Add Protobuf as submodule

This ensures that the user has a working Protobuf installation

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "3rdparty/fmt"]
 	path = 3rdparty/fmt
 	url = https://github.com/fmtlib/fmt.git
+[submodule "3rdparty/protobuf"]
+	path = 3rdparty/protobuf
+	url = https://github.com/google/protobuf.git

CMakeLists.txt

@@ -2,7 +2,6 @@ cmake_minimum_required (VERSION 3.1)
 project(treelite)
 include(cmake/Utils.cmake)
 find_package(OpenMP)
-find_package(Protobuf)
 
 # Use RPATH on Mac OS X as flexible mechanism for locating dependencies
 # See https://blog.kitware.com/upcoming-in-cmake-2-8-12-osx-rpath-support/
@@ -11,11 +10,18 @@ set(CMAKE_MACOSX_RPATH TRUE)
 # Set BUILD_SHARED_LIBS as option. By default, build shared libraries;
 # User can set this to OFF to build static libraries instead.
 option(BUILD_SHARED_LIBS "Build shared library" ON)
-option(DISABLE_PROTOBUF "Disable Protobuf" OFF)
 
 # enable custom logging facility in dmlc-core
 add_definitions(-DDMLC_LOG_CUSTOMIZE)
 
+# Protobuf
+set(protobuf_BUILD_TESTS OFF CACHE BOOL "enable tests for protobuf" FORCE)
+set(protobuf_BUILD_SHARED_LIBS OFF CACHE BOOL "enable shared libs for protobuf" FORCE)
+add_subdirectory(3rdparty/protobuf/cmake)
+set(PROTOBUF_PROTOC_EXECUTABLE protoc)
+set(PROTOBUF_INCLUDE_DIRS "${PROJECT_SOURCE_DIR}/3rdparty/protobuf/src")
+set(PROTOBUF_LIBRARIES libprotobuf)
+
 # check MSVC version
 if(MSVC)
   if(MSVC_VERSION LESS 1900)
@@ -28,10 +34,8 @@ msvc_use_static_runtime()
 
 # OpenMP check
 if(OPENMP_FOUND)
-  message("Got OpenMP")
   add_definitions(-DTREELITE_OPENMP_SUPPORT)
 else(OPENMP_FOUND)
-  message("Don't have OpenMP")
   include(dmlc-core/cmake/Utils.cmake)
   dmlccore_option(USE_OPENMP "Build with OpenMP" OFF)
 endif(OPENMP_FOUND)
@@ -96,15 +100,11 @@ endforeach(g)
 list(REMOVE_ITEM SOURCES ${PROJECT_SOURCE_DIR}/src/cli_main.cc ${COMMON_SOURCES_WITH_PREFIX} ${RUNTIME_SOURCES_WITH_PREFIX})
 
 # Protobuf library
-if (NOT DISABLE_PROTOBUF)
-  if (Protobuf_FOUND OR PROTOBUF_FOUND)
-    set_source_files_properties(src/frontend/protobuf.cc PROPERTIES COMPILE_DEFINITIONS PROTOBUF_SUPPORT)
-    include_directories(${PROTOBUF_INCLUDE_DIRS})
-    include_directories(${CMAKE_CURRENT_BINARY_DIR})
-    protobuf_generate_cpp(PROTO_SRCS PROTO_HDRS src/tree.proto)
-    list(INSERT SOURCES 0 ${PROTO_SRCS} ${PROTO_HDRS})
-  endif()
-endif()
+set_source_files_properties(src/frontend/protobuf.cc PROPERTIES COMPILE_DEFINITIONS PROTOBUF_SUPPORT)
+include_directories(${PROTOBUF_INCLUDE_DIRS})
+include_directories(${CMAKE_CURRENT_BINARY_DIR})
+PROTOBUF_GENERATE_CPP(PROTO_SRCS PROTO_HDRS src/tree.proto)
+list(INSERT SOURCES 0 ${PROTO_SRCS} ${PROTO_HDRS})
 
 # dmlc-core
 set(BUILD_SHARED_LIBS_SAVED "${BUILD_SHARED_LIBS}")  # Save BUILD_SHARED_LIBS
@@ -125,11 +125,7 @@ if (UNIX)
 endif (UNIX)
 
 # Protobuf library
-if (NOT DISABLE_PROTOBUF)
-  if (Protobuf_FOUND OR PROTOBUF_FOUND)
-    list(APPEND LINK_LIBRARIES ${PROTOBUF_LIBRARIES})
-  endif()
-endif()
+list(APPEND LINK_LIBRARIES ${PROTOBUF_LIBRARIES})
 
 add_library(objtreelite OBJECT ${SOURCES})
 add_library(objtreelite_runtime OBJECT ${RUNTIME_SOURCES})

cmake/Utils.cmake

@@ -87,3 +87,70 @@ function(format_gencode_flags flags out)
   endforeach()
   set(${out} "${${out}}" PARENT_SCOPE)
 endfunction(format_gencode_flags flags)
+
+#=============================================================================
+# Copyright 2009 Kitware, Inc.
+# Copyright 2009-2011 Philip Lowman <[email protected]>
+# Copyright 2008 Esben Mose Hansen, Ange Optimization ApS
+#
+# Distributed under the OSI-approved BSD License (the "License");
+# see accompanying file Copyright.txt for details.
+#
+# This software is distributed WITHOUT ANY WARRANTY; without even the
+# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+# See the License for more information.
+#=============================================================================
+# (To distribute this file outside of CMake, substitute the full
+#  License text for the above reference.)
+function(PROTOBUF_GENERATE_CPP SRCS HDRS)
+  if(NOT ARGN)
+    message(SEND_ERROR "Error: PROTOBUF_GENERATE_CPP() called without any proto files")
+    return()
+  endif()
+
+  # Create an include path for each file specified
+  foreach(FIL ${ARGN})
+    get_filename_component(ABS_FIL ${FIL} ABSOLUTE)
+    get_filename_component(ABS_PATH ${ABS_FIL} PATH)
+    list(FIND _protobuf_include_path ${ABS_PATH} _contains_already)
+    if(${_contains_already} EQUAL -1)
+      list(APPEND _protobuf_include_path -I ${ABS_PATH})
+    endif()
+  endforeach()
+
+  if(DEFINED PROTOBUF_IMPORT_DIRS)
+    foreach(DIR ${PROTOBUF_IMPORT_DIRS})
+      get_filename_component(ABS_PATH ${DIR} ABSOLUTE)
+      list(FIND _protobuf_include_path ${ABS_PATH} _contains_already)
+      if(${_contains_already} EQUAL -1)
+        list(APPEND _protobuf_include_path -I ${ABS_PATH})
+      endif()
+    endforeach()
+  endif()
+
+  set(PROTOC_DEPENDENCY ${PROTOBUF_PROTOC_EXECUTABLE})
+
+  set(${SRCS})
+  set(${HDRS})
+  foreach(FIL ${ARGN})
+    get_filename_component(ABS_FIL ${FIL} ABSOLUTE)
+    get_filename_component(FIL_WE ${FIL} NAME_WE)
+
+    list(APPEND ${SRCS} "${CMAKE_CURRENT_BINARY_DIR}/${FIL_WE}.pb.cc")
+    list(APPEND ${HDRS} "${CMAKE_CURRENT_BINARY_DIR}/${FIL_WE}.pb.h")
+
+    add_custom_command(
+      OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/${FIL_WE}.pb.cc"
+           "${CMAKE_CURRENT_BINARY_DIR}/${FIL_WE}.pb.h"
+      COMMAND ${PROTOBUF_PROTOC_EXECUTABLE}
+      ARGS --cpp_out ${CMAKE_CURRENT_BINARY_DIR} ${_protobuf_include_path} ${ABS_FIL}
+      DEPENDS ${ABS_FIL} ${PROTOC_DEPENDENCY}
+      COMMENT "Running C++ protocol buffer compiler on ${FIL}"
+      VERBATIM
+    )
+  endforeach()
+
+  set_source_files_properties(${${SRCS}} ${${HDRS}} PROPERTIES GENERATED TRUE)
+  set(${SRCS} ${${SRCS}} PARENT_SCOPE)
+  set(${HDRS} ${${HDRS}} PARENT_SCOPE)
+endfunction()

docs/install.rst

@@ -164,28 +164,3 @@ to C++ code will be immediately visible to Python side without re-running
   export PYTHONPATH=path/to/treelite/python
   python          # enter interactive session
 
-.. note:: Compiling with Protocol Buffers support
-
-  If your system has Protocol Buffers
-  (`google/protobuf <https://github.com/google/protobuf>`_) library installed,
-  treelite will be compiled with Protocol Buffers support. That is, you will
-  able to read tree ensemble models that had been serialized using Protocol
-  Buffers. Protocol Buffers support is strictly optional; treelite can be
-  compiled without it. Should you decide to use Protocol Buffers, you should
-  specify your ensemble model according to the specification `src/tree.proto
-  <https://github.com/dmlc/treelite/blob/master/src/tree.proto>`_.
-
-  **Binary releases hosted on PyPI have been compiled with Protocol Buffers support.**
-
-  **On Windows,** you should specify the root directory containing Protobuf
-  compilers and libraries by setting the environment variable
-  ``CMAKE_PREFIX_PATH`` as follows:
-
-  .. code-block:: dosbatch
-
-    mkdir build
-    cd build
-
-    :: Specify location of protobuf (Protocol Buffers)
-    set CMAKE_PREFIX_PATH=C:\path\to\protobuf
-    cmake .. -G"Visual Studio 15 2017 Win64"