Speed improvement with CGAL_HEADER_ONLY and WITH_{tests|examples}..

When `CGAL_HEADER_ONLY` and `WITH_{examples|tests|demos}`, then only
the first call to `find_package(CGAL)` does the job. The subsequent
calls return very fast, by caching the results in global properties.

Installation/CMakeLists.txt

@@ -805,6 +805,16 @@ cache_get(CGAL_3RD_PARTY_LIBRARIES_DIRS)
 
 add_subdirectory(src)
 
+#
+# Variables used when WITH_{demos|examples|tests} are TRUE, and
+# CGAL_HEADER_ONLY=ON
+#
+set(CGAL_USE_FILE ${CGAL_MODULES_DIR}/UseCGAL.cmake)
+get_property(CGAL_FOUND GLOBAL PROPERTY CGAL_FOUND)
+get_property(CGAL_Core_FOUND GLOBAL PROPERTY CGAL_Core_FOUND)
+get_property(CGAL_ImageIO_FOUND GLOBAL PROPERTY CGAL_ImageIO_FOUND)
+get_property(CGAL_Qt5_FOUND GLOBAL PROPERTY CGAL_Qt5_FOUND)
+
 #
 # Repeat some problems
 #

Installation/cmake/modules/CGAL_SetupCGALDependencies.cmake

@@ -60,6 +60,7 @@ include(${CMAKE_CURRENT_LIST_DIR}/CGAL_SetupBoost.cmake)
 #    Set to `TRUE` if the dependencies of CGAL were found.
 if(Boost_FOUND)
   set(CGAL_FOUND TRUE)
+  set_property(GLOBAL PROPERTY CGAL_FOUND TRUE)
 endif()
 
 #.rst:

Installation/cmake/modules/CGAL_SetupCGAL_CoreDependencies.cmake

@@ -33,6 +33,7 @@ if(NOT CGAL_DISABLE_GMP)
   include(${CMAKE_CURRENT_LIST_DIR}/CGAL_SetupGMP.cmake)
   if(GMP_FOUND)
     set(CGAL_Core_FOUND TRUE)
+    set_property(GLOBAL PROPERTY CGAL_Core_FOUND TRUE)
   endif()
 endif()
 
@@ -52,18 +53,19 @@ endif()
 #   keyword, or ``PUBLIC`` otherwise.
 #
 
-# See the release notes of CGAL-4.10: CGAL_Core now requires
-# Boost.Thread, with all compilers but MSVC.
-if (NOT MSVC)
-  find_package( Boost 1.48 REQUIRED thread system )
-endif()
-
 function(CGAL_setup_CGAL_Core_dependencies target)
   if(ARGV1 STREQUAL INTERFACE)
     set(keyword INTERFACE)
   else()
     set(keyword PUBLIC)
   endif()
+
+  # See the release notes of CGAL-4.10: CGAL_Core now requires
+  # Boost.Thread, with all compilers but MSVC.
+  if (NOT MSVC)
+    find_package( Boost 1.48 REQUIRED thread system )
+  endif()
+
   use_CGAL_GMP_support(CGAL_Core ${keyword})
   target_compile_definitions(${target} ${keyword} CGAL_USE_CORE=1)
   target_link_libraries( CGAL_Core ${keyword} CGAL::CGAL ${Boost_LIBRARIES})

Installation/cmake/modules/CGAL_SetupCGAL_ImageIODependencies.cmake

@@ -48,6 +48,7 @@ endif(ZLIB_FOUND)
 set( CGAL_ImageIO_BASENAME CGAL_ImageIO)
 
 set(CGAL_ImageIO_FOUND TRUE)
+set_property(GLOBAL PROPERTY CGAL_ImageIO_FOUND TRUE)
 
 function(CGAL_setup_CGAL_ImageIO_dependencies target)
   if(ARGV1 STREQUAL INTERFACE)

Installation/cmake/modules/CGAL_SetupCGAL_Qt5Dependencies.cmake

@@ -48,6 +48,7 @@ endif()
 #
 if(NOT CGAL_Qt5_MISSING_DEPS)
   set(CGAL_Qt5_FOUND TRUE)
+  set_property(GLOBAL PROPERTY CGAL_Qt5_FOUND TRUE)
 
   include(${CMAKE_CURRENT_LIST_DIR}/CGAL_Qt5_moc_and_resource_files.cmake)
 

Installation/lib/cmake/CGAL/CGALConfig.cmake

@@ -2,20 +2,43 @@
 # This file is the CGALConfig.cmake for a header-only CGAL installation
 #
 
-if(CGALConfig_included)
+# For UseCGAL.cmake
+set( CGAL_REQUESTED_COMPONENTS ${CGAL_FIND_COMPONENTS} )
+
+set(CGAL_LIBRARIES CGAL)
+
+if(CGAL_BUILDING_LIBS)
+  foreach(comp ${CGAL_FIND_COMPONENTS})
+    if(CGAL_${comp}_FOUND)
+      list(APPEND CGAL_LIBRARIES CGAL_${comp})
+    endif()
+  endforeach()
+  return()
+endif()
+
+foreach(comp ${CGAL_FIND_COMPONENTS})
+  if(NOT comp MATCHES "Core|ImageIO|Qt5")
+    message(FATAL_ERROR "The requested CGAL component ${comp} does not exist!")
+  endif()
+  list(APPEND CGAL_LIBRARIES CGAL_${comp})
+endforeach()
+
+set(CGALConfig_all_targets_are_defined TRUE)
+foreach(cgal_lib ${CGAL_LIBRARIES})
+  if(NOT WITH_${cgal_lib})
+    set(CGALConfig_all_targets_are_defined FALSE)
+  endif()
+endforeach()
+if(CGALConfig_all_targets_are_defined)
   return()
 endif()
 
 message(STATUS "Using header-only CGAL")
 
-set(CGALConfig_included TRUE)
-
 get_filename_component(CGAL_CONFIG_DIR "${CMAKE_CURRENT_LIST_FILE}" PATH)
 
 set(CGAL_HEADER_ONLY TRUE)
 
-set( CGAL_REQUESTED_COMPONENTS ${CGAL_FIND_COMPONENTS} )
-
 # Save the current source directory. That variable can be changed by
 # a `CMakeLists.txt`, for `CMakeLists.txt` files that are created in
 # the binary directory.
@@ -76,14 +99,6 @@ list(APPEND CMAKE_MODULE_PATH ${CGAL_MODULES_DIR})
 include( ${CGAL_MODULES_DIR}/CGAL_SCM.cmake )
 CGAL_detect_git(${CGAL_CONFIG_DIR}/../../../..)
 
-set(CGAL_LIBRARIES CGAL)
-foreach(comp ${CGAL_FIND_COMPONENTS})
-  if(NOT comp MATCHES "Core|ImageIO|Qt5")
-    message(FATAL_ERROR "The requested CGAL component ${comp} does not exist!")
-  endif()
-  list(APPEND CGAL_LIBRARIES CGAL_${comp})
-endforeach()
-
 #
 # Search for all dependencies
 #
@@ -91,6 +106,10 @@ foreach(cgal_lib ${CGAL_LIBRARIES})
   include(CGAL_Setup${cgal_lib}Dependencies)
 endforeach()
 
+# this include has to be after the loop that includes the
+# `CGAL_Setup${cgal_lib}Dependencies` files
+include(CGAL_setup_target_dependencies)
+
 #
 # Define the CGAL targets and theirs CGAL:: aliases
 #
@@ -101,21 +120,13 @@ foreach(cgal_lib ${CGAL_LIBRARIES})
     if(NOT TARGET CGAL::${cgal_lib})
       add_library(CGAL::${cgal_lib} ALIAS ${cgal_lib})
     endif()
-  endif()
-endforeach()
-
-# this include has to be after the loop that includes the
-# `CGAL_Setup${cgal_lib}Dependencies` files
-include(CGAL_setup_target_dependencies)
-
-foreach(cgal_lib ${CGAL_LIBRARIES})
-  if(${cgal_lib}_FOUND)
+    if(${cgal_lib} STREQUAL CGAL)
+      target_compile_definitions(CGAL INTERFACE CGAL_HEADER_ONLY=1)
+    endif()
     CGAL_setup_target_dependencies(${cgal_lib} INTERFACE)
   endif()
 endforeach()
 
-target_compile_definitions(CGAL INTERFACE CGAL_HEADER_ONLY=1)
-
 
 #
 #