Add RPM packaging support (#5177)

* Add RPM packaging support

Using the existing PackageDebian as template add support for
generating an rpm with the package target.

* Restore debian package target

Also add an option to advertise the fact.

* Update package description

C-n-p from README.md

* Update rpm package maintainer

CMake/DESCRIPTION.txt

+FlatBuffers is a cross platform serialization library architected for
+maximum memory efficiency. It allows you to directly access serialized
+data without parsing/unpacking it first, while still having great 
+forwards/backwards compatibility.

CMake/PackageDebian.cmake

@@ -37,5 +37,3 @@ if (UNIX)
         "${CPACK_DEBIAN_PACKAGE_NAME}_${CPACK_DEBIAN_PACKAGE_VERSION}_${CPACK_DEBIAN_PACKAGE_ARCHITECTURE}")
 
 endif(UNIX)
-
-INCLUDE(CPack)

CMake/PackageRedhat.cmake

+if (UNIX)
+    set(CPACK_GENERATOR "RPM")
+    set(CPACK_SOURCE_TGZ "ON")
+
+    set(CPACK_PACKAGE_DESCRIPTION_SUMMARY "FlatBuffers serialization library and schema compiler.")
+    
+    set(CPACK_RPM_PACKAGE_HOMEPAGE "https://github.com/google/flatbuffers")
+    set(CPACK_RPM_PACKAGE_MAINTAINER "Marc Butler <mockbutler@gmail.com>")
+
+    set(CPACK_PACKAGE_VERSION_MAJOR ${VERSION_MAJOR})
+    set(CPACK_PACKAGE_VERSION_MINOR ${VERSION_MINOR})
+    set(CPACK_PACKAGE_VERSION_PATCH ${VERSION_PATCH})
+    set(CPACK_PACKAGE_VERSION "${VERSION_MAJOR}.${VERSION_MINOR}.${VERSION_PATCH}-${VERSION_COMMIT}")
+    set(CPACK_RPM_PACKAGE_VERSION "${CPACK_PACKAGE_VERSION}")
+
+    set(CPACK_RPM_PACKAGE_NAME "flatbuffers")
+
+    # Assume this is not a cross complation build.
+    if(NOT CPACK_RPM_PACKAGE_ARCHITECTURE)
+        set(CPACK_RPM_PACKAGE_ARCHITECTURE "${CMAKE_SYSTEM_PROCESSOR}")
+    endif(NOT CPACK_RPM_PACKAGE_ARCHITECTURE)
+
+    set(CPACK_RPM_PACKAGE_VENDOR "Google, Inc.")
+    set(CPACK_RPM_PACKAGE_LICENSE "Apache 2.0")
+    set(CPACK_RESOURCE_FILE_LICENSE ${CMAKE_SOURCE_DIR}/LICENSE.txt)
+    set(CPACK_PACKAGE_DESCRIPTION_FILE ${CMAKE_SOURCE_DIR}/CMake/DESCRIPTION.txt)
+
+    # This may reduce rpm compatiblity with very old systems.
+    set(CPACK_RPM_COMPRESSION_TYPE lzma)
+    
+    set(CPACK_RPM_PACKAGE_NAME "flatbuffers")
+    set(CPACK_PACKAGE_FILE_NAME
+        "${CPACK_RPM_PACKAGE_NAME}_${CPACK_RPM_PACKAGE_VERSION}_${CPACK_RPM_PACKAGE_ARCHITECTURE}")
+endif(UNIX)

CMakeLists.txt

@@ -23,7 +23,13 @@ option(FLATBUFFERS_LIBCXX_WITH_CLANG "Force libc++ when using Clang" ON)
 option(FLATBUFFERS_CODE_SANITIZE
       "Add '-fsanitize' flags to 'flattests' and 'flatc' targets."
       OFF)
-
+option(FLATBUFFERS_PACKAGE_REDHAT
+       "Build an rpm using the 'package' target."
+       OFF)
+option(FLATBUFFERS_PACKAGE_DEBIAN
+       "Build an deb using the 'package' target."
+       OFF)
+  
 if(NOT FLATBUFFERS_BUILD_FLATC AND FLATBUFFERS_BUILD_TESTS)
     message(WARNING
     "Cannot build tests without building the compiler. Tests will be disabled.")
@@ -443,6 +449,13 @@ endif()
 
 include(CMake/BuildFlatBuffers.cmake)
 
-if(FLATBUFFERS_PACKAGE_DEBIAN)
-    include(CMake/PackageDebian.cmake)
+if(UNIX)
+    # Use of CPack only supported on Linux systems.
+    if(FLATBUFFERS_PACKAGE_DEBIAN)
+        include(CMake/PackageDebian.cmake)
+    endif()
+    if (FLATBUFFERS_PACKAGE_REDHAT)
+        include(CMake/PackageRedhat.cmake)
+    endif()
+    include(CPack)
 endif()