[#1719] Fix missing headers before error! call

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 * Your contribution here.
 * [#1864](https://github.com/ruby-grape/grape/pull/1864): Adds `finally` on the API - [@myxoh](https://github.com/myxoh).
+* [#1869](https://github.com/ruby-grape/grape/pull/1869): Fix issue with empty headers after `error!` method call - [@anaumov](https://github.com/anaumov).
 
 #### Fixes
 

README.md

@@ -1815,7 +1815,7 @@ You can set a response header with `header` inside an API.
 header 'X-Robots-Tag', 'noindex'
 ```
 
-When raising `error!`, pass additional headers as arguments.
+When raising `error!`, pass additional headers as arguments. Additional headers will be merged with headers set before `error!` call.
 
 ```ruby
 error! 'Unauthorized', 401, 'X-Error-Detail' => 'Invalid token.'
@@ -2155,6 +2155,12 @@ instead of a message.
 error!({ error: 'unexpected error', detail: 'missing widget' }, 500)
 ```
 
+You can set additional headers for the response. They will be merged with headers set before `error!` call.
+
+```ruby
+error!('Something went wrong', 500, 'X-Error-Detail' => 'Invalid token.')
+```
+
 You can present documented errors with a Grape entity using the the [grape-entity](https://github.com/ruby-grape/grape-entity) gem.
 
 ```ruby

UPGRADING.md

@@ -1,6 +1,38 @@
 Upgrading Grape
 ===============
 
+### Upgrading to >= 1.2.4
+
+#### Headers in `error!` call
+
+Headers in `error!` will be merged with `headers` hash. If any header need to be cleared on `error!` call, make sure to move it to the `after` block.
+
+```ruby
+class SampleApi < Grape::API
+  before do
+    header 'X-Before-Header', 'before_call'
+  end
+
+  get 'ping' do
+    header 'X-App-Header', 'on_call'
+    error! :pong, 400, 'X-Error-Details' => 'Invalid token'
+  end
+end
+```
+**Former behaviour**
+```ruby
+  response.headers['X-Before-Header'] # => nil
+  response.headers['X-App-Header'] # => nil
+  response.headers['X-Error-Details'] # => Invalid token
+```
+
+**Current behaviour**
+```ruby
+  response.headers['X-Before-Header'] # => 'before_call'
+  response.headers['X-App-Header'] # => 'on_call'
+  response.headers['X-Error-Details'] # => Invalid token
+```
+
 ### Upgrading to >= 1.2.1
 
 #### Obtaining the name of a mounted class

lib/grape/dsl/inside_route.rb

@@ -134,8 +134,10 @@ def version
       #
       # @param message [String] The message to display.
       # @param status [Integer] the HTTP Status Code. Defaults to default_error_status, 500 if not set.
-      def error!(message, status = nil, headers = nil)
+      # @param additional_headers [Hash] Addtional headers for the response.
+      def error!(message, status = nil, additional_headers = nil)
         self.status(status || namespace_inheritable(:default_error_status))
+        headers = additional_headers.present? ? header.merge(additional_headers) : header
         throw :error, message: message, status: self.status, headers: headers
       end
 

spec/grape/endpoint_spec.rb

@@ -1089,6 +1089,36 @@ def app
       expect(last_response.headers['X-Custom']).to eq('value')
     end
 
+    it 'merges additional headers with headers set before call' do
+      subject.before do
+        header 'X-Before-Test', 'before-sample'
+      end
+
+      subject.get '/hey' do
+        header 'X-Test', 'test-sample'
+        error!({ 'dude' => 'rad' }, 403, 'X-Error' => 'error')
+      end
+
+      get '/hey.json'
+      expect(last_response.headers['X-Before-Test']).to eq('before-sample')
+      expect(last_response.headers['X-Test']).to eq('test-sample')
+      expect(last_response.headers['X-Error']).to eq('error')
+    end
+
+    it 'does not merges additional headers with headers set after call' do
+      subject.after do
+        header 'X-After-Test', 'after-sample'
+      end
+
+      subject.get '/hey' do
+        error!({ 'dude' => 'rad' }, 403, 'X-Error' => 'error')
+      end
+
+      get '/hey.json'
+      expect(last_response.headers['X-Error']).to eq('error')
+      expect(last_response.headers['X-After-Test']).to be_nil
+    end
+
     it 'sets the status code for the endpoint' do
       memoized_endpoint = nil