Fix maybe proc

lib/contracts.rb

@@ -113,8 +113,9 @@ def initialize(klass, method, *contracts)
     # == @has_proc_contract
     last_contract = args_contracts.last
     is_a_proc = last_contract.is_a?(Class) && (last_contract <= Proc || last_contract <= Method)
+    maybe_a_proc = last_contract.is_a?(Contracts::Maybe) && last_contract.include_proc?
 
-    @has_proc_contract = is_a_proc || last_contract.is_a?(Contracts::Func)
+    @has_proc_contract = is_a_proc || maybe_a_proc || last_contract.is_a?(Contracts::Func)
     # ====
 
     # == @has_options_contract

lib/contracts/builtin_contracts.rb

@@ -352,6 +352,10 @@ class Maybe < Or
     def initialize(*vals)
       super(*(vals + [nil]))
     end
+
+    def include_proc?
+      @vals.include? Proc
+    end
   end
 
   # Used to define contracts on functions passed in as arguments.

spec/contracts_spec.rb

@@ -404,6 +404,26 @@ def self.greeting(name)
         @o.double_with_proc(4)
       end.to raise_error(ContractError, /Actual: nil/)
     end
+
+    it "should succeed for maybe proc with no proc" do
+      expect do
+        @o.maybe_call(5)
+      end.to_not raise_error
+    end
+
+    it "should succeed for maybe proc with proc" do
+      expect do
+        @o.maybe_call(5) do
+          2 + 2
+        end
+      end.to_not raise_error
+    end
+
+    it "should fail for maybe proc with invalid input" do
+      expect do
+        @o.maybe_call("bad")
+      end.to raise_error(ContractError)
+    end
   end
 
   describe "varargs" do

spec/fixtures/fixtures.rb

@@ -120,8 +120,13 @@ def nested_array_complex_contracts(data)
   end
 
   Contract Proc => Any
-  def do_call(&blk)
-    blk.call
+  def do_call(&block)
+    block.call
+  end
+
+  Contract Args[Num], Maybe[Proc] => Any
+  def maybe_call(*vals, &block)
+    block.call if block
   end
 
   Contract Args[Num] => Num