Fix the problem that protobuf cannot be used as a DEPS argument in cc_library.

cmake/external/protobuf.cmake

@@ -14,11 +14,41 @@
 
 INCLUDE(ExternalProject)
 
+# Print and set the protobuf library information,
+# finish this cmake process and exit from this file.
 macro(PROMPT_PROTOBUF_LIB)
+    SET(protobuf_DEPS ${ARGN})
+
     MESSAGE(STATUS "Protobuf protoc executable: ${PROTOBUF_PROTOC_EXECUTABLE}")
     MESSAGE(STATUS "Protobuf library: ${PROTOBUF_LIBRARY}")
     MESSAGE(STATUS "Protobuf version: ${PROTOBUF_VERSION}")
     INCLUDE_DIRECTORIES(${PROTOBUF_INCLUDE_DIR})
+
+    # Assuming that all the protobuf libraries are of the same type.
+    IF(${PROTOBUF_LIBRARY} MATCHES "${STATIC_LIBRARY_SUFFIX}$")
+        SET(protobuf_LIBTYPE STATIC)
+    ELSEIF(${PROTOBUF_LIBRARY} MATCHES "${DYNAMIC_LIBRARY_SUFFIX}$")
+        SET(protobuf_LIBTYPE SHARED)
+    ELSE()
+        MESSAGE(FATAL_ERROR "Unknown library type: ${PROTOBUF_LIBRARY}")
+    ENDIF()
+
+    ADD_LIBRARY(protobuf ${protobuf_LIBTYPE} IMPORTED GLOBAL)
+    SET_PROPERTY(TARGET protobuf PROPERTY IMPORTED_LOCATION ${PROTOBUF_LIBRARY})
+
+    ADD_LIBRARY(protobuf_lite ${protobuf_LIBTYPE} IMPORTED GLOBAL)
+    SET_PROPERTY(TARGET protobuf_lite PROPERTY IMPORTED_LOCATION ${PROTOBUF_LITE_LIBRARY})
+
+    ADD_LIBRARY(protoc ${protobuf_LIBTYPE} IMPORTED GLOBAL)
+    SET_PROPERTY(TARGET protoc PROPERTY IMPORTED_LOCATION ${PROTOC_LIBRARY})
+
+    FOREACH(dep ${protobuf_DEPS})
+        ADD_DEPENDENCIES(protobuf ${dep})
+        ADD_DEPENDENCIES(protobuf_lite ${dep})
+        ADD_DEPENDENCIES(protoc ${dep})
+    ENDFOREACH()
+
+    LIST(APPEND external_project_dependencies protobuf)
     RETURN()
 endmacro()
 macro(SET_PROTOBUF_VERSION)
@@ -43,8 +73,9 @@ if (NOT "${PROTOBUF_ROOT}" STREQUAL "")
 endif()
 
 FUNCTION(build_protobuf TARGET_NAME BUILD_FOR_HOST)
-    SET(PROTOBUF_SOURCES_DIR ${THIRD_PARTY_PATH}/${TARGET_NAME})
-    SET(PROTOBUF_INSTALL_DIR ${THIRD_PARTY_PATH}/install/${TARGET_NAME})
+    STRING(REPLACE "extern_" "" TARGET_DIR_NAME "${TARGET_NAME}")
+    SET(PROTOBUF_SOURCES_DIR ${THIRD_PARTY_PATH}/${TARGET_DIR_NAME})
+    SET(PROTOBUF_INSTALL_DIR ${THIRD_PARTY_PATH}/install/${TARGET_DIR_NAME})
 
     SET(${TARGET_NAME}_INCLUDE_DIR "${PROTOBUF_INSTALL_DIR}/include" PARENT_SCOPE)
     SET(PROTOBUF_INCLUDE_DIR "${PROTOBUF_INSTALL_DIR}/include" PARENT_SCOPE)
@@ -109,6 +140,8 @@ IF(NOT CMAKE_CROSSCOMPILING)
         SET_PROTOBUF_VERSION()
         IF("${PROTOBUF_VERSION}" VERSION_LESS "3.1.0")
             SET(PROTOBUF_FOUND OFF)
+        ELSE()
+            PROMPT_PROTOBUF_LIB()
         ENDIF()
     ENDIF(PROTOBUF_FOUND)
 ELSE()
@@ -120,18 +153,22 @@ ELSE()
 ENDIF()
 
 IF(NOT PROTOBUF_FOUND)
-    build_protobuf(protobuf FALSE)
-    LIST(APPEND external_project_dependencies protobuf)
+    build_protobuf(extern_protobuf FALSE)
 
-    SET(PROTOBUF_INCLUDE_DIR ${protobuf_INCLUDE_DIR}
+    SET(PROTOBUF_INCLUDE_DIR ${extern_protobuf_INCLUDE_DIR}
         CACHE PATH "protobuf include directory." FORCE)
-    IF(NOT CMAKE_CROSSCOMPILING)
-        SET(PROTOBUF_PROTOC_EXECUTABLE ${protobuf_PROTOC_EXECUTABLE}
+    SET(PROTOBUF_LITE_LIBRARY ${extern_protobuf_LITE_LIBRARY}
+        CACHE FILEPATH "protobuf lite library." FORCE)
+    SET(PROTOBUF_LIBRARY ${extern_protobuf_LIBRARY}
+        CACHE FILEPATH "protobuf library." FORCE)
+    SET(PROTOBUF_PROTOC_LIBRARY ${extern_protobuf_PROTOC_LIBRARY}
+        CACHE FILEPATH "protoc library." FORCE)
+
+    IF(CMAKE_CROSSCOMPILING)
+        PROMPT_PROTOBUF_LIB(protobuf_host extern_protobuf)
+    ELSE()
+        SET(PROTOBUF_PROTOC_EXECUTABLE ${extern_protobuf_PROTOC_EXECUTABLE}
             CACHE FILEPATH "protobuf executable." FORCE)
+        PROMPT_PROTOBUF_LIB(extern_protobuf)
     ENDIF()
-    SET(PROTOBUF_LITE_LIBRARY ${protobuf_LITE_LIBRARY} CACHE FILEPATH "protobuf lite library." FORCE)
-    SET(PROTOBUF_LIBRARY ${protobuf_LIBRARY} CACHE FILEPATH "protobuf library." FORCE)
-    SET(PROTOBUF_PROTOC_LIBRARY ${protobuf_PROTOC_LIBRARY} CACHE FILEPATH "protoc library." FORCE)
 ENDIF(NOT PROTOBUF_FOUND)
-
-PROMPT_PROTOBUF_LIB()
\ No newline at end of file