allow custom env keys in an embedded hash

lib/faraday/options.rb

@@ -205,6 +205,22 @@ module Faraday
 
     def_delegators :request, :params_encoder
 
+    def [](key)
+      if in_member_set?(key)
+        super(key)
+      else
+        custom_members[key]
+      end
+    end
+
+    def []=(key, value)
+      if in_member_set?(key)
+        super(key, value)
+      else
+        custom_members[key] = value
+      end
+    end
+
     def success?
       SuccessfulStatuses.include?(status)
     end
@@ -225,5 +241,30 @@ module Faraday
     def parallel?
       !!parallel_manager
     end
+
+    def custom_members
+      @custom_members ||= {}
+    end
+
+    def in_member_set?(key)
+      member_set.include?(key.to_sym)
+    end
+
+    def member_set
+      @member_set ||= Set.new(members)
+    end
+
+    def inspect
+      attrs = [nil]
+      members.each do |mem|
+        if value = send(mem)
+          attrs << "@#{mem}=#{value.inspect}"
+        end
+      end
+      if !custom_members.empty?
+        attrs << "@custom=#{custom_members.inspect}"
+      end
+      %(#<#{self.class}#{attrs.join(" ")}>)
+    end
   end
 end

test/options_test.rb

@@ -143,5 +143,25 @@ class OptionsTest < Faraday::TestCase
     assert_equal 1, options.a
     assert_nil options.b
   end
-end
 
+  def test_env_access_member
+    e = Faraday::Env.new
+    assert_nil e.method
+    e.method = :get
+    assert_equal :get, e.method
+  end
+
+  def test_env_access_symbol_non_member
+    e = Faraday::Env.new
+    assert_nil e[:custom]
+    e[:custom] = :boom
+    assert_equal :boom, e[:custom]
+  end
+
+  def test_env_access_string_non_member
+    e = Faraday::Env.new
+    assert_nil e["custom"]
+    e["custom"] = :boom
+    assert_equal :boom, e["custom"]
+  end
+end