[Ruby] Add initial Ruby implementation

This supports only reading FlatBuffers data.

I confirmed that this implementation works for
`reflection/reflection.bfbs` and `tests/monsterdata_test.mon`. This
includes tests for them in `tests/ruby/`. `tests/RubyTest.rb` is a
test runner.

Other `.rb` files in `tests/` are auto generated files by
`scripts/generate_code.py`. I followed the suggestion in the pull
request template.

I'll work on the following tasks after this is merged:

* Add support for writing FlatBuffers data.
* Prepare RubyGems package.

Author: kou

.github/workflows/build.yml

@@ -594,6 +594,31 @@ jobs:
       working-directory: tests/nim
       run: python3 testnim.py
 
+  build-ruby:
+    name: Build Ruby
+    runs-on: ubuntu-24.04
+    steps:
+    - uses: actions/checkout@v5
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ruby
+    - name: flatc
+      run: |
+        cmake \
+          -S . \
+          -B build \
+          -G Ninja \
+          -DCMAKE_BUILD_TYPE=Release \
+          -DFLATBUFFERS_BUILD_FLATHASH=OFF \
+          -DFLATBUFFERS_BUILD_FLATLIB=OFF \
+          -DFLATBUFFERS_BUILD_TESTS=OFF \
+          -DFLATBUFFERS_INSTALL=OFF \
+          -DFLATBUFFERS_STRICT_MODE=ON
+        ninja -C build
+    - name: test
+      run: |
+        BUILD_DIR=build tests/RubyTest.rb
+
   bazel:
     name: Bazel
     runs-on: ubuntu-24.04

CMakeLists.txt

@@ -183,6 +183,7 @@ set(FlatBuffers_Compiler_SRCS
   src/bfbs_gen.h
   src/bfbs_gen_lua.h
   src/bfbs_gen_nim.h
+  src/bfbs_gen_ruby.h
   src/bfbs_namer.h
   include/codegen/idl_namer.h
   include/codegen/namer.h
@@ -195,6 +196,7 @@ set(FlatBuffers_Compiler_SRCS
   src/annotated_binary_text_gen.cpp
   src/bfbs_gen_lua.cpp
   src/bfbs_gen_nim.cpp
+  src/bfbs_gen_ruby.cpp
   src/code_generators.cpp
   grpc/src/compiler/schema_interface.h
   grpc/src/compiler/cpp_generator.h

include/flatbuffers/idl.h

@@ -753,6 +753,7 @@ struct IDLOptions {
     kNim = 1 << 17,
     kProto = 1 << 18,
     kKotlinKmp = 1 << 19,
+    kRuby = 1 << 20,
     kMAX
   };
 

ruby/flatbuffers.rb

@@ -0,0 +1,20 @@
+# Copyright 2025 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require_relative "flatbuffers/enum"
+require_relative "flatbuffers/flags"
+require_relative "flatbuffers/struct"
+require_relative "flatbuffers/table"
+require_relative "flatbuffers/union"
+require_relative "flatbuffers/version"

ruby/flatbuffers/enum.rb

@@ -0,0 +1,49 @@
+# Copyright 2025 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+module FlatBuffers
+  class Enum
+    class << self
+      def try_convert(value)
+        case value
+        when Symbol, String
+          @name_to_enum[value.to_s]
+        when Integer
+          @value_to_enum[value]
+        when self
+          value
+        else
+          nil
+        end
+      end
+
+      def register(name, value)
+        object = new(name, value)
+        (@name_to_enum ||= {})[name] = object
+        (@value_to_enum ||= {})[value] = object
+        object
+      end
+    end
+
+    attr_reader :name
+    attr_reader :value
+    def initialize(name, value)
+      @name = name
+      @value = value
+    end
+
+    alias_method :to_i, :value
+    alias_method :to_int, :value
+  end
+end

ruby/flatbuffers/flags.rb

@@ -0,0 +1,69 @@
+# Copyright 2025 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+module FlatBuffers
+  class Flags
+    class << self
+      def try_convert(value)
+        case value
+        when Array
+          value.inject(new) do |previous, v|
+            flag = try_convert(v)
+            return nil if flag.nil?
+            previous | flag
+          end
+        when Symbol, String
+          try_convert(@name_to_value[value.to_s])
+        when Integer
+          new(value)
+        when self
+          value
+        else
+          nil
+        end
+      end
+
+      def register(name, value)
+        (@name_to_value ||= {})[name] = value
+        new(value)
+      end
+
+      def names
+        @name_to_value.keys
+      end
+
+      def resolve_names(value)
+        @name_to_value.select do |name, v|
+          not (value & v).zero?
+        end
+      end
+    end
+
+    attr_reader :value
+    def initialize(value=0)
+      @value = value
+    end
+
+    def names
+      @names ||= self.class.resolve_names(@value)
+    end
+
+    alias_method :to_i, :value
+    alias_method :to_int, :value
+
+    def |(other)
+      self.class.new(@value | Integer(other))
+    end
+  end
+end

ruby/flatbuffers/inspectable.rb

@@ -0,0 +1,41 @@
+# Copyright 2025 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+module FlatBuffers
+  module Inspectable
+    def inspect
+      inspected = +"<#{self.class}:"
+      public_methods(false).each do |name|
+        next unless method(name).arity.zero?
+        inspected << " #{name}=#{__send__(name).inspect}"
+      end
+      inspected << ">"
+      inspected
+    end
+
+    def pretty_print(q)
+      q.object_group(self) do
+        targets = public_methods(false).select do |name|
+          method(name).arity.zero?
+        end
+        q.seplist(targets, lambda {q.text(",")}) do |name|
+          q.breakable
+          q.text(name.to_s)
+          q.text("=")
+          q.pp(__send__(name))
+        end
+      end
+    end
+  end
+end

ruby/flatbuffers/struct.rb

@@ -0,0 +1,26 @@
+# Copyright 2025 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require_relative "inspectable"
+require_relative "view"
+
+module FlatBuffers
+  class Struct
+    include Inspectable
+
+    def initialize(view)
+      @view = view
+    end
+  end
+end

ruby/flatbuffers/table.rb

@@ -0,0 +1,34 @@
+# Copyright 2025 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+require_relative "inspectable"
+require_relative "view"
+
+module FlatBuffers
+  class Table
+    include Inspectable
+
+    def initialize(input)
+      if input.is_a?(View)
+        @view = input
+      else
+        if input.is_a?(String)
+          input = IO::Buffer.for(input)
+        end
+        offset = input.get_value(:u32, 0)
+        @view = View.new(input, offset, have_vtable: true)
+      end
+    end
+  end
+end

ruby/flatbuffers/union.rb

@@ -0,0 +1,62 @@
+# Copyright 2025 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+module FlatBuffers
+  class Union
+    class << self
+      def try_convert(value)
+        case value
+        when Symbol, String
+          @name_to_union[value.to_s]
+        when Integer
+          @value_to_union[value]
+        when self
+          value
+        else
+          nil
+        end
+      end
+
+      def register(name, value, table_class_name, require_path)
+        object = new(name, value, table_class_name, require_path)
+        (@name_to_union ||= {})[name] = object
+        (@value_to_union ||= {})[value] = object
+        object
+      end
+    end
+
+    attr_reader :name
+    attr_reader :value
+    def initialize(name, value, table_class_name, require_path)
+      @name = name
+      @value = value
+      @table_class_name = table_class_name
+      @require_path = require_path
+    end
+
+    def table_class
+      @table_class ||= resolve_table_class
+    end
+
+    private def resolve_table_class
+      return nil if @table_class_name.nil?
+
+      require_table_class
+      Object.const_get(@table_class_name)
+    end
+
+    alias_method :to_i, :value
+    alias_method :to_int, :value
+  end
+end