fix up Cmake/protobuf disaster (valhalla#4207)

* use protobuf's CMake config instead of CMake's own

* add todo

* ugly workaround

* manually find & link abseil to protobuf

* changelog

* comment out the dll line

* boil down to linking only the used abseil library

CHANGELOG.md

@@ -5,6 +5,7 @@
    * FIXED: when reclassifying ferry edges, remove destonly from ways only if the connecting way was destonly [#4118](https://github.com/valhalla/valhalla/pull/4118)
    * FIXED: typo in use value of map matching API (`platform_connection` was misspelled) [#4174](https://github.com/valhalla/valhalla/pull/4174)
    * FIXED: fix crash in timedistancebssmatrix.cc  [#4244](https://github.com/valhalla/valhalla/pull/4244)
+   * FIXED: missing protobuf CMake configuration to link abseil for protobuf >= 3.22.0 [#4207](https://github.com/valhalla/valhalla/pull/4207)
 * **Enhancement**
    * UPDATED: French translations, thanks to @xlqian [#4159](https://github.com/valhalla/valhalla/pull/4159)
    * CHANGED: -j flag for multithreaded executables to override mjolnir.concurrency [#4168](https://github.com/valhalla/valhalla/pull/4168)

CMakeLists.txt

@@ -181,6 +181,34 @@ endif()
 
 if(NOT Protobuf_FOUND)
   find_package(Protobuf REQUIRED)
+
+  # orchestrated effort of both protobuf & cmake are responsible for the next lines..
+
+  # TODO: monitor how protobuf Linux packages evolve. Eventually everyone should use
+  # the Apple configuration, but e.g. apt does not install CMake config with protobuf
+  if(Protobuf_VERSION VERSION_GREATER_EQUAL 4.22.0)
+    # this might be needed for some Apple/Linux protobuf versions
+    # add_definitions(-DPROTOBUF_USE_DLLS)
+    if(APPLE OR WIN32)
+      # CONFIG mode is ideal for new abseil protobuf builds, which uses the protobuf-provided
+      # CMake configuration instead of CMake internal one, as that's not looking for abseil:
+      # https://github.com/valhalla/valhalla/issues/4173#issuecomment-1638067950
+      # Newer protobuf versions require a protobuf_MODULE_COMPATIBLE to be able 
+      # to see the protobuf_generate_cpp() CMake function
+      set(protobuf_MODULE_COMPATIBLE ON CACHE BOOL "")
+      find_package(Protobuf REQUIRED CONFIG)
+    else()
+      # linux might not have CMake config installed (e.g. Debian derivatives)
+      # need to link protobuf to abseil manually
+      find_package(Protobuf REQUIRED)
+      find_package(absl REQUIRED)
+      if(TARGET protobuf::libprotobuf-lite)
+        target_link_libraries(protobuf::libprotobuf-lite INTERFACE "absl::absl_log")
+      elseif(TARGET protobuf::libprotobuf)
+        target_link_libraries(protobuf::libprotobuf INTERFACE "absl::absl_log")
+      endif()
+    endif()
+  endif()
 endif()
 
 message(STATUS "Using pbf headers from ${PROTOBUF_INCLUDE_DIR}")

proto/CMakeLists.txt

@@ -20,6 +20,7 @@ if(ENABLE_DATA_TOOLS)
     ${VALHALLA_SOURCE_DIR}/third_party/OSM-binary/src/osmformat.proto)
 endif()
 
+# TODO: this seems to be deprecated, see https://github.com/valhalla/valhalla/pull/4207
 protobuf_generate_cpp(protobuf_srcs protobuf_hdrs ${protobuf_descriptors})
 
 valhalla_module(NAME proto