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]

1 files changed, 9 insertions, 13 deletions

diff --git a/actionview/lib/action_view/helpers/asset_tag_helper.rb b/actionview/lib/action_view/helpers/asset_tag_helper.rb
index 82b0fcbf2e..4557c76dfe 100644
--- a/actionview/lib/action_view/helpers/asset_tag_helper.rb
+++ b/actionview/lib/action_view/helpers/asset_tag_helper.rb
@@ -13,7 +13,7 @@ module ActionView
     # 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 @@ module ActionView
       # 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 @@ module ActionView
       # 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 @@ module ActionView
         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 @@ module ActionView
       #   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