feature: provide protobuf as a fallback dependency (#96)

If the protobuf library does not exist on the system, the library is
fetched and installed from github. This provides greater compatibility
for various operating systems.

.gitmodules

@@ -1,9 +1,6 @@
 [submodule "third_party/yaml-cpp"]
 	path = third_party/yaml-cpp
 	url = https://github.com/jbeder/yaml-cpp.git
-[submodule "third_party/googletest"]
-	path = third_party/googletest
-	url = https://github.com/google/googletest.git
 [submodule "third_party/substrait"]
 	path = third_party/substrait
 	url = https://github.com/substrait-io/substrait.git

CMakeLists.txt

@@ -1,6 +1,6 @@
 # SPDX-License-Identifier: Apache-2.0
 
-cmake_minimum_required(VERSION 3.20)
+cmake_minimum_required(VERSION 3.24)
 
 # set the project name
 project(substrait-cpp)
@@ -39,11 +39,19 @@ include_directories(src)
 # available otherwise we fallback to the older protobuf method.
 find_package(Protobuf QUIET CONFIG)
 if(${Protobuf_FOUND})
+  message(STATUS "Modern protobuf library located.")
   set(ABSL_INCLUDED_WITH_PROTOBUF ON)
 else()
-  find_package(Protobuf REQUIRED)
-  include_directories(${Protobuf_INCLUDE_DIRS})
-  set(ABSL_INCLUDED_WITH_PROTOBUF OFF)
+  find_package(Protobuf QUIET)
+  if(${Protobuf_FOUND})
+    message(STATUS "Legacy protobuf library located.")
+    include_directories(${Protobuf_INCLUDE_DIRS})
+    set(ABSL_INCLUDED_WITH_PROTOBUF OFF)
+  else()
+    message(STATUS "Fetching external protobuf library.")
+    include(third_party/protobuf.cmake)
+    set(ABSL_INCLUDED_WITH_PROTOBUF ON)
+  endif()
 endif()
 
 add_subdirectory(third_party)

export/planloader/CMakeLists.txt

@@ -1,9 +1,9 @@
 # SPDX-License-Identifier: Apache-2.0
 
-if(NOT BUILD_SUBDIR_NAME EQUAL "release")
+if(CMAKE_BUILD_TYPE MATCHES Debug)
   message(
-    SEND_ERROR,
-    "The planloader library does not work in Debug mode due to its dependencies."
+    WARNING
+      "The planloader library does not work well in Debug mode due to bundled heap checking."
   )
 endif()
 

src/substrait/proto/CMakeLists.txt

@@ -65,8 +65,10 @@ foreach(PROTO_FILE IN LISTS PROTOBUF_FILELIST)
   set(PROTO_SRC ${PROTO_OUTPUT_PARENT_DIR}/proto/${RELATIVE_PROTO_PATH}.pb.cc)
   add_custom_command(
     OUTPUT ${PROTO_SRC} ${PROTO_HDR}
-    COMMAND protobuf::protoc "--proto_path=${GENERATED_PROTO_TOPLEVEL_DIR}"
-            "--cpp_out=${PROTO_OUTPUT_MIDLEVEL_DIR}" ${GENERATED_PROTO_FILE}
+    COMMAND
+      protobuf::protoc
+      "--proto_path=${GENERATED_PROTO_TOPLEVEL_DIR}:${protobuf_SOURCE_DIR}/src"
+      "--cpp_out=${PROTO_OUTPUT_MIDLEVEL_DIR}" ${GENERATED_PROTO_FILE}
     DEPENDS ${GENERATED_PROTOBUF_LIST} protobuf::protoc
     COMMENT "Generated C++ protobuf module for ${PROTO_FILE}"
     VERBATIM)

third_party/CMakeLists.txt

@@ -8,9 +8,23 @@ endif()
 include(datetime.cmake)
 
 add_subdirectory(fmt)
-add_subdirectory(googletest)
 
+find_package(GTest QUIET)
+if(NOT ${GTEST_FOUND})
+  message(STATUS "Retrieving external GoogleTest library.")
+  include(FetchContent)
+  fetchcontent_declare(
+    GTest
+    GIT_REPOSITORY https://github.com/google/googletest.git
+    GIT_TAG v1.14.0
+    OVERRIDE_FIND_PACKAGE)
+  fetchcontent_makeavailable(GTest)
+endif()
+
+set(PREVIOUS_BUILD_TESTING ${BUILD_TESTING})
+set(BUILD_TESTING OFF)
 add_subdirectory(protobuf-matchers)
+set(BUILD_TESTING ${PREVIOUS_BUILD_TESTING})
 
 set(YAML_CPP_BUILD_TESTS
     OFF

third_party/protobuf.cmake

@@ -0,0 +1,19 @@
+# SPDX-License-Identifier: Apache-2.0
+
+include_guard(GLOBAL)
+
+set(ABSL_PROPAGATE_CXX_STD ON)
+
+include(FetchContent)
+FetchContent_Declare(GTest
+        GIT_REPOSITORY https://github.com/google/googletest.git
+        GIT_TAG v1.14.0
+        OVERRIDE_FIND_PACKAGE
+)
+FetchContent_Declare(Protobuf
+        GIT_REPOSITORY https://github.com/protocolbuffers/protobuf.git
+        GIT_TAG v23.4
+        OVERRIDE_FIND_PACKAGE
+)
+set(protobuf_BUILD_TESTS OFF CACHE INTERNAL "")
+FetchContent_MakeAvailable(Protobuf GTest)