Merge pull request #141 from waterlink/non_intrusive_contracts_v2

Refactor to contracts engine

Author: egonSchiele

TUTORIAL.md

@@ -510,12 +510,11 @@ This is because the first contract eliminated the possibility of `age` being les
 
 ## Contracts in modules
 
-To use contracts on module you need to include both `Contracts` and `Contracts::Modules` into it:
+Usage is the same as contracts in classes:
 
 ```ruby
 module M
   include Contracts
-  include Contracts::Modules
 
   Contract String => String
   def self.parse

lib/contracts.rb

@@ -1,12 +1,12 @@
 require "contracts/builtin_contracts"
 require "contracts/decorators"
-require "contracts/eigenclass"
 require "contracts/errors"
 require "contracts/formatters"
 require "contracts/invariants"
 require "contracts/method_reference"
-require "contracts/modules"
 require "contracts/support"
+require "contracts/engine"
+require "contracts/method_handler"
 
 module Contracts
   def self.included(base)
@@ -18,15 +18,13 @@ def self.extended(base)
   end
 
   def self.common(base)
-    Eigenclass.lift(base)
-
     return if base.respond_to?(:Contract)
 
     base.extend(MethodDecorators)
 
     base.instance_eval do
       def functype(funcname)
-        contracts = decorated_methods[:class_methods][funcname]
+        contracts = Engine.fetch_from(self).decorated_methods_for(:class_methods, funcname)
         if contracts.nil?
           "No contract for #{self}.#{funcname}"
         else
@@ -36,22 +34,14 @@ def functype(funcname)
     end
 
     base.class_eval do
-      unless base.instance_of?(Module)
-        def Contract(*args)
-          return if ENV["NO_CONTRACTS"]
-          if self.class == Module
-            puts %{
-Warning: You have added a Contract on a module function
-without including Contracts::Modules. Your Contract will
-just be ignored. Please include Contracts::Modules into
-your module.}
-          end
-          self.class.Contract(*args)
-        end
+      # TODO: deprecate
+      # Required when contracts are included in global scope
+      def Contract(*args)
+        self.class.Contract(*args)
       end
 
       def functype(funcname)
-        contracts = self.class.decorated_methods[:instance_methods][funcname]
+        contracts = Engine.fetch_from(self.class).decorated_methods_for(:instance_methods, funcname)
         if contracts.nil?
           "No contract for #{self.class}.#{funcname}"
         else

lib/contracts/decorators.rb

@@ -1,208 +1,18 @@
 module Contracts
   module MethodDecorators
     def self.extended(klass)
-      return if klass.respond_to?(:decorated_methods=)
-
-      class << klass
-        attr_accessor :decorated_methods
-      end
-    end
-
-    module EigenclassWithOwner
-      def self.lift(eigenclass)
-        fail Contracts::ContractsNotIncluded unless with_owner?(eigenclass)
-
-        eigenclass
-      end
-
-      private
-
-      def self.with_owner?(eigenclass)
-        eigenclass.respond_to?(:owner_class) && eigenclass.owner_class
-      end
+      Engine.apply(klass)
     end
 
-    # first, when you write a contract, the decorate method gets called which
-    # sets the @decorators variable. Then when the next method after the contract
-    # is defined, method_added is called and we look at the @decorators variable
-    # to find the decorator for that method. This is how we associate decorators
-    # with methods.
     def method_added(name)
-      common_method_added name, false
+      MethodHandler.new(name, false, self).handle
       super
     end
 
     def singleton_method_added(name)
-      common_method_added name, true
+      MethodHandler.new(name, true, self).handle
       super
     end
-
-    def pop_decorators
-      Array(@decorators).tap { @decorators = nil }
-    end
-
-    def fetch_decorators
-      pop_decorators + Eigenclass.lift(self).pop_decorators
-    end
-
-    def common_method_added(name, is_class_method)
-      decorators = fetch_decorators
-      return if decorators.empty?
-
-      @decorated_methods ||= { :class_methods => {}, :instance_methods => {} }
-
-      if is_class_method
-        method_reference = SingletonMethodReference.new(name, method(name))
-        method_type = :class_methods
-      else
-        method_reference = MethodReference.new(name, instance_method(name))
-        method_type = :instance_methods
-      end
-
-      @decorated_methods[method_type][name] ||= []
-
-      unless decorators.size == 1
-        fail %{
-Oops, it looks like method '#{name}' has multiple contracts:
-#{decorators.map { |x| x[1][0].inspect }.join("\n")}
-
-Did you accidentally put more than one contract on a single function, like so?
-
-Contract String => String
-Contract Num => String
-def foo x
-end
-
-If you did NOT, then you have probably discovered a bug in this library.
-Please file it along with the relevant code at:
-https://github.com/egonSchiele/contracts.ruby/issues
-        }
-      end
-
-      pattern_matching = false
-      decorators.each do |klass, args|
-        # a reference to the method gets passed into the contract here. This is good because
-        # we are going to redefine this method with a new name below...so this reference is
-        # now the *only* reference to the old method that exists.
-        # We assume here that the decorator (klass) responds to .new
-        decorator = klass.new(self, method_reference, *args)
-        new_args_contract = decorator.args_contracts
-        matched = @decorated_methods[method_type][name].select do |contract|
-          contract.args_contracts == new_args_contract
-        end
-        unless matched.empty?
-          fail ContractError.new(%{
-It looks like you are trying to use pattern-matching, but
-multiple definitions for function '#{name}' have the same
-contract for input parameters:
-
-#{(matched + [decorator]).map(&:to_s).join("\n")}
-
-Each definition needs to have a different contract for the parameters.
-          }, {})
-        end
-        @decorated_methods[method_type][name] << decorator
-        pattern_matching ||= decorator.pattern_match?
-      end
-
-      if @decorated_methods[method_type][name].any? { |x| x.method != method_reference }
-        @decorated_methods[method_type][name].each(&:pattern_match!)
-
-        pattern_matching = true
-      end
-
-      method_reference.make_alias(self)
-
-      return if ENV["NO_CONTRACTS"] && !pattern_matching
-
-      # in place of this method, we are going to define our own method. This method
-      # just calls the decorator passing in all args that were to be passed into the method.
-      # The decorator in turn has a reference to the actual method, so it can call it
-      # on its own, after doing it's decorating of course.
-
-      # Very important: THe line `current = #{self}` in the start is crucial.
-      # Not having it means that any method that used contracts could NOT use `super`
-      # (see this issue for example: https://github.com/egonSchiele/contracts.ruby/issues/27).
-      # Here's why: Suppose you have this code:
-      #
-      #     class Foo
-      #       Contract String
-      #       def to_s
-      #         "Foo"
-      #       end
-      #     end
-      #
-      #     class Bar < Foo
-      #       Contract String
-      #       def to_s
-      #         super + "Bar"
-      #       end
-      #     end
-      #
-      #     b = Bar.new
-      #     p b.to_s
-      #
-      #     `to_s` in Bar calls `super`. So you expect this to call `Foo`'s to_s. However,
-      #     we have overwritten the function (that's what this next defn is). So it gets a
-      #     reference to the function to call by looking at `decorated_methods`.
-      #
-      #     Now, this line used to read something like:
-      #
-      #       current = self#{is_class_method ? "" : ".class"}
-      #
-      #     In that case, `self` would always be `Bar`, regardless of whether you were calling
-      #     Foo's to_s or Bar's to_s. So you would keep getting Bar's decorated_methods, which
-      #     means you would always call Bar's to_s...infinite recursion! Instead, you want to
-      #     call Foo's version of decorated_methods. So the line needs to be `current = #{self}`.
-
-      current = self
-      method_reference.make_definition(self) do |*args, &blk|
-        ancestors = current.ancestors
-        ancestors.shift # first one is just the class itself
-        while current && !current.respond_to?(:decorated_methods) || current.decorated_methods.nil?
-          current = ancestors.shift
-        end
-        if !current.respond_to?(:decorated_methods) || current.decorated_methods.nil?
-          fail "Couldn't find decorator for method " + self.class.name + ":#{name}.\nDoes this method look correct to you? If you are using contracts from rspec, rspec wraps classes in it's own class.\nLook at the specs for contracts.ruby as an example of how to write contracts in this case."
-        end
-        methods = current.decorated_methods[method_type][name]
-
-        # this adds support for overloading methods. Here we go through each method and call it with the arguments.
-        # If we get a ContractError, we move to the next function. Otherwise we return the result.
-        # If we run out of functions, we raise the last ContractError.
-        success = false
-        i = 0
-        result = nil
-        expected_error = methods[0].failure_exception
-        until success
-          method = methods[i]
-          i += 1
-          begin
-            success = true
-            result = method.call_with(self, *args, &blk)
-          rescue expected_error => error
-            success = false
-            unless methods[i]
-              begin
-                ::Contract.failure_callback(error.data, false)
-              rescue expected_error => final_error
-                raise final_error.to_contract_error
-              end
-            end
-          end
-        end
-        result
-      end
-    end
-
-    def decorate(klass, *args)
-      if Support.eigenclass? self
-        return EigenclassWithOwner.lift(self).owner_class.decorate(klass, *args)
-      end
-
-      @decorators ||= []
-      @decorators << [klass, args]
-    end
   end
 
   class Decorator
@@ -220,7 +30,7 @@ def self.inherited(klass)
       # inside, `decorate` is called with those params.
       MethodDecorators.module_eval <<-ruby_eval, __FILE__, __LINE__ + 1
         def #{klass}(*args, &blk)
-          decorate(#{klass}, *args, &blk)
+          ::Contracts::Engine.fetch_from(self).decorate(#{klass}, *args, &blk)
         end
       ruby_eval
     end

lib/contracts/eigenclass.rb

@@ -0,0 +1,26 @@
+require "contracts/engine/base"
+require "contracts/engine/target"
+require "contracts/engine/eigenclass"
+
+require "forwardable"
+
+module Contracts
+  # Engine facade, normally you shouldn't refer internals of Engine
+  # module directly.
+  module Engine
+    class << self
+      extend Forwardable
+
+      # .apply(klass)      - enables contracts engine on klass
+      # .applied?(klass)   - returns true if klass has contracts engine
+      # .fetch_from(klass) - returns contracts engine for klass
+      def_delegators :base_engine, :apply, :applied?, :fetch_from
+
+      private
+
+      def base_engine
+        Base
+      end
+    end
+  end
+end