🔧 Check type for config.responses_without_block

An `enum` type was added to Config::AttrTypeCoercion, to be used by
other future config options.

lib/net/imap/config.rb

@@ -115,7 +115,9 @@ def self.[](config) # :nodoc: unfinished API
       # | v0.4.13               | +:silence_deprecation_warning+ |
       # | v0.5                  | +:warn+                        |
       # | _eventually_          | +:raise+                       |
-      attr_accessor :responses_without_block
+      attr_accessor :responses_without_block, type: [
+        :silence_deprecation_warning, :warn, :raise,
+      ]
 
       # Creates a new config object and initialize its attribute with +attrs+.
       #

lib/net/imap/config/attr_type_coercion.rb

@@ -26,6 +26,7 @@ def self.attr_accessor(attr, type: nil)
           return unless type
           if    :boolean == type then boolean attr
           elsif Integer  == type then integer attr
+          elsif Array   === type then enum    attr, type
           else raise ArgumentError, "unknown type coercion %p" % [type]
           end
         end
@@ -39,6 +40,17 @@ def self.integer(attr)
           define_method :"#{attr}=" do |val| super Integer val end
         end
 
+        def self.enum(attr, enum)
+          enum = enum.dup.freeze
+          expected = -"one of #{enum.map(&:inspect).join(", ")}"
+          define_method :"#{attr}=" do |val|
+            unless enum.include?(val)
+              raise ArgumentError, "expected %s, got %p" % [expected, val]
+            end
+            super val
+          end
+        end
+
       end
     end
   end

test/net/imap/test_config.rb

@@ -50,6 +50,22 @@ class ConfigTest < Test::Unit::TestCase
     assert_equal 333, config.open_timeout
   end
 
+  test "enum type constraint" do
+    config = Config.new
+    config.responses_without_block = :silence_deprecation_warning
+    assert_equal :silence_deprecation_warning, config.responses_without_block
+    config.responses_without_block = :warn
+    assert_equal :warn, config.responses_without_block
+    config.responses_without_block = :raise
+    assert_equal :raise, config.responses_without_block
+    assert_raise(ArgumentError) do config.responses_without_block = false end
+    assert_equal :raise, config.responses_without_block
+    assert_raise(ArgumentError) do config.responses_without_block = 12345 end
+    assert_equal :raise, config.responses_without_block
+    assert_raise(ArgumentError) do config.responses_without_block = "warn" end
+    assert_equal :raise, config.responses_without_block
+  end
+
   test ".default" do
     default = Config.default
     assert default.equal?(Config.default)