Improve change mather detection of objects that have changed. (#1132)

* Add instance variables to changes detected

* Add benchmark for large objects

benchmarks/hashing_large_objects.rb

@@ -0,0 +1,50 @@
+require 'benchmark/ips'
+
+OBJECT_VARIABLES = Object.instance_method(:instance_variables)
+OBJECT_VARIABLE_GET = Object.instance_method(:instance_variable_get)
+
+def calculate_attribute_hashes(object)
+  OBJECT_VARIABLES.bind(object).call.map { |name| OBJECT_VARIABLE_GET.bind(object).call(name).hash }
+end
+
+[10, 100, 1000, 10000].each do |object_size|
+  klass = Class.new do
+    define_method(:initialize) do
+      object_size.times do |i|
+        instance_variable_set(:"@my_var_#{i}", 'a' * (rand * 100))
+      end
+    end
+  end
+  instance = klass.new
+
+  Benchmark.ips do |ips|
+    ips.report("Get hashes for object of size: #{instance.instance_variables.size}") do
+      calculate_attribute_hashes(instance)
+    end
+  end
+end
+
+# Warming up --------------------------------------
+# Get hashes for object of size: 10
+#                         14.412k i/100ms
+# Calculating -------------------------------------
+# Get hashes for object of size: 10
+#                         158.585k (± 5.2%) i/s -    792.660k in   5.012663s
+# Warming up --------------------------------------
+# Get hashes for object of size: 100
+#                          1.664k i/100ms
+# Calculating -------------------------------------
+# Get hashes for object of size: 100
+#                          17.041k (± 9.0%) i/s -     84.864k in   5.036735s
+# Warming up --------------------------------------
+# Get hashes for object of size: 1000
+#                        173.000  i/100ms
+# Calculating -------------------------------------
+# Get hashes for object of size: 1000
+#                           1.808k (± 4.6%) i/s -      9.169k in   5.082355s
+# Warming up --------------------------------------
+# Get hashes for object of size: 10000
+#                         16.000  i/100ms
+# Calculating -------------------------------------
+# Get hashes for object of size: 10000
+#                         176.298  (± 3.4%) i/s -    896.000  in   5.089070s

lib/rspec/matchers/built_in/change.rb

@@ -367,13 +367,16 @@ def value_representation
         def perform_change(event_proc)
           @actual_before = evaluate_value_proc
           @before_hash = @actual_before.hash
+          @before_attribute_hashes = calculate_attribute_hashes(@actual_before)
+
           yield @actual_before if block_given?
 
           return false unless Proc === event_proc
           event_proc.call
 
           @actual_after = evaluate_value_proc
           @actual_hash = @actual_after.hash
+          @after_attribute_hashes = calculate_attribute_hashes(@actual_after)
           true
         end
 
@@ -390,7 +393,9 @@ def changed?
           # possible for two values to be unequal (and of different classes)
           # but to return the same hash value. Also, some objects may change
           # their hash after being compared with `==`/`!=`.
-          @actual_before != @actual_after || @before_hash != @actual_hash
+          @actual_before != @actual_after ||
+          @before_hash != @actual_hash ||
+          @before_attribute_hashes != @after_attribute_hashes
         end
 
         def actual_delta
@@ -399,6 +404,14 @@ def actual_delta
 
       private
 
+        # methods are stashed to ensure we get access to variables on modified classes / BasicObject
+        OBJECT_VARIABLES = Object.instance_method(:instance_variables)
+        OBJECT_VARIABLE_GET = Object.instance_method(:instance_variable_get)
+
+        def calculate_attribute_hashes(object)
+          OBJECT_VARIABLES.bind(object).call.map { |name| OBJECT_VARIABLE_GET.bind(object).call(name).hash }
+        end
+
         def evaluate_value_proc
           @value_proc ? @value_proc.call : @receiver.__send__(@message)
         end

spec/rspec/matchers/built_in/change_spec.rb

@@ -368,6 +368,10 @@ def self.to_s
     expect { @instance.some_value = 6 }.to change { @instance.some_value }
   end
 
+  it "passes when actual has a value modified" do
+    expect { @instance.some_value = 6 }.to change { @instance }
+  end
+
   it "fails when actual is not modified by the block" do
     expect do
       expect {}.to change { @instance.some_value }