Added build_flatbuffers function to CMake.

This function is designed to be called by projects that use FlatBuffers.
It takes a list of FlatBuffers schemas and a list of schema include
directories, and generates build rules to create generated headers
and/or binary schemas for those files, as well as optionally copying
all of the text schemas into a directory for your use (for example if
you need to parse text schemas within your app).

See function comments for more details.

Change-Id: I181684b916e91d965e14849d8f83ec2c83e9a4a4

CMakeLists.txt

@@ -129,6 +129,105 @@ function(compile_flatbuffers_schema_to_binary SRC_FBS)
     DEPENDS flatc)
 endfunction()
 
+# General function to create FlatBuffer build rules for the given list of
+# schemas.
+#
+# flatbuffers_schemas: A list of flatbuffer schema files to process.
+#
+# schema_include_dirs: A list of schema file include directories, which will be
+# passed to flatc via the -I parameter.
+#
+# custom_target_name: The generated files will be added as dependencies for a
+# new custom target with this name. You should add that target as a dependency
+# for your main target to ensure these files are built.
+#
+# additional_dependencies: A list of additional dependencies that you'd like
+# all generated files to depend on. Pass in a blank string if you have none.
+#
+# generated_includes_dir: Where to generate the C++ header files for these
+# schemas. The generated includes directory will automatically be added to
+# CMake's include directories, and will be where generated header files are
+# placed. This parameter is optional; pass in empty string if you don't want to
+# generate include files for these schemas.
+#
+# binary_schemas_dir: If you specify an optional binary schema directory, binary
+# schemas will be generated for these schemas as well, and placed into the given
+# directory.
+#
+# copy_text_schemas_dir: If you want all text schemas (including schemas from
+# all schema include directories) copied into a directory (for example, if you
+# need them within your project to build JSON files), you can specify that
+# folder here. All text schemas will be copied to that folder.
+#
+# IMPORTANT: Make sure you quote all list arguments you pass to this function!
+# Otherwise CMake will only pass in the first element.
+# Example: build_flatbuffers("${fb_files}" "${include_dirs}" target_name ...)
+function(build_flatbuffers flatbuffers_schemas
+                           schema_include_dirs
+                           custom_target_name
+                           additional_dependencies
+                           generated_includes_dir
+                           binary_schemas_dir
+                           copy_text_schemas_dir)
+  set(schema_glob "*.fbs")
+  # Generate the include files parameters.
+  set(include_params "")
+  set(all_generated_files "")
+  foreach (include_dir ${schema_include_dirs})
+    set(include_params -I ${include_dir} ${include_params})
+    if (NOT ${copy_text_schemas_dir} STREQUAL "")
+      # Copy text schemas from dependent folders.
+      file(GLOB_RECURSE dependent_schemas ${include_dir}/${schema_glob})
+      foreach (dependent_schema ${dependent_schemas})
+        file(COPY ${dependent_schema} DESTINATION ${copy_text_schemas_dir})
+      endforeach()
+    endif()
+  endforeach()
+
+  # Register the include directory we are using.
+  if (NOT ${generated_includes_dir} STREQUAL "")
+    include_directories(${generated_includes_dir})
+  endif()
+
+  foreach(schema ${flatbuffers_schemas})
+    get_filename_component(filename ${schema} NAME_WE)
+    # For each schema, do the things we requested.
+    if (NOT ${generated_includes_dir} STREQUAL "")
+      set(generated_include ${generated_includes_dir}/${filename}_generated.h)
+      add_custom_command(
+        OUTPUT ${generated_include}
+        COMMAND flatc --gen-mutable
+        -o ${generated_includes_dir}
+        ${include_params}
+        -c ${schema}
+        DEPENDS flatc ${schema} ${additional_dependencies})
+      list(APPEND all_generated_files ${generated_include})
+    endif()
+
+    if (NOT ${binary_schemas_dir} STREQUAL "")
+      set(binary_schema ${binary_schemas_dir}/${filename}.bfbs)
+      add_custom_command(
+        OUTPUT ${binary_schema}
+        COMMAND flatc -b --schema
+        -o ${binary_schemas_dir}
+        ${include_params}
+        ${schema}
+        DEPENDS flatc ${schema} ${additional_dependencies})
+      list(APPEND all_generated_files ${binary_schema})
+    endif()
+
+    if (NOT ${copy_text_schemas_dir} STREQUAL "")
+      file(COPY ${schema} DESTINATION ${copy_text_schemas_dir})
+    endif()
+  endforeach()
+
+  # Create a custom target that depends on all the generated files.
+  # This is the target that you can depend on to trigger all these
+  # to be built.
+  add_custom_target(${custom_target_name}
+                    DEPENDS ${all_generated_files} ${additional_dependencies})
+endfunction()
+
 if(FLATBUFFERS_BUILD_TESTS)
   compile_flatbuffers_schema_to_cpp(tests/monster_test.fbs)
   include_directories(${CMAKE_CURRENT_BINARY_DIR}/tests)