Merge branch 'unstable' into 3.0.x

Author: Wentzell

deps/external_dependency.cmake

@@ -72,9 +72,18 @@ function(external_dependency)
     set(src_dir ${bin_dir}_src)
     if(NOT IS_DIRECTORY ${src_dir})
       if(ARG_GIT_TAG)
-	set(clone_opts --branch ${ARG_GIT_TAG} -c advice.detachedHead=false)
+        set(clone_opts --branch ${ARG_GIT_TAG} -c advice.detachedHead=false)
+      endif()
+      if(NOT GIT_EXECUTABLE)
+        find_package(Git REQUIRED)
+      endif()
+      execute_process(COMMAND ${GIT_EXECUTABLE} clone ${ARG_GIT_REPO} --depth 1 ${clone_opts} ${src_dir}
+        RESULT_VARIABLE clone_failed
+        ERROR_VARIABLE clone_error
+      )
+      if(clone_failed)
+        message(FATAL_ERROR "Failed to clone sources for dependency ${ARGV0}.\n ${clone_error}")
       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()