Declare required_ruby_version 2.7 and run CI against Ruby 2.7 - 3.1, and minimum Rubocop version

.github/workflows/ruby.yml

@@ -4,6 +4,15 @@ on: [push, pull_request]
 
 jobs:
   build:
+    name: Ruby ${{matrix.ruby}} / ${{matrix.gemfile}}
+
+    strategy:
+      matrix:
+        gemfile: [Gemfile, gemfiles/minimum_rubocop.gemfile]
+        ruby: ["2.7", "3.0", "3.1"]
+
+    env:
+      BUNDLE_GEMFILE: ${{ matrix.gemfile }}
 
     runs-on: ubuntu-latest
 
@@ -12,6 +21,10 @@ jobs:
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
+        ruby-version: ${{ matrix.ruby }}
         bundler-cache: true
+    - name: Rubocop Version
+      if: ${{ matrix.gemfile == 'gemfiles/minimum_rubocop.gemfile' }}
+      run: bundle info rubocop | head -1
     - name: RuboCop and Tests
       run: bundle exec rake

.gitignore

@@ -3,3 +3,5 @@ _site
 node_modules
 css/
 pkg/
+
+gemfiles/*.gemfile.lock

Gemfile.lock

@@ -2,7 +2,7 @@ PATH
   remote: .
   specs:
     rubocop-shopify (2.5.0)
-      rubocop (~> 1.28)
+      rubocop (~> 1.29)
 
 GEM
   remote: https://rubygems.org/

gemfiles/minimum_rubocop.gemfile

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+eval_gemfile "../Gemfile"
+
+# This naively extracts the minimum rubocop version from our gemspec,
+# allowing us to ensure that it remains compatible.
+minimum_rubocop_version = File.read("rubocop-shopify.gemspec")[/(?<=add_dependency\("rubocop", "~> ).*(?="\)$)/]
+raise "Failed to extract minimum rubocop version from gemspec" if minimum_rubocop_version.nil?
+
+gem "rubocop", minimum_rubocop_version

rubocop-shopify.gemspec

@@ -21,5 +21,7 @@ Gem::Specification.new do |s|
     "allowed_push_host" => "https://rubygems.org",
   }
 
-  s.add_dependency("rubocop", "~> 1.28")
+  s.required_ruby_version = ">= 2.7.0"
+
+  s.add_dependency("rubocop", "~> 1.29")
 end

test/ruby_versions_test.rb

@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "pry"
+require "yaml"
+
+class RubyVersionsTest < Minitest::Test
+  def test_ci_matrix_includes_minimum_ruby_version
+    minimum_ruby_version = normalize(extract_minimum_ruby_version_from_gemspec)
+    ruby_versions = extract_ruby_versions_from_ci_matrix.map { |version| normalize(version) }
+
+    assert_includes(
+      ruby_versions,
+      minimum_ruby_version,
+      "CI must be configured to test as far back as gem's required_ruby_version",
+    )
+  end
+
+  private
+
+  def extract_minimum_ruby_version_from_gemspec
+    # This naively extracts the minimum Ruby version compatible with out gemspec
+    # allowing us to ensure that it is included in the CI matrix.
+    minimum_ruby_version = File.read("rubocop-shopify.gemspec")[/(?<=required_ruby_version = ">= ).*(?="$)/]
+
+    return minimum_ruby_version unless minimum_ruby_version.nil?
+
+    flunk("Failed to extract required_ruby_version from gemspec")
+  end
+
+  def extract_ruby_versions_from_ci_matrix
+    YAML
+      .load_file(".github/workflows/ruby.yml")
+      .fetch("jobs")
+      .fetch("build")
+      .fetch("strategy")
+      .fetch("matrix")
+      .fetch("ruby")
+  end
+
+  # Remove the trailing .0 for versions of the form X.Y.0
+  # Otherwise, return the version unchanged
+  def normalize(version)
+    if version.match?(/^\d+\.\d+\.0$/)
+      version.chomp(".0")
+    else
+      version
+    end
+  end
+end