mruby: initialize Bundler project and add RuboCop

pkgs/mruby/.gitignore

@@ -1 +1,7 @@
 /build_config.rb.lock
+
+# For a library or gem, you might want to ignore these files since the code is
+# intended to run in multiple environments; otherwise, check them in.
+/Gemfile.lock
+/.ruby-version
+/.ruby-gemset

pkgs/mruby/.rubocop.yml

@@ -0,0 +1,56 @@
+require:
+  - rubocop-performance
+  - rubocop-rake
+
+AllCops:
+  TargetRubyVersion: 3.0
+  DisplayCopNames: true
+  NewCops: enable
+
+Layout/AccessModifierIndentation:
+  EnforcedStyle: outdent
+
+Layout/LineLength:
+  Max: 80
+
+Lint/AmbiguousOperatorPrecedence:
+  Enabled: false
+
+Lint/ReturnInVoidContext:
+  Enabled: false
+
+Metrics/BlockLength:
+  Exclude:
+    - 'Rakefile'
+    - 'test/**/*.rb'
+
+Style/AndOr:
+  EnforcedStyle: conditionals
+
+Style/Documentation:
+  Exclude:
+    - 'Rakefile'
+
+Style/DoubleNegation:
+  Enabled: false
+
+Style/FrozenStringLiteralComment:
+  Enabled: false
+
+Style/HashAsLastArrayItem:
+  Enabled: false
+
+Style/PerlBackrefs:
+  Enabled: false
+
+Style/TrailingCommaInArguments:
+  EnforcedStyleForMultiline: comma
+
+Style/TrailingCommaInArrayLiteral:
+  EnforcedStyleForMultiline: comma
+
+Style/TrailingCommaInHashLiteral:
+  EnforcedStyleForMultiline: comma
+
+Style/VariableInterpolation:
+  Enabled: false

pkgs/mruby/Gemfile

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+source 'https://rubygems.org'
+
+gem 'bundler',             '~> 2.2'
+gem 'rake',                '~> 13.0'
+gem 'rubocop',             '~> 1.25'
+gem 'rubocop-performance', '~> 1.13'
+gem 'rubocop-rake',        '~> 0.6'

pkgs/mruby/Rakefile

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+desc 'Run default checks'
+task default: :lint
+
+desc 'Run code analysis tools'
+task lint: :rubocop
+
+desc 'Fix code style (rubocop --auto-correct)'
+task fix: 'rubocop:auto_correct'
+
+begin
+  require 'rubocop/rake_task'
+  RuboCop::RakeTask.new
+rescue LoadError
+  nil
+end

pkgs/mruby/bin/setup

@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+bundle install
+
+# Do any other automated setup that you need to do here