CMake: set FLTK_VERSION and FLTK_FLUID_EXECUTABLE in the cache

This is useful if FLTK is built as a subproject, for instance by
using FetchContent.

CMakeLists.txt

@@ -57,6 +57,11 @@ if(0)
   fl_debug_var(CMAKE_VERSION)
 endif()
 
+# Set FLTK_VERSION in the cache so user projects can access it,
+# for instance if FLTK is built as a subproject (FetchContent)
+
+set(FLTK_VERSION ${FLTK_VERSION} CACHE STRING "FLTK version" FORCE)
+
 #######################################################################
 # basic setup
 #######################################################################
@@ -115,13 +120,22 @@ endif()
 add_subdirectory(src)
 
 #######################################################################
-# build fluid
+# build fluid (optional)
 #######################################################################
 
+set(FLTK_FLUID_EXECUTABLE "")
+
 if(FLTK_BUILD_FLUID)
   add_subdirectory(fluid)
 endif(FLTK_BUILD_FLUID)
 
+# Set FLTK_FLUID_EXECUTABLE in the cache for user projects.
+# This can be used if FLTK has been built as a subproject.
+
+set(FLTK_FLUID_EXECUTABLE
+    "${FLTK_FLUID_EXECUTABLE}" CACHE STRING
+    "FLTK's 'fluid' executable")
+
 #######################################################################
 # build fltk-options
 #######################################################################

fluid/CMakeLists.txt

@@ -177,8 +177,13 @@ if(WIN32)
   list(APPEND TARGETS fluid-cmd)
   add_executable(fluid-cmd fluid.cxx)
   target_link_libraries(fluid-cmd PRIVATE fluid-lib)
+  set(FLTK_FLUID_EXECUTABLE fltk::fluid-cmd)
+else()
+  set(FLTK_FLUID_EXECUTABLE fltk::fluid)
 endif()
 
+set(FLTK_FLUID_EXECUTABLE "${FLTK_FLUID_EXECUTABLE}" PARENT_SCOPE)
+
 # Create aliases for all targets
 
 foreach(tgt ${TARGETS})