improve handling of third-party dependencies in CMake

CMakeLists.txt

@@ -15,17 +15,21 @@ option(BLOATY_ENABLE_CMAKETARGETS "Enable installing cmake target files." ON)
 option(BLOATY_ENABLE_BUILDID "Enable build id." ON)
 option(BLOATY_ENABLE_RE2 "Enable the support for regular expression functions." ON)
 option(BLOATY_PREFER_SYSTEM_CAPSTONE "Prefer to use the system capstone if available" YES)
+option(BLOATY_PREFER_SYSTEM_PROTOBUF "Prefer to use the system protobuf if available" YES)
+option(BLOATY_PREFER_SYSTEM_RE2 "Prefer to use the system re2 if available" YES)
 
 if(UNIX OR MINGW)
 find_package(PkgConfig)
 find_package(ZLIB)
-if(BLOATY_ENABLE_RE2)
+if(BLOATY_ENABLE_RE2 AND BLOATY_PREFER_SYSTEM_RE2)
   pkg_search_module(RE2 re2)
 endif()
 if(BLOATY_PREFER_SYSTEM_CAPSTONE)
   pkg_search_module(CAPSTONE capstone)
 endif()
-pkg_search_module(PROTOBUF protobuf)
+if(BLOATY_PREFER_SYSTEM_PROTOBUF)
+  pkg_search_module(PROTOBUF protobuf)
+endif()
 if(BLOATY_ENABLE_RE2)
   if(RE2_FOUND)
     MESSAGE(STATUS "System re2 found, using")
@@ -65,11 +69,13 @@ if(NOT CMAKE_BUILD_TYPE)
       FORCE)
 endif()
 
-# Check out Git submodules.
-if (EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/.gitmodules")
-  execute_process (COMMAND git submodule update --init --recursive
-                   WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
-endif()
+# Helper function for checking out Git submodules.
+function(init_submodule PATH)
+  execute_process(
+    COMMAND git submodule update --init --recursive "${PATH}"
+    WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
+  )
+endfunction()
 
 # Add third_party libraries, disabling as much as we can of their builds.
 
@@ -105,6 +111,7 @@ if(UNIX OR MINGW)
     if(RE2_FOUND)
       include_directories(${RE2_INCLUDE_DIRS})
     else()
+      init_submodule(third_party/re2)
       set(RE2_BUILD_TESTING OFF CACHE BOOL "enable testing for RE2" FORCE)
       add_subdirectory(third_party/re2)
       include_directories(third_party/re2)
@@ -113,6 +120,7 @@ if(UNIX OR MINGW)
   if(CAPSTONE_FOUND)
     include_directories(${CAPSTONE_INCLUDE_DIRS})
   else()
+    init_submodule(third_party/capstone)
     set(CAPSTONE_BUILD_SHARED OFF CACHE BOOL "Build shared library" FORCE)
     set(CAPSTONE_BUILD_TESTS OFF CACHE BOOL "Build tests" FORCE)
     add_subdirectory(third_party/capstone)
@@ -121,17 +129,20 @@ if(UNIX OR MINGW)
   if(PROTOBUF_FOUND)
     include_directories(${PROTOBUF_INCLUDE_DIRS})
   else()
+    init_submodule(third_party/protobuf)
     set(protobuf_BUILD_TESTS OFF CACHE BOOL "enable tests for proto2" FORCE)
     set(protobuf_BUILD_SHARED_LIBS OFF CACHE BOOL "enable shared libs for proto2" FORCE)
     add_subdirectory(third_party/protobuf/cmake)
     include_directories(SYSTEM third_party/protobuf/src)
   endif()
   if(NOT ZLIB_FOUND)
+    init_submodule(third_party/zlib)
     add_subdirectory(third_party/zlib)
     include_directories(SYSTEM third_party/zlib)
   endif()
 else()
   if(BLOATY_ENABLE_RE2)
+    init_submodule(third_party/re2)
     set(RE2_BUILD_TESTING OFF CACHE BOOL "enable testing for RE2" FORCE)
     add_subdirectory(third_party/re2)
     include_directories(third_party/re2)
@@ -165,6 +176,7 @@ endif()
 include_directories(.)
 include_directories(src)
 if(NOT absl_FOUND)
+  init_submodule(third_party/abseil-cpp)
   include_directories(third_party/abseil-cpp)
 endif()
 include_directories("${CMAKE_CURRENT_BINARY_DIR}/src")
@@ -366,6 +378,7 @@ else()
 
     if(BUILD_TESTING)
       option(INSTALL_GTEST "" OFF)
+      init_submodule(third_party/googletest)
       add_subdirectory(third_party/googletest)
       include_directories(third_party/googletest/googletest/include)
       include_directories(third_party/googletest/googlemock/include)