[cmake] Change Build_Deps option to take either Never/Always/IfNotFound, cleaning

- Use Global Properties to check if a package has been found.
  This information should not go in the cmake cache

deps/CMakeLists.txt

@@ -29,11 +29,19 @@ include(external_dependency.cmake)
 #                     will not be included in the ALL target of the project.
 #                     In particular the dependency will not be installed.
 
-option(Build_Deps "Build dependencies from source" OFF)
+if(NOT DEFINED Build_Deps)
+  set(Build_Deps "Never" CACHE STRING "Do we build dependencies from source? [Never/Always/IfNotFound]")
+else()
+  set(Build_Deps_Opts "Never" "Always" "IfNotFound")
+  if(NOT ${Build_Deps} IN_LIST Build_Deps_Opts)
+    message(FATAL_ERROR "Build_Deps option should be either 'Never', 'Always' or 'IfNotFound'")
+  endif()
+  set(Build_Deps ${Build_Deps} CACHE STRING "Do we build dependencies from source? [Never/Always/IfNotFound]")
+endif()
 
 # -- GTest --
 external_dependency(GTest
-  GIT_REPO github:google/googletest
+  GIT_REPO https://github.com/google/googletest
   TAG release-1.10.0
   EXCLUDE_FROM_ALL
 )

deps/external_dependency.cmake

@@ -2,37 +2,46 @@
 function(external_dependency)
   cmake_parse_arguments(ARG "EXCLUDE_FROM_ALL" "VERSION;GIT_REPO;TAG" "" ${ARGN})
 
-  # Was dependency already found?
+  # -- Was dependency already found?
+  get_property(${ARGV0}_FOUND GLOBAL PROPERTY ${ARGV0}_FOUND)
   if(${ARGV0}_FOUND)
-    message(STATUS "Dependency ${ARGV0} was already resolved")
+    message(STATUS "Dependency ${ARGV0} was already resolved.")
-  else()
+    return()
-    if(NOT Build_Deps)
+  endif()
-      find_package(${ARGV0} ${${ARGV0}_VERSION} QUIET)
+
-    endif()
+  # -- Try to find package in system.
+  if(NOT Build_Deps STREQUAL "Always")
+    find_package(${ARGV0} ${${ARGV0}_VERSION} QUIET)
     if(${ARGV0}_FOUND)
-      message(STATUS "Found dependency ${ARGV0} with find_package command")
+      message(STATUS "Found dependency ${ARGV0} in system.")
-    else()
+      return()
-      message(STATUS " =============== Configuring Dependency ${ARGV0} =============== ")
+    elseif(Build_Deps STREQUAL "Never")
-      if(ARG_EXCLUDE_FROM_ALL)
+      message(FATAL_ERROR "Could not find dependency ${ARGV0} in system.")
-        set(subdir_opts EXCLUDE_FROM_ALL)
-      endif()
-      if(IS_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/${ARGV0})
-        message(STATUS "Found sources for dependency ${ARGV0} at ${CMAKE_CURRENT_SOURCE_DIR}/${ARGV0}.")
-        add_subdirectory(${ARGV0} ${subdir_opts})
-      elseif(ARG_GIT_REPO)
-        set(bin_dir ${CMAKE_CURRENT_BINARY_DIR}/${ARGV0})
-        set(src_dir ${bin_dir}_src)
-        if(NOT IS_DIRECTORY ${src_dir})
-          if(ARG_TAG)
-            set(clone_opts --branch ${ARG_TAG} -c advice.detachedHead=false)
-          endif()
-          execute_process(COMMAND git clone ${ARG_GIT_REPO} --depth 1 ${clone_opts} ${src_dir})
-        endif()
-        add_subdirectory(${src_dir} ${bin_dir} ${subdir_opts})
-      else()
-        message(FATAL_ERROR "Could not find dependency ${ARGV0}")
-      endif()
-      set(${ARGV0}_FOUND TRUE PARENT_SCOPE)
     endif()
   endif()
+
+  # -- Build package from source
+  message(STATUS " =============== Configuring Dependency ${ARGV0} =============== ")
+  if(ARG_EXCLUDE_FROM_ALL)
+    set(subdir_opts EXCLUDE_FROM_ALL)
+  endif()
+  if(IS_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/${ARGV0})
+    message(STATUS "Found sources for dependency ${ARGV0} at ${CMAKE_CURRENT_SOURCE_DIR}/${ARGV0}.")
+    add_subdirectory(${ARGV0} ${subdir_opts})
+  elseif(ARG_GIT_REPO)
+    set(bin_dir ${CMAKE_CURRENT_BINARY_DIR}/${ARGV0})
+    set(src_dir ${bin_dir}_src)
+    if(NOT IS_DIRECTORY ${src_dir})
+      if(ARG_TAG)
+        set(clone_opts --branch ${ARG_TAG} -c advice.detachedHead=false)
+      endif()
+      execute_process(COMMAND git clone ${ARG_GIT_REPO} --depth 1 ${clone_opts} ${src_dir})
+    endif()
+    add_subdirectory(${src_dir} ${bin_dir} ${subdir_opts})
+  else()
+    message(FATAL_ERROR "Could not find or build dependency ${ARGV0}.")
+  endif()
+
+  set_property(GLOBAL PROPERTY ${ARGV0}_FOUND TRUE)
+
 endfunction()