feat cmake: add download_userver()

CMakeLists.txt

@@ -1,21 +1,18 @@
 cmake_minimum_required(VERSION 3.12)
 project(service_template CXX)
 
+list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR})
+include(DownloadUserver)
 
 # Adding userver dependency
 find_package(userver COMPONENTS core postgresql QUIET)
 if(NOT userver_FOUND)  # Fallback to subdirectory usage
-    # Compatibility mode: some systems don't support these features
-    set(USERVER_FEATURE_CRYPTOPP_BLAKE2 OFF CACHE BOOL "" FORCE)
-    set(USERVER_FEATURE_GRPC_CHANNELZ OFF CACHE BOOL "" FORCE)
-    set(USERVER_FEATURE_REDIS_HI_MALLOC ON CACHE BOOL "" FORCE)
-
-    if (EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/third_party/userver)
-        message(STATUS "Using userver framework from third_party/userver")
-        add_subdirectory(third_party/userver)
-    else()
-        message(FATAL_ERROR "Either install the userver or provide a path to it")
-    endif()
+    download_userver(
+      # Compatibility mode: some systems don't support these features
+      FEATURES_OFF
+        CRYPTOPP_BLAKE2
+	GRPC_CHANNELZ
+    )
 endif()
 
 userver_setup_environment()

DownloadUserver.cmake

@@ -0,0 +1,28 @@
+include(FetchContent)
+
+function(download_userver)
+  set(OPTIONS)
+  set(ONE_VALUE_ARGS VERSION)
+  set(MULTI_VALUE_ARGS FEATURES FEATURES_OFF)
+  cmake_parse_arguments(
+      ARG "${OPTIONS}" "${ONE_VALUE_ARGS}" "${MULTI_VALUE_ARGS}" ${ARGN}
+  )
+  if(NOT ARG_VERSION)
+    set(ARG_VERSION develop)
+  endif()
+
+  set(FETCHCONTENT_QUIET OFF CACHE BOOL "" FORCE)
+  FetchContent_Declare(
+    userver
+    GIT_REPOSITORY https://github.com/userver-framework/userver.git
+    GIT_TAG ${ARG_VERSION}
+  )
+  FetchContent_MakeAvailable(userver)
+
+  foreach(FEATURE ${ARG_FEATURES})
+    set(USERVER_FEATURE_${FEATURE} ON CACHE BOOL "" FORCE)
+  endforeach()
+  foreach(FEATURE ${ARG_FEATURES_OFF})
+    set(USERVER_FEATURE_${FEATURE} OFF CACHE BOOL "" FORCE)
+  endforeach()
+endfunction()