
+</pre>
+<p>
+      Will result in a build error since there is no C++20 version bump for <code class="computeroutput"><span class="identifier">__cpp_if_constexpr</span></code>.
+    </p>
 <p>
       That's all there is to this handy feature, should at any time you be unsure
       of the feature-test names you can pass to the "requires" rule, then

doc/html/index.html

@@ -969,11 +969,6 @@
         files, there are rather a lot of them, so there are a couple of shortcuts
         to help you out:
       </p>
-<p>
-        If you have built the <a href="../../../../tools/regression/doc/index.html" target="_top">boost
-        regression test driver</a>, then you can use this to produce a nice html
-        formatted report of the results using the supplied test file.
-      </p>
 <p>
         Alternatively you can run the configure script like this:
       </p>
@@ -993,7 +988,7 @@
 </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: October 15, 2018 at 16:56:00 GMT</small></p></td>
+<td align="left"><p><small>Last revised: August 20, 2019 at 17:48:08 GMT</small></p></td>
 <td align="right"><div class="copyright-footer"></div></td>
 </tr></table>
 <hr>