Avoid empty-hash merges on request hot paths

CHANGELOG.md

@@ -10,6 +10,7 @@
 * [#2684](https://github.com/ruby-grape/grape/pull/2684): Readability refactors: case/when, guard clauses, small cleanups - [@ericproulx](https://github.com/ericproulx).
 * [#2687](https://github.com/ruby-grape/grape/pull/2687): Skip backtrace capture on internal validation exceptions - [@ericproulx](https://github.com/ericproulx).
 * [#2688](https://github.com/ruby-grape/grape/pull/2688): Consolidate user-registered rescue handler lookup into `Middleware::Error#registered_rescue_handler` backed by a shared `rescue_handler_from` primitive - [@ericproulx](https://github.com/ericproulx).
+* [#2689](https://github.com/ruby-grape/grape/pull/2689): Avoid empty-hash merges on request hot paths - [@ericproulx](https://github.com/ericproulx).
 * Your contribution here.
 
 #### Fixes

UPGRADING.md

@@ -3,6 +3,10 @@ Upgrading Grape
 
 ### Upgrading to >= 3.3
 
+#### `Grape::Request#grape_routing_args` has been removed
+
+`grape_routing_args` was previously public to support third-party `params_builder` extensions, which have since been removed. With no remaining callers, the method has been removed. If you were calling it externally, read `env[Grape::Env::GRAPE_ROUTING_ARGS]` directly.
+
 #### `endpoint_run_filters.grape` notification no longer fired for empty filter lists
 
 `ActiveSupport::Notifications` subscribers listening to `endpoint_run_filters.grape` will no longer receive an event when the filter list for a given phase (`:before`, `:before_validation`, `:after_validation`, `:after`, `:finally`) is empty. Previously every phase emitted an event on every request regardless of whether any filters were registered. If you relied on these events to infer per-phase timing, subscribe to `endpoint_run.grape` (which always fires once per request) or register a no-op filter to keep the phase instrumented.

lib/grape/dsl/entity.rb

@@ -32,7 +32,7 @@ def present(*args, root: nil, with: nil, **options)
         representation = { root => representation } if root
 
         if key
-          representation = (body || {}).merge(key => representation)
+          representation = body&.merge(key => representation) || { key => representation }
         elsif entity_class.present? && body
           raise ArgumentError, "Representation of type #{representation.class} cannot be merged." unless representation.respond_to?(:merge)
 

lib/grape/request.rb

@@ -156,16 +156,12 @@ def cookies
       @cookies ||= Grape::Cookies.new(-> { rack_cookies })
     end
 
-    # needs to be public until extensions param_builder are removed
-    def grape_routing_args
-      # preserve version from query string parameters
-      env[Grape::Env::GRAPE_ROUTING_ARGS]&.except(:version, :route_info) || {}
-    end
-
     private
 
     def make_params
-      @params_builder.call(rack_params).deep_merge!(grape_routing_args)
+      params = @params_builder.call(rack_params)
+      routing_args = env[Grape::Env::GRAPE_ROUTING_ARGS]&.except(:version, :route_info)&.presence
+      routing_args ? params.deep_merge!(routing_args) : params
     rescue *Grape::RACK_ERRORS
       raise Grape::Exceptions::RequestError
     end

lib/grape/router.rb

@@ -137,8 +137,7 @@ def transaction(input, method, env)
     def process_route(route, input, env, include_allow_header: false)
       args = env[Grape::Env::GRAPE_ROUTING_ARGS] || { route_info: route }
       route_params = route.params(input)
-      routing_args = args.merge(route_params || {})
-      env[Grape::Env::GRAPE_ROUTING_ARGS] = routing_args
+      env[Grape::Env::GRAPE_ROUTING_ARGS] = route_params.blank? ? args : args.merge(route_params)
       env[Grape::Env::GRAPE_ALLOWED_METHODS] = route.allow_header if include_allow_header
       route.call(env)
     end