Do not generate default alt text in image tags

- Auto-generating content from the filename of an image is not suitable
  alternative text; alt text that isn't fully considered can be
  distracting and fatiguing for screen readers users (blind, low vision,
  dyslexic people).
- Setting a filename fallback short circuits screen reader default
  behavior and configuration for blank descriptions.
- Setting poor defaults also creates false negatives for accessibility
  linting and testing software, that makes it harder to improve
  application accessibility.

***

- After this change, if authors leave images without alt text, screen
  readers will fallback to default behavior for missing alt text.
- Also with this change, Automated linting and testing tools will
  correctly generate warnings.

[Fixes #30096]

actionmailer/test/asset_host_test.rb

@@ -24,7 +24,7 @@ def teardown

  def test_asset_host_as_string
    mail = AssetHostMailer.email_with_asset
    assert_dom_equal '<img alt="Somelogo" src="http://www.example.com/images/somelogo.png" />', mail.body.to_s.strip
    assert_dom_equal '<img src="http://www.example.com/images/somelogo.png" />', mail.body.to_s.strip
  end

  def test_asset_host_as_one_argument_proc
@@ -34,6 +34,6 @@ def test_asset_host_as_one_argument_proc
      end
    }
    mail = AssetHostMailer.email_with_asset
    assert_dom_equal '<img alt="Somelogo" src="http://images.example.com/images/somelogo.png" />', mail.body.to_s.strip
    assert_dom_equal '<img src="http://images.example.com/images/somelogo.png" />', mail.body.to_s.strip
  end
end

actionmailer/test/base_test.rb

@@ -578,7 +578,7 @@ def welcome

    mail = AssetMailer.welcome

    assert_dom_equal(%{<img alt="Dummy" src="http://global.com/images/dummy.png" />}, mail.body.to_s.strip)
    assert_dom_equal(%{<img src="http://global.com/images/dummy.png" />}, mail.body.to_s.strip)
  end

  test "assets tags should use a Mailer's asset_host settings when available" do
@@ -592,7 +592,7 @@ def welcome

    mail = TempAssetMailer.welcome

    assert_dom_equal(%{<img alt="Dummy" src="http://local.com/images/dummy.png" />}, mail.body.to_s.strip)
    assert_dom_equal(%{<img src="http://local.com/images/dummy.png" />}, mail.body.to_s.strip)
  end

  test "the view is not rendered when mail was never called" do

actionmailer/test/url_test.rb

@@ -121,7 +121,7 @@ def test_signed_up_with_url
    expected = new_mail
    expected.to      = @recipient
    expected.subject = "[Signed up] Welcome #{@recipient}"
    expected.body    = "Hello there,\n\nMr. #{@recipient}. Please see our greeting at http://example.com/welcome/greeting http://www.basecamphq.com/welcome\n\n<img alt=\"Somelogo\" src=\"/images/somelogo.png\" />"
    expected.body    = "Hello there,\n\nMr. #{@recipient}. Please see our greeting at http://example.com/welcome/greeting http://www.basecamphq.com/welcome\n\n<img src=\"/images/somelogo.png\" />"
    expected.from    = "system@loudthinking.com"
    expected.date    = Time.local(2004, 12, 12)
    expected.content_type = "text/html"

actionview/CHANGELOG.md

@@ -1,3 +1,9 @@
*   Remove default `alt` text generation.

    Fixes #30096

    *Cameron Cundiff*

*   Add `srcset` option to `image_tag` helper.

    *Roberto Miranda*

actionview/lib/action_view/helpers/asset_tag_helper.rb

@@ -13,7 +13,7 @@ module Helpers #:nodoc:
    # the assets exist before linking to them:
    #
    #   image_tag("rails.png")
    #   # => <img alt="Rails" src="/assets/rails.png" />
    #   # => <img src="/assets/rails.png" />
    #   stylesheet_link_tag("application")
    #   # => <link href="/assets/application.css?body=1" media="screen" rel="stylesheet" />
    module AssetTagHelper
@@ -207,8 +207,6 @@ def favicon_link_tag(source = "favicon.ico", options = {})
      # You can add HTML attributes using the +options+. The +options+ supports
      # additional keys for convenience and conformance:
      #
      # * <tt>:alt</tt>  - If no alt text is given, the file name part of the
      #   +source+ is used (capitalized and without the extension)
      # * <tt>:size</tt> - Supplied as "{Width}x{Height}" or "{Number}", so "30x45" becomes
      #   width="30" and height="45", and "50" becomes width="50" and height="50".
      #   <tt>:size</tt> will be ignored if the value is not in the correct format.
@@ -220,17 +218,17 @@ def favicon_link_tag(source = "favicon.ico", options = {})
      # Assets (images that are part of your app):
      #
      #   image_tag("icon")
      #   # => <img alt="Icon" src="/assets/icon" />
      #   # => <img src="/assets/icon" />
      #   image_tag("icon.png")
      #   # => <img alt="Icon" src="/assets/icon.png" />
      #   # => <img src="/assets/icon.png" />
      #   image_tag("icon.png", size: "16x10", alt: "Edit Entry")
      #   # => <img src="/assets/icon.png" width="16" height="10" alt="Edit Entry" />
      #   image_tag("/icons/icon.gif", size: "16")
      #   # => <img src="/icons/icon.gif" width="16" height="16" alt="Icon" />
      #   # => <img src="/icons/icon.gif" width="16" height="16" />
      #   image_tag("/icons/icon.gif", height: '32', width: '32')
      #   # => <img alt="Icon" height="32" src="/icons/icon.gif" width="32" />
      #   # => <img height="32" src="/icons/icon.gif" width="32" />
      #   image_tag("/icons/icon.gif", class: "menu_icon")
      #   # => <img alt="Icon" class="menu_icon" src="/icons/icon.gif" />
      #   # => <img class="menu_icon" src="/icons/icon.gif" />
      #   image_tag("/icons/icon.gif", data: { title: 'Rails Application' })
      #   # => <img data-title="Rails Application" src="/icons/icon.gif" />
      #   image_tag("icon.png", srcset: { "icon_2x.png" => "2x", "icon_4x.png" => "4x" })
@@ -251,11 +249,7 @@ def image_tag(source, options = {})
        check_for_image_tag_errors(options)
        skip_pipeline = options.delete(:skip_pipeline)

        src = options[:src] = resolve_image_source(source, skip_pipeline)

        unless src.start_with?("cid:") || src.start_with?("data:") || src.blank?
          options[:alt] = options.fetch(:alt) { image_alt(src) }
        end
        options[:src] = resolve_image_source(source, skip_pipeline)

        if options[:srcset] && !options[:srcset].is_a?(String)
          options[:srcset] = options[:srcset].map do |src_path, size|
@@ -286,6 +280,8 @@ def image_tag(source, options = {})
      #   image_alt('underscored_file_name.png')
      #   # => Underscored file name
      def image_alt(src)
        ActiveSupport::Deprecation.warn("image_alt is deprecated and will be removed from Rails 6.0. You must explicitly set alt text on images.")

        File.basename(src, ".*".freeze).sub(/-[[:xdigit:]]{32,64}\z/, "".freeze).tr("-_".freeze, " ".freeze).capitalize
      end

actionview/test/template/asset_tag_helper_test.rb

@@ -183,26 +183,26 @@ def url_for(*args)
  }

  ImageLinkToTag = {
    %(image_tag("xml.png")) => %(<img alt="Xml" src="/images/xml.png" />),
    %(image_tag("xml.png")) => %(<img src="/images/xml.png" />),
    %(image_tag("rss.gif", :alt => "rss syndication")) => %(<img alt="rss syndication" src="/images/rss.gif" />),
    %(image_tag("gold.png", :size => "20")) => %(<img alt="Gold" height="20" src="/images/gold.png" width="20" />),
    %(image_tag("gold.png", :size => 20)) => %(<img alt="Gold" height="20" src="/images/gold.png" width="20" />),
    %(image_tag("gold.png", :size => "45x70")) => %(<img alt="Gold" height="70" src="/images/gold.png" width="45" />),
    %(image_tag("gold.png", "size" => "45x70")) => %(<img alt="Gold" height="70" src="/images/gold.png" width="45" />),
    %(image_tag("error.png", "size" => "45 x 70")) => %(<img alt="Error" src="/images/error.png" />),
    %(image_tag("error.png", "size" => "x")) => %(<img alt="Error" src="/images/error.png" />),
    %(image_tag("google.com.png")) => %(<img alt="Google.com" src="/images/google.com.png" />),
    %(image_tag("slash..png")) => %(<img alt="Slash." src="/images/slash..png" />),
    %(image_tag(".pdf.png")) => %(<img alt=".pdf" src="/images/.pdf.png" />),
    %(image_tag("http://www.rubyonrails.com/images/rails.png")) => %(<img alt="Rails" src="http://www.rubyonrails.com/images/rails.png" />),
    %(image_tag("//www.rubyonrails.com/images/rails.png")) => %(<img alt="Rails" src="//www.rubyonrails.com/images/rails.png" />),
    %(image_tag("gold.png", :size => "20")) => %(<img height="20" src="/images/gold.png" width="20" />),
    %(image_tag("gold.png", :size => 20)) => %(<img height="20" src="/images/gold.png" width="20" />),
    %(image_tag("gold.png", :size => "45x70")) => %(<img height="70" src="/images/gold.png" width="45" />),
    %(image_tag("gold.png", "size" => "45x70")) => %(<img height="70" src="/images/gold.png" width="45" />),
    %(image_tag("error.png", "size" => "45 x 70")) => %(<img src="/images/error.png" />),
    %(image_tag("error.png", "size" => "x")) => %(<img src="/images/error.png" />),
    %(image_tag("google.com.png")) => %(<img src="/images/google.com.png" />),
    %(image_tag("slash..png")) => %(<img src="/images/slash..png" />),
    %(image_tag(".pdf.png")) => %(<img src="/images/.pdf.png" />),
    %(image_tag("http://www.rubyonrails.com/images/rails.png")) => %(<img src="http://www.rubyonrails.com/images/rails.png" />),
    %(image_tag("//www.rubyonrails.com/images/rails.png")) => %(<img src="//www.rubyonrails.com/images/rails.png" />),
    %(image_tag("mouse.png", :alt => nil)) => %(<img src="/images/mouse.png" />),
    %(image_tag("data:image/gif;base64,R0lGODlhAQABAID/AMDAwAAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==", :alt => nil)) => %(<img src="data:image/gif;base64,R0lGODlhAQABAID/AMDAwAAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==" />),
    %(image_tag("")) => %(<img src="" />),
    %(image_tag("gold.png", data: { title: 'Rails Application' })) => %(<img data-title="Rails Application" src="/images/gold.png" alt="Gold" />),
    %(image_tag("rss.gif", srcset: "/assets/pic_640.jpg 640w, /assets/pic_1024.jpg 1024w")) => %(<img srcset="/assets/pic_640.jpg 640w, /assets/pic_1024.jpg 1024w" src="/images/rss.gif" alt="Rss" />),
    %(image_tag("rss.gif", srcset: { "pic_640.jpg" => "640w", "pic_1024.jpg" => "1024w" })) => %(<img srcset="/images/pic_640.jpg 640w, /images/pic_1024.jpg 1024w" src="/images/rss.gif" alt="Rss" />),
    %(image_tag("rss.gif", srcset: [["pic_640.jpg", "640w"], ["pic_1024.jpg", "1024w"]])) => %(<img srcset="/images/pic_640.jpg 640w, /images/pic_1024.jpg 1024w" src="/images/rss.gif" alt="Rss" />)
    %(image_tag("gold.png", data: { title: 'Rails Application' })) => %(<img data-title="Rails Application" src="/images/gold.png" />),
    %(image_tag("rss.gif", srcset: "/assets/pic_640.jpg 640w, /assets/pic_1024.jpg 1024w")) => %(<img srcset="/assets/pic_640.jpg 640w, /assets/pic_1024.jpg 1024w" src="/images/rss.gif" />),
    %(image_tag("rss.gif", srcset: { "pic_640.jpg" => "640w", "pic_1024.jpg" => "1024w" })) => %(<img srcset="/images/pic_640.jpg 640w, /images/pic_1024.jpg 1024w" src="/images/rss.gif" />),
    %(image_tag("rss.gif", srcset: [["pic_640.jpg", "640w"], ["pic_1024.jpg", "1024w"]])) => %(<img srcset="/images/pic_640.jpg 640w, /images/pic_1024.jpg 1024w" src="/images/rss.gif" />)
  }

  FaviconLinkToTag = {

activestorage/test/template/image_tag_test.rb

@@ -11,17 +11,17 @@ class ActiveStorage::ImageTagTest < ActionView::TestCase
  end

  test "blob" do
    assert_dom_equal %(<img alt="Racecar" src="#{polymorphic_url @blob}" />), image_tag(@blob)
    assert_dom_equal %(<img src="#{polymorphic_url @blob}" />), image_tag(@blob)
  end

  test "variant" do
    variant = @blob.variant(resize: "100x100")
    assert_dom_equal %(<img alt="Racecar" src="#{polymorphic_url variant}" />), image_tag(variant)
    assert_dom_equal %(<img src="#{polymorphic_url variant}" />), image_tag(variant)
  end

  test "attachment" do
    attachment = ActiveStorage::Attachment.new(blob: @blob)
    assert_dom_equal %(<img alt="Racecar" src="#{polymorphic_url attachment}" />), image_tag(attachment)
    assert_dom_equal %(<img src="#{polymorphic_url attachment}" />), image_tag(attachment)
  end

  test "error when attachment's empty" do

guides/source/action_view_overview.md

@@ -414,7 +414,7 @@ By default, Rails links to these assets on the current host in the public folder

```ruby
config.action_controller.asset_host = "assets.example.com"
image_tag("rails.png") # => <img src="http://assets.example.com/images/rails.png" alt="Rails" />
image_tag("rails.png") # => <img src="http://assets.example.com/images/rails.png" />
```

#### auto_discovery_link_tag
@@ -453,7 +453,7 @@ image_url("edit.png") # => http://www.example.com/assets/edit.png
Returns an HTML image tag for the source. The source can be a full path or a file that exists in your `app/assets/images` directory.

```ruby
image_tag("icon.png") # => <img src="/assets/icon.png" alt="Icon" />
image_tag("icon.png") # => <img src="/assets/icon.png" />
```

#### javascript_include_tag

guides/source/api_documentation_guidelines.md

@@ -350,7 +350,7 @@ into account, one such example is

```ruby
# image_tag("icon.png")
#   # => <img alt="Icon" src="/assets/icon.png" />
#   # => <img src="/assets/icon.png" />
```

Although the default behavior for `#image_tag` is to always return