vcpkg/ports/boost-cmake/add-optional-deps.diff

diff --git a/include/BoostRoot.cmake b/include/BoostRoot.cmake
index f356666739..1843f528cd 100644
--- a/include/BoostRoot.cmake	
+++ b/include/BoostRoot.cmake
@@ -189,6 +189,7 @@ function(__boost_scan_dependencies lib var)
 
   set(result "")
   set(required_components "")
+  set(optional_components "")
 
   if(EXISTS "${BOOST_SUPERPROJECT_SOURCE_DIR}/libs/${lib}/CMakeLists.txt")
 
@@ -202,6 +203,12 @@ function(__boost_scan_dependencies lib var)
         string(REGEX REPLACE "^numeric_" "numeric/" dep ${CMAKE_MATCH_1})
         list(APPEND result ${dep})
 
+      elseif(line MATCHES "^[ ]*\\$<TARGET_NAME_IF_EXISTS:Boost::([A-Za-z0-9_]+)>[ ]*$")
+
+        list(APPEND optional_components ${CMAKE_MATCH_1})
+        string(REGEX REPLACE "^numeric_" "numeric/" dep ${CMAKE_MATCH_1})
+        list(APPEND result ${dep})
+
       endif()
 
     endforeach()
@@ -209,9 +216,10 @@ function(__boost_scan_dependencies lib var)
   endif()
 
   list(REMOVE_DUPLICATES required_components)
+  list(REMOVE_DUPLICATES optional_components)
   list(REMOVE_ITEM required_components boost ${lib}) # due to property_tree and python
-  if(required_components)
+  if(required_components OR optional_components)
-    find_package(Boost COMPONENTS ${required_components} REQUIRED CONFIG)
+    find_package(Boost COMPONENTS ${required_components} OPTIONAL_COMPONENTS ${optional_components} REQUIRED CONFIG)
   endif()
   set(${var} ${result} PARENT_SCOPE)