Migrate accessibility rubocop rule NoRedundantImageAlt from dotcom to erblint-github

lib/rubocop/cop/github/rails_no_redundant_image_alt.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require "rubocop"
+
+module RuboCop
+  module Cop
+    module GitHub
+      module Accessibility
+        class NoRedundantImageAlt < Base
+          MSG = "Alt prop should not contain `image` or `picture` as screen readers already announce the element as an image"
+          REDUNDANT_ALT_WORDS = %w(image picture)
+
+          def_node_search :redundant_alt?, "(pair (sym :alt) (str #contains_redundant_alt_text?))"
+
+          def on_send(node)
+            receiver, method_name, _= *node
+
+            if receiver.nil? && method_name == :image_tag
+              if redundant_alt?(node)
+                add_offense(node.loc.selector)
+              end
+            end
+          end
+
+          private
+
+          def contains_redundant_alt_text?(string)
+            return false if string.empty?
+
+            if (string.downcase.split & REDUNDANT_ALT_WORDS).any?
+              return true
+            end
+          end
+        end
+      end
+    end
+  end
+end

test/test_rails_no_redundant_image_alt.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+require_relative "./cop_test"
+require "minitest/autorun"
+require "rubocop/cop/github/rails_no_redundant_image_alt"
+
+class NoRedundantImageAlt < CopTest
+  def cop_class
+    RuboCop::Cop::GitHub::Accessibility::NoRedundantImageAlt
+  end
+
+  def test_no_redundant_image_alt_offense
+    offenses = erb_investigate cop, <<-ERB, "app/views/products/index.html.erb"
+      <%= image_tag "cat.gif", size: "12x12", alt: "Picture of a cat" %>
+    ERB
+
+    assert_equal 1, offenses.count
+    assert_equal "Alt prop should not contain `image` or `picture` as screen readers already announce the element as an image", offenses[0].message
+  end
+
+  def test_no_redundant_image_alt_no_offense
+    offenses = erb_investigate cop, <<-ERB, "app/views/products/index.html.erb"
+       <%= image_tag "cat.gif", size: "12x12", alt: "A black cat" %>
+    ERB
+
+    assert_equal 0, offenses.count
+  end
+end