Support On-Demand Resource

CHANGELOG.md

@@ -3,7 +3,10 @@
 ## Master
 
 ##### Enhancements
-
+* Support On-Demand Resource   
+  [JunyiXie](https://github.com/JunyiXie)
+  [#issue_number](https://github.com/CocoaPods/Core/pull/622)
+
 * Add a post_integrate_hook API  
   [lucasmpaim](https://github.com/lucasmpaim)
   [#7432](https://github.com/CocoaPods/CocoaPods/issues/7432)

lib/cocoapods-core/specification/consumer.rb

@@ -110,6 +110,12 @@ def user_target_xcconfig
         merge_values(attr, value_for_attribute(:xcconfig), value_for_attribute(:user_target_xcconfig))
       end
 
+      # @return [Hash{String=>String}]]  hash where the keys are the names of
+      #         the on demand resource and the values are their relative file
+      #         patterns.
+      #
+      spec_attr_accessor :on_demand_resources
+
       # @return [Hash{String => String}] the Info.plist values for the current specification
       #
       spec_attr_accessor :info_plist
@@ -473,6 +479,24 @@ def _prepare_resource_bundles(value)
         result
       end
 
+      # Ensures that the file patterns of the on demand resources are contained in
+      # an array.
+      #
+      # @param  [String, Array, Hash] value.
+      #         The value of the attribute as specified by the user.
+      #
+      # @return [Hash] the resources.
+      #
+      def _prepare_on_demand_resources(value)
+        result = {}
+        if value
+          value.each do |key, patterns|
+            result[key] = [*patterns].compact
+          end
+        end
+        result
+      end
+
       #-----------------------------------------------------------------------#
     end
   end

lib/cocoapods-core/specification/dsl.rb

@@ -1303,6 +1303,26 @@ def dependency=(args)
 
       #------------------#
 
+      # @!method on_demand_resources=(on_demand_resources)
+      #
+      #   A list of on_demand_resource that should be copied into the target bundle.
+      #
+      #   @example
+      #
+      #   s.on_demand_resources = {
+      #       'Tag1' => ['file1.png', 'file2.png']
+      #   }
+      #   @param  [String, Array<String>] resources
+      #           The on_demand_resources shipped with the Pod.
+      #
+      attribute :on_demand_resources,
+                :types => [String, Array],
+                :container => Hash,
+                :file_patterns => true,
+                :singularize => true
+
+      #------------------#
+
       # @!method resource_bundles=(*resource_bundles)
       #
       #   This attribute allows to define the name and the file of the resource
@@ -1370,6 +1390,7 @@ def dependency=(args)
                 :file_patterns => true,
                 :singularize   => true
 
+
       #------------------#
 
       # @!method exclude_files=(exclude_files)

lib/cocoapods-core/specification/linter.rb

@@ -311,6 +311,11 @@ def _validate_weak_frameworks(frameworks)
           ' specified by its name')
         end
       end
+
+      # Performs validations related to the `on_demand_resources` attribute.
+      #
+      def _validate_on_demand_resources(on_demand_resource)
+      end
 
       # Performs validations related to the `libraries` attribute.
       #