persistent and retries plugin now work well together

When persistent and retries are loaded separately, the options won't be
just overwritten; instead, changes will be kept, and max_retries will be
the max value of what both plugins load (in case the user sets its own
option)

lib/httpx/plugins/persistent.rb

@@ -19,7 +19,12 @@ module HTTPX
     #
     module Persistent
       def self.load_dependencies(klass)
-        klass.plugin(:retries, max_retries: 1, retry_change_requests: true)
+        max_retries = if klass.default_options.respond_to?(:max_retries)
+          [klass.default_options.max_retries, 1].max
+        else
+          1
+        end
+        klass.plugin(:retries, max_retries: max_retries, retry_change_requests: true)
       end
 
       def self.extra_options(options)

lib/httpx/plugins/rate_limiter.rb

@@ -17,6 +17,7 @@ module HTTPX
 
         def load_dependencies(klass)
           klass.plugin(:retries,
+                       retry_change_requests: true,
                        retry_on: method(:retry_on_rate_limited_response),
                        retry_after: method(:retry_after_rate_limit))
         end

lib/httpx/session.rb

@@ -221,7 +221,7 @@ module HTTPX
       def plugin(pl, options = nil, &block)
         # raise Error, "Cannot add a plugin to a frozen config" if frozen?
         pl = Plugins.load_plugin(pl) if pl.is_a?(Symbol)
-        unless @plugins.include?(pl)
+        if !@plugins.include?(pl)
           @plugins << pl
           pl.load_dependencies(self, &block) if pl.respond_to?(:load_dependencies)
           @default_options = @default_options.dup
@@ -245,6 +245,13 @@ module HTTPX
           opts.connection_class.__send__(:include, pl::ConnectionMethods) if defined?(pl::ConnectionMethods)
           pl.configure(self, &block) if pl.respond_to?(:configure)
 
+          @default_options.freeze
+        elsif options
+          # this can happen when two plugins are loaded, an one of them calls the other under the hood,
+          # albeit changing some default.
+          @default_options = @default_options.dup
+          @default_options = @default_options.merge(options)
+
           @default_options.freeze
         end
         self

test/https_test.rb

@@ -26,6 +26,7 @@ class HTTPSTest < Minitest::Test
   include Plugins::Multipart
   include Plugins::Expect
   include Plugins::RateLimiter
+  include Plugins::Persistent unless RUBY_ENGINE == "jruby" || RUBY_VERSION < "2.3"
 
   def test_connection_coalescing
     coalesced_origin = "https://#{ENV["HTTPBIN_COALESCING_HOST"]}"

test/support/requests/plugins/persistent.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+module Requests
+  module Plugins
+    module Persistent
+      def test_persistent
+        uri = build_uri("/get")
+
+        non_persistent_session = HTTPX.plugin(SessionWithPool)
+        response = non_persistent_session.get(uri)
+        verify_status(response, 200)
+        assert non_persistent_session.pool.connections.empty?, "unexpected connections ()"
+
+        persistent_session = non_persistent_session.plugin(:persistent)
+        response = persistent_session.get(uri)
+        verify_status(response, 200)
+        assert persistent_session.pool.connections.size == 1, "unexpected connections ()"
+
+        persistent_session.close
+        assert persistent_session.pool.connections.empty?, "unexpected connections ()"
+      end
+
+      def test_persistent_options
+        retry_persistent_session = HTTPX.plugin(:persistent).plugin(:retries, max_retries: 4)
+        options = retry_persistent_session.send(:default_options)
+        assert options.max_retries == 4
+        assert options.retry_change_requests
+        assert options.persistent
+
+        persistent_retry_session = HTTPX.plugin(:retries, max_retries: 4).plugin(:persistent)
+        options = persistent_retry_session.send(:default_options)
+        assert options.max_retries == 4
+        assert options.retry_change_requests
+        assert options.persistent
+      end
+    end
+  end
+end