Add CI env for C++

This is a follow up of ruby#443

.github/workflows/test.yaml

@@ -54,6 +54,24 @@ jobs:
       - run: flex --help
       - run: bundle install
       - run: bundle exec rspec
+  test-cpp:
+    needs: ruby-versions
+    runs-on: ubuntu-20.04
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby: ['head']
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
+      - run: flex --help
+      - run: bundle install
+      - run: bundle exec rspec
+        env:
+          COMPILER: 'c++'
   test-memory:
     runs-on: ubuntu-20.04
     strategy:

spec/lrama/integration_spec.rb

@@ -9,6 +9,10 @@ def exec_command(command)
       raise "#{command} failed." unless $?.success?
     end
 
+    def compiler
+      ENV['COMPILER'] || "gcc"
+    end
+
     def test_parser(parser_name, input, expected, expect_success: true, lrama_command_args: [], debug: false)
       tmpdir = Dir.tmpdir
       grammar_file_path = fixture_path("integration/#{parser_name}.y")
@@ -27,7 +31,7 @@ def test_parser(parser_name, input, expected, expect_success: true, lrama_comman
 
       Lrama::Command.new.run(%W[-H#{parser_h_path} -o#{parser_c_path}] + lrama_command_args + %W[#{grammar_file_path}])
       exec_command("flex --header-file=#{lexer_h_path} -o #{lexer_c_path} #{lexer_file_path}")
-      exec_command("gcc -Wall -ggdb3 -I#{tmpdir} #{parser_c_path} #{lexer_c_path} -o #{obj_path}")
+      exec_command("#{compiler} -Wall -ggdb3 -I#{tmpdir} #{parser_c_path} #{lexer_c_path} -o #{obj_path}")
 
       out = err = status = nil
 
@@ -48,7 +52,7 @@ def test_parser(parser_name, input, expected, expect_success: true, lrama_comman
 
     def generate_object(grammar_file_path, c_path, obj_path, command_args: [])
       Lrama::Command.new.run(%W[-d -o #{c_path}] + command_args + %W[#{grammar_file_path}])
-      exec_command("gcc -Wall #{c_path} -o #{obj_path}")
+      exec_command("#{compiler} -Wall #{c_path} -o #{obj_path}")
     end
   end