Disable installation without the superproject; add comments

CMakeLists.txt

@@ -3,24 +3,28 @@
 # Distributed under the Boost Software License, Version 1.0.
 # See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt
 
+# We support CMake 3.5, but prefer 3.16 policies and behavior
 cmake_minimum_required(VERSION 3.5...3.16)
-project(BoostTypeTraits VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
+
+project(boost_type_traits VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
 
 add_library(boost_type_traits INTERFACE)
 add_library(Boost::type_traits ALIAS boost_type_traits)
 
 target_include_directories(boost_type_traits INTERFACE include)
 
 target_link_libraries(boost_type_traits
-    INTERFACE
-        Boost::config
-        Boost::static_assert
+  INTERFACE
+    Boost::config
+    Boost::static_assert
 )
 
-include(BoostInstall OPTIONAL RESULT_VARIABLE HAVE_BOOST_INSTALL)
+# boost_install requires PROJECT_VERSION
+# Without the superproject, we don't have any, so skip installation
 
-if(HAVE_BOOST_INSTALL)
+if(BOOST_SUPERPROJECT_VERSION)
 
-    boost_install(TARGETS boost_type_traits HEADER_DIRECTORY include/)
+  include(BoostInstall)
+  boost_install(TARGETS boost_type_traits HEADER_DIRECTORY include/)
 
 endif()