Add support for procs in default value

lib/grape-swagger/doc_methods/parse_params.rb

@@ -52,7 +52,9 @@ def document_range_values(settings)
         end
 
         def document_default_value(settings)
-          @parsed_param[:default] = settings[:default] if settings.key?(:default)
+          return unless settings.key?(:default)
+
+          @parsed_param[:default] = settings[:default].is_a?(Proc) ? settings[:default].call : settings[:default]
         end
 
         def document_type_and_format(settings, data_type)

spec/swagger_v2/params_default_spec.rb

@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'Default param' do
+  def app
+    Class.new(Grape::API) do
+      format :json
+
+      desc 'Get with default proc value'
+      params do
+        optional :timestamp, type: String, default: proc { Time.now.utc.iso8601 },
+                             desc: 'A timestamp with default value from proc'
+        optional :static_value, type: String, default: 'static',
+                                desc: 'A parameter with static default value'
+      end
+      get '/with_default_proc' do
+        { timestamp: params[:timestamp], static_value: params[:static_value] }
+      end
+
+      add_swagger_documentation
+    end
+  end
+
+  describe 'swagger documentation' do
+    subject do
+      get '/swagger_doc'
+      JSON.parse(last_response.body)
+    end
+
+    it 'resolves the proc to a value for default parameter' do
+      parameters = subject['paths']['/with_default_proc']['get']['parameters']
+
+      timestamp_param = parameters.find { |p| p['name'] == 'timestamp' }
+      expect(timestamp_param).to be_present
+      expect(timestamp_param['default']).to be_present
+      # The default value should be a string in ISO8601 format
+      expect(timestamp_param['default']).to match(/\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z/)
+    end
+
+    it 'correctly documents static default values' do
+      parameters = subject['paths']['/with_default_proc']['get']['parameters']
+
+      static_param = parameters.find { |p| p['name'] == 'static_value' }
+      expect(static_param).to be_present
+      expect(static_param['default']).to eq('static')
+    end
+  end
+end