Provide friendlier access to request variants

Closes #18933.

4 files changed, 90 insertions, 37 deletions

diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index 3f6cb5a5b1..e3e5787183 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -1,13 +1,27 @@
+*   Provide friendlier access to request variants.
+
+        request.variant = :phone
+        request.variant.phone?  # true
+        request.variant.tablet? # false
+
+        request.variant = [:phone, :tablet]
+        request.variant.phone?                  # true
+        request.variant.desktop?                # false
+        request.variant.any?(:phone, :desktop)  # true
+        request.variant.any?(:desktop, :watch)  # false
+
+    *George Claghorn*
+
 *   Fix handling of empty X_FORWARDED_HOST header in raw_host_with_port
 
-    Previously, an empty X_FORWARDED_HOST header would cause
-    Actiondispatch::Http:URL.raw_host_with_port to return nil, causing
-    Actiondispatch::Http:URL.host to raise a NoMethodError.
+        Previously, an empty X_FORWARDED_HOST header would cause
+        Actiondispatch::Http:URL.raw_host_with_port to return nil, causing
+        Actiondispatch::Http:URL.host to raise a NoMethodError.
 
-    *Adam Forsyth*
+        *Adam Forsyth*
 
 *   Drop request class from RouteSet constructor.
- 
+
     If you would like to use a custom request class, please subclass and implement
     the `request_class` method.
 
diff --git a/actionpack/lib/action_controller/metal/mime_responds.rb b/actionpack/lib/action_controller/metal/mime_responds.rb
index 7dae171215..fab1be3459 100644
--- a/actionpack/lib/action_controller/metal/mime_responds.rb
+++ b/actionpack/lib/action_controller/metal/mime_responds.rb
@@ -288,16 +288,17 @@ module ActionController #:nodoc:
         end
 
         def variant
-          if @variant.nil?
+          if @variant.empty?
             @variants[:none] || @variants[:any]
-          elsif (@variants.keys & @variant).any?
-            @variant.each do |v|
-              return @variants[v] if @variants.key?(v)
-            end
           else
-            @variants[:any]
+            @variants[variant_key]
           end
         end
+
+        private
+          def variant_key
+            @variant.find { |variant| @variants.key?(variant) } || :any
+          end
       end
     end
   end
diff --git a/actionpack/lib/action_dispatch/http/mime_negotiation.rb b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
index 53a98c5d0a..6544aff7d2 100644
--- a/actionpack/lib/action_dispatch/http/mime_negotiation.rb
+++ b/actionpack/lib/action_dispatch/http/mime_negotiation.rb
@@ -10,8 +10,6 @@ module ActionDispatch
         self.ignore_accept_header = false
       end
 
-      attr_reader :variant
-
       # The MIME type of the HTTP request, such as Mime::XML.
       #
       # For backward compatibility, the post \format is extracted from the
@@ -75,18 +73,22 @@ module ActionDispatch
 
       # Sets the \variant for template.
       def variant=(variant)
-        if variant.is_a?(Symbol)
-          @variant = [variant]
-        elsif variant.nil? || variant.is_a?(Array) && variant.any? && variant.all?{ |v| v.is_a?(Symbol) }
-          @variant = variant
+        variant = Array(variant)
+
+        if variant.all? { |v| v.is_a?(Symbol) }
+          @variant = VariantInquirer.new(variant)
         else
-          raise ArgumentError, "request.variant must be set to a Symbol or an Array of Symbols, not a #{variant.class}. " \
+          raise ArgumentError, "request.variant must be set to a Symbol or an Array of Symbols. " \
             "For security reasons, never directly set the variant to a user-provided value, " \
             "like params[:variant].to_sym. Check user-provided value against a whitelist first, " \
             "then set the variant: request.variant = :tablet if params[:variant] == 'tablet'"
         end
       end
 
+      def variant
+        @variant ||= VariantInquirer.new
+      end
+
       # Sets the \format by string extension, which can be used to force custom formats
       # that are not controlled by the extension.
       #
@@ -139,6 +141,31 @@ module ActionDispatch
         order.include?(Mime::ALL) ? format : nil
       end
 
+      class VariantInquirer # :nodoc:
+        delegate :each, :empty?, to: :@variants
+
+        def initialize(variants = [])
+          @variants = variants
+        end
+
+        def any?(*candidates)
+          (@variants & candidates).any?
+        end
+
+        def to_ary
+          @variants
+        end
+
+        private
+          def method_missing(name, *args)
+            if name[-1] == '?'
+              any? name[0..-2].to_sym
+            else
+              super
+            end
+          end
+      end
+
       protected
 
       BROWSER_LIKE_ACCEPTS = /,\s*\*\/\*|\*\/\*\s*,/
diff --git a/actionpack/test/dispatch/request_test.rb b/actionpack/test/dispatch/request_test.rb
index 61cc4dcd7e..ab492665c9 100644
--- a/actionpack/test/dispatch/request_test.rb
+++ b/actionpack/test/dispatch/request_test.rb
@@ -1128,35 +1128,46 @@ class RequestEtag < BaseRequestTest
 end
 
 class RequestVariant < BaseRequestTest
-  test "setting variant" do
-    request = stub_request
+  setup do
+    @request = stub_request
+  end
 
-    request.variant = :mobile
-    assert_equal [:mobile], request.variant
+  test 'setting variant to a symbol' do
+    @request.variant = :phone
 
-    request.variant = [:phone, :tablet]
-    assert_equal [:phone, :tablet], request.variant
+    assert @request.variant.phone?
+    assert_not @request.variant.tablet?
+    assert @request.variant.any?(:phone, :tablet)
+    assert_not @request.variant.any?(:tablet, :desktop)
+  end
 
-    assert_raise ArgumentError do
-      request.variant = [:phone, "tablet"]
-    end
+  test 'setting variant to an array of symbols' do
+    @request.variant = [:phone, :tablet]
 
-    assert_raise ArgumentError do
-      request.variant = "yolo"
-    end
+    assert @request.variant.phone?
+    assert @request.variant.tablet?
+    assert_not @request.variant.desktop?
+    assert @request.variant.any?(:tablet, :desktop)
+    assert_not @request.variant.any?(:desktop, :watch)
   end
 
-  test "reset variant" do
-    request = stub_request
+  test 'clearing variant' do
+    @request.variant = nil
 
-    request.variant = nil
-    assert_equal nil, request.variant
+    assert @request.variant.empty?
+    assert_not @request.variant.phone?
+    assert_not @request.variant.any?(:phone, :tablet)
   end
 
-  test "setting variant with non symbol value" do
-    request = stub_request
+  test 'setting variant to a non-symbol value' do
+    assert_raise ArgumentError do
+      @request.variant = 'phone'
+    end
+  end
+
+  test 'setting variant to an array containing a non-symbol value' do
     assert_raise ArgumentError do
-      request.variant = "mobile"
+      @request.variant = [:phone, 'tablet']
     end
   end
 end