Support version compatibility checks via find_package command (#4625)

CMake/FlatbuffersConfigVersion.cmake.in

+set(PACKAGE_VERSION "@VERSION_MAJOR@.@VERSION_MINOR@.@VERSION_PATCH@")
+
+# Check whether the requested PACKAGE_FIND_VERSION is compatible
+if("${PACKAGE_VERSION}" VERSION_LESS "${PACKAGE_FIND_VERSION}")
+  set(PACKAGE_VERSION_COMPATIBLE FALSE)
+else()
+  set(PACKAGE_VERSION_COMPATIBLE TRUE)
+  if ("${PACKAGE_VERSION}" VERSION_EQUAL "${PACKAGE_FIND_VERSION}")
+    set(PACKAGE_VERSION_EXACT TRUE)
+  endif()
+endif()

CMake/PackageDebian.cmake

@@ -11,22 +11,6 @@ if (UNIX)
     SET(CPACK_DEBIAN_PACKAGE_HOMEPAGE "https://github.com/google/flatbuffers")
     SET(CPACK_DEBIAN_PACKAGE_MAINTAINER "Vitaly Isaev <vitalyisaev2@gmail.com>")
 
-    # Derive package version from git
-    EXECUTE_PROCESS(
-        COMMAND date +%Y%m%d
-        OUTPUT_VARIABLE DATE
-        OUTPUT_STRIP_TRAILING_WHITESPACE
-    )
-    EXECUTE_PROCESS(
-      COMMAND git describe
-      WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
-      OUTPUT_VARIABLE GIT_DESCRIBE_DIRTY
-      OUTPUT_STRIP_TRAILING_WHITESPACE
-    )
-    string(REGEX REPLACE "^v([0-9]+)\\..*" "\\1" VERSION_MAJOR "${GIT_DESCRIBE_DIRTY}")
-    string(REGEX REPLACE "^v[0-9]+\\.([0-9]+).*" "\\1" VERSION_MINOR "${GIT_DESCRIBE_DIRTY}")
-    string(REGEX REPLACE "^v[0-9]+\\.[0-9]+\\.([0-9]+).*" "\\1" VERSION_PATCH "${GIT_DESCRIBE_DIRTY}")
-    string(REGEX REPLACE "^v[0-9]+\\.[0-9]+\\.[0-9]+\\-([0-9]+).*" "\\1" VERSION_COMMIT "${GIT_DESCRIBE_DIRTY}")
     SET(CPACK_PACKAGE_VERSION_MAJOR ${VERSION_MAJOR})
     SET(CPACK_PACKAGE_VERSION_MINOR ${VERSION_MINOR})
     SET(CPACK_PACKAGE_VERSION_PATCH ${VERSION_PATCH})
@@ -49,7 +33,7 @@ if (UNIX)
     # Package name
     SET(CPACK_DEBIAN_PACKAGE_NAME "flatbuffers")
     SET(CPACK_RESOURCE_FILE_LICENSE ${CMAKE_SOURCE_DIR}/LICENSE.txt)
-    SET(CPACK_PACKAGE_FILE_NAME 
+    SET(CPACK_PACKAGE_FILE_NAME
         "${CPACK_DEBIAN_PACKAGE_NAME}_${CPACK_DEBIAN_PACKAGE_VERSION}_${CPACK_DEBIAN_PACKAGE_ARCHITECTURE}")
 
 endif(UNIX)

CMake/Version.cmake

+find_program(GIT git)
+execute_process(
+    COMMAND ${GIT} describe
+    WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
+    OUTPUT_VARIABLE GIT_DESCRIBE_DIRTY
+    OUTPUT_STRIP_TRAILING_WHITESPACE
+)
+string(REGEX REPLACE "^v([0-9]+)\\..*" "\\1" VERSION_MAJOR "${GIT_DESCRIBE_DIRTY}")
+string(REGEX REPLACE "^v[0-9]+\\.([0-9]+).*" "\\1" VERSION_MINOR "${GIT_DESCRIBE_DIRTY}")
+string(REGEX REPLACE "^v[0-9]+\\.[0-9]+\\.([0-9]+).*" "\\1" VERSION_PATCH "${GIT_DESCRIBE_DIRTY}")
+string(REGEX REPLACE "^v[0-9]+\\.[0-9]+\\.[0-9]+\\-([0-9]+).*" "\\1" VERSION_COMMIT "${GIT_DESCRIBE_DIRTY}")

CMakeLists.txt

@@ -253,6 +253,8 @@ if(FLATBUFFERS_BUILD_GRPCTEST)
   target_link_libraries(grpctest grpc++_unsecure grpc_unsecure gpr pthread dl)
 endif()
 
+include(CMake/Version.cmake)
+
 if(FLATBUFFERS_INSTALL)
   include(GNUInstallDirs)
 
@@ -260,8 +262,9 @@ if(FLATBUFFERS_INSTALL)
 
   set(FB_CMAKE_DIR "${CMAKE_INSTALL_LIBDIR}/cmake/flatbuffers")
 
+  configure_file(CMake/FlatbuffersConfigVersion.cmake.in FlatbuffersConfigVersion.cmake @ONLY)
   install(
-      FILES "CMake/FlatbuffersConfig.cmake"
+      FILES "CMake/FlatbuffersConfig.cmake" "${CMAKE_CURRENT_BINARY_DIR}/FlatbuffersConfigVersion.cmake"
       DESTINATION ${FB_CMAKE_DIR}
   )