Moved join in call_with_allow_headers. Instead of being joined by def…

…ault it's joined when called

Replaced 'OPTIONS' by actual Grape::Http::Headers::OPTIONS.

CHANGELOG.md

@@ -5,7 +5,7 @@
 * Your contribution here.
 
 #### Fixes
-
+* [#1993](/~https://github.com/ruby-grape/grape/pull/1993): Lazy join allow header - [@ericproulx](/~https://github.com/ericproulx).
 * [#1987](/~https://github.com/ruby-grape/grape/pull/1987): Re-add exactly_one_of mutually exclusive error message - [@ZeroInputCtrl](/~https://github.com/ZeroInputCtrl).
 * [#1977](/~https://github.com/ruby-grape/grape/pull/1977): Skip validation for a file if it is optional and nil - [@dnesteryuk](/~https://github.com/dnesteryuk).
 * [#1976](/~https://github.com/ruby-grape/grape/pull/1976): Ensure classes/modules listed for autoload really exist - [@dnesteryuk](/~https://github.com/dnesteryuk).

lib/grape/api/instance.rb

@@ -227,7 +227,7 @@ def add_head_not_allowed_methods_and_options_methods
                 allowed_methods |= [Grape::Http::Headers::HEAD] if allowed_methods.include?(Grape::Http::Headers::GET)
               end
 
-              allow_header = (self.class.namespace_inheritable(:do_not_route_options) ? allowed_methods : [Grape::Http::Headers::OPTIONS] | allowed_methods).join(', ')
+              allow_header = (self.class.namespace_inheritable(:do_not_route_options) ? allowed_methods : [Grape::Http::Headers::OPTIONS] | allowed_methods)
 
               unless self.class.namespace_inheritable(:do_not_route_options) || allowed_methods.include?(Grape::Http::Headers::OPTIONS)
                 config[:endpoint].options[:options_route_enabled] = true

lib/grape/router.rb

@@ -106,7 +106,7 @@ def transaction(env)
         env,
         neighbor.allow_header,
         neighbor.endpoint
-      ) if neighbor && method == 'OPTIONS' && !cascade
+      ) if neighbor && method == Grape::Http::Headers::OPTIONS && !cascade
 
       route = match?(input, '*')
       return neighbor.endpoint.call(env) if neighbor && cascade && route
@@ -160,7 +160,7 @@ def greedy_match?(input)
     end
 
     def call_with_allow_headers(env, methods, endpoint)
-      env[Grape::Env::GRAPE_ALLOWED_METHODS] = methods
+      env[Grape::Env::GRAPE_ALLOWED_METHODS] = methods.join(', ')
       endpoint.call(env)
     end