Introduce 'suspenders:lint` generator

Closes #1107
Closes #1143

Creates a holistic linting solution that covers JavaScript, CSS, Ruby
and ERB.

Introduces `eslint` and `stylelint` NPM commands that leverage
[@thoughtbot/eslint-config][] and [@thoughtbot/stylelint-config][].

```
yarn run eslint
yarn run stylelint
```

Also introduces `.prettierrc` based off of our [Guides][].

[@thoughtbot/eslint-config]: https://github.com/thoughtbot/eslint-config
[@thoughtbot/stylelint-config]: https://github.com/thoughtbot/stylelint-config
[Guides]: https://github.com/thoughtbot/guides/blob/main/javascript/README.md#formatting

Introduces `rake standard` which also runs `erblint` to lint ERB files
via [better_html][], [erb_lint][] and [erblint-github][].

[better_html]: https://github.com/Shopify/better-html
[erb_lint]: https://github.com/Shopify/erb-lint
[erblint-github]: https://github.com/github/erblint-github

A future commit will ensure these linting rules are run during CI.

It should be noted that we deliberately permit this generator to be
invoked on API only applications, because those applications can still
contain views, like ones used for mailers.

Also improves the developer experience by introducing `with_test_suite`
helper, allowing the caller to run the generator in an application using
minitest or RSpec.

README.md

@@ -72,6 +72,30 @@ improvement for the viewer.
 
   [inline_svg]: https://github.com/jamesmartin/inline_svg
 
+### Lint
+
+Creates a holistic linting solution that covers JavaScript, CSS, Ruby and ERB.
+
+Introduces `eslint` and `stylelint` NPM commands that leverage
+[@thoughtbot/eslint-config][] and [@thoughtbot/stylelint-config][].
+
+```
+yarn run eslint
+yarn run stylelint
+```
+
+Also introduces `.prettierrc` based off of our [Guides][].
+
+Introduces `rake standard` which also runs `erblint` to lint ERB files
+via [better_html][], [erb_lint][] and [erblint-github][].
+
+[@thoughtbot/eslint-config]: https://github.com/thoughtbot/eslint-config
+[@thoughtbot/stylelint-config]: https://github.com/thoughtbot/stylelint-config
+[Guides]: https://github.com/thoughtbot/guides/blob/main/javascript/README.md#formatting
+[better_html]: https://github.com/Shopify/better-html
+[erb_lint]: https://github.com/Shopify/erb-lint
+[erblint-github]: https://github.com/github/erblint-github
+
 ### Styles
 
 Configures applications to use [PostCSS][] or [Tailwind][] via

lib/generators/suspenders/lint_generator.rb

@@ -0,0 +1,67 @@
+module Suspenders
+  module Generators
+    class LintGenerator < Rails::Generators::Base
+      include Suspenders::Generators::Helpers
+
+      source_root File.expand_path("../../templates/lint", __FILE__)
+      desc "Creates a holistic linting solution that covers JavaScript, CSS, Ruby and ERB."
+
+      def install_dependencies
+        run "yarn add stylelint eslint @thoughtbot/stylelint-config @thoughtbot/eslint-config --dev"
+      end
+
+      def install_gems
+        gem_group :development, :test do
+          gem "better_html", require: false
+          gem "erb_lint", require: false
+          gem "erblint-github", require: false
+          gem "standard"
+        end
+        Bundler.with_unbundled_env { run "bundle install" }
+      end
+
+      def configure_stylelint
+        copy_file "stylelintrc.json", ".stylelintrc.json"
+      end
+
+      def configure_eslint
+        copy_file "eslintrc.json", ".eslintrc.json"
+      end
+
+      def configure_prettier
+        copy_file "prettierrc", ".prettierrc"
+      end
+
+      def configure_erb_lint
+        copy_file "erb-lint.yml", ".erb-lint.yml"
+        copy_file "config_better_html.yml", "config/better_html.yml"
+        copy_file "config_initializers_better_html.rb", "config/initializers/better_html.rb"
+        copy_file "erblint.rake", "lib/tasks/erblint.rake"
+
+        if default_test_suite?
+          copy_file "better_html_test.rb", "test/views/better_html_test.rb"
+        elsif rspec_test_suite?
+          copy_file "better_html_spec.rb", "spec/views/better_html_spec.rb"
+        end
+      end
+
+      # TODO: Consider extracting this into Rails
+      def update_package_json
+        content = File.read package_json
+        json = JSON.parse content
+        json["scripts"] ||= {}
+
+        json["scripts"]["eslint"] = "npx eslint 'app/javascript/**/*.js'"
+        json["scripts"]["stylelint"] = "npx stylelint 'app/assets/stylesheets/**/*.css'"
+
+        File.write package_json, JSON.pretty_generate(json)
+      end
+
+      private
+
+      def package_json
+        Rails.root.join("package.json")
+      end
+    end
+  end
+end

lib/generators/templates/lint/better_html_spec.rb

@@ -0,0 +1,17 @@
+require "spec_helper"
+
+describe "ERB Implementation" do
+  def self.erb_lint
+    configuration = ActiveSupport::ConfigurationFile.parse(".erb-lint.yml")
+
+    ActiveSupport::OrderedOptions.new.merge!(configuration.deep_symbolize_keys!)
+  end
+
+  Rails.root.glob(erb_lint.glob).each do |template|
+    it "raises html errors in #{template.relative_path_from(Rails.root)}" do
+      validator = BetterHtml::BetterErb::ErubiImplementation.new(template.read)
+
+      validator.validate!
+    end
+  end
+end

lib/generators/templates/lint/better_html_test.rb

@@ -0,0 +1,17 @@
+require "test_helper"
+
+class ErbImplementationTest < ActiveSupport::TestCase
+  def self.erb_lint
+    configuration = ActiveSupport::ConfigurationFile.parse(".erb-lint.yml")
+
+    ActiveSupport::OrderedOptions.new.merge!(configuration.deep_symbolize_keys!)
+  end
+
+  Rails.root.glob(erb_lint.glob).each do |template|
+    test "html errors in #{template.relative_path_from(Rails.root)}" do
+      validator = BetterHtml::BetterErb::ErubiImplementation.new(template.read)
+
+      validator.validate!
+    end
+  end
+end

lib/generators/templates/lint/config_better_html.yml

@@ -0,0 +1,2 @@
+---
+allow_single_quoted_attributes: false

lib/generators/templates/lint/config_initializers_better_html.rb

@@ -0,0 +1,5 @@
+Rails.configuration.to_prepare do
+  config = ActiveSupport::ConfigurationFile.parse("config/better_html.yml")
+
+  BetterHtml.config = BetterHtml::Config.new(config)
+end

lib/generators/templates/lint/erb-lint.yml

@@ -0,0 +1,63 @@
+---
+glob: "app/views/**/*.{html,turbo_stream}{+*,}.erb"
+
+linters:
+  AllowedScriptType:
+    enabled: true
+    allowed_types:
+      - "module"
+      - "text/javascript"
+  ErbSafety:
+    enabled: true
+    better_html_config: "config/better_html.yml"
+  GitHub::Accessibility::AvoidBothDisabledAndAriaDisabledCounter:
+    enabled: true
+  GitHub::Accessibility::AvoidGenericLinkTextCounter:
+    enabled: true
+  GitHub::Accessibility::DisabledAttributeCounter:
+    enabled: true
+  GitHub::Accessibility::IframeHasTitleCounter:
+    enabled: true
+  GitHub::Accessibility::ImageHasAltCounter:
+    enabled: true
+  GitHub::Accessibility::LandmarkHasLabelCounter:
+    enabled: true
+  GitHub::Accessibility::LinkHasHrefCounter:
+    enabled: true
+  GitHub::Accessibility::NestedInteractiveElementsCounter:
+    enabled: true
+  GitHub::Accessibility::NoAriaLabelMisuseCounter:
+    enabled: true
+  GitHub::Accessibility::NoPositiveTabIndexCounter:
+    enabled: true
+  GitHub::Accessibility::NoRedundantImageAltCounter:
+    enabled: true
+  GitHub::Accessibility::NoTitleAttributeCounter:
+    enabled: true
+  GitHub::Accessibility::SvgHasAccessibleTextCounter:
+    enabled: true
+  Rubocop:
+    enabled: true
+    rubocop_config:
+      inherit_from:
+        - .rubocop.yml
+
+      Lint/EmptyBlock:
+        Enabled: false
+      Layout/InitialIndentation:
+        Enabled: false
+      Layout/TrailingEmptyLines:
+        Enabled: false
+      Layout/TrailingWhitespace:
+        Enabled: false
+      Layout/LeadingEmptyLines:
+        Enabled: false
+      Style/FrozenStringLiteralComment:
+        Enabled: false
+      Style/MultilineTernaryOperator:
+        Enabled: false
+      Lint/UselessAssignment:
+        Exclude:
+          - "app/views/**/*"
+
+EnableDefaultLinters: true

lib/generators/templates/lint/erblint.rake

@@ -0,0 +1,47 @@
+module ERBLint
+  module RakeSupport
+    # Allow command line flags set in STANDARDOPTS (like MiniTest's TESTOPTS)
+    def self.argvify
+      if ENV["ERBLINTOPTS"]
+        ENV["ERBLINTOPTS"].split(/\s+/)
+      else
+        []
+      end
+    end
+
+    # DELETE THIS FILE AFTER MERGE:
+    #
+    #   * https://github.com/Shopify/better-html/pull/95
+    #
+    def self.backport!
+      BetterHtml::TestHelper::SafeErb::AllowedScriptType::VALID_JAVASCRIPT_TAG_TYPES.push("module")
+    end
+  end
+end
+
+desc "Lint templates with erb_lint"
+task "erblint" do
+  require "erb_lint/cli"
+  require "erblint-github/linters"
+
+  ERBLint::RakeSupport.backport!
+
+  cli = ERBLint::CLI.new
+  success = cli.run(ERBLint::RakeSupport.argvify + ["--lint-all", "--format=compact"])
+  fail unless success
+end
+
+desc "Lint and automatically fix templates with erb_lint"
+task "erblint:autocorrect" do
+  require "erb_lint/cli"
+  require "erblint-github/linters"
+
+  ERBLint::RakeSupport.backport!
+
+  cli = ERBLint::CLI.new
+  success = cli.run(ERBLint::RakeSupport.argvify + ["--lint-all", "--autocorrect"])
+  fail unless success
+end
+
+task "standard" => "erblint"
+task "standard:fix" => "erblint:autocorrect"

lib/generators/templates/lint/eslintrc.json

@@ -0,0 +1,6 @@
+{
+  "extends": [
+    "@thoughtbot/eslint-config/base",
+    "@thoughtbot/eslint-config/prettier"
+  ]
+}

lib/generators/templates/lint/prettierrc

@@ -0,0 +1,3 @@
+{
+  "singleQuote": true
+}

lib/generators/templates/lint/stylelintrc.json

@@ -0,0 +1,3 @@
+{
+  "extends": "@thoughtbot/stylelint-config"
+}