validates_nilness_of RSpec 3 non-deprecation

MSP-12130

metasploit-cache runs with deprecations as errors, so
validates_uniqueness_of needs to use the non-deprecated message methods
for RSpec 3 when they are available.

lib/metasploit/model/version.rb

@@ -7,7 +7,7 @@ module Version
       # The minor version number, scoped to the {MAJOR} version number.
       MINOR = 29
       # The patch number, scoped to the {MAJOR} and {MINOR} version numbers.
-      PATCH = 1
+      PATCH = 2
       # The prerelease version, scoped to the {MAJOR}, {MINOR}, and {PATCH} version numbers.
       PRERELEASE = 'validates-nilness-of'
 

spec/support/matchers/validate_nilness_of.rb

@@ -3,11 +3,25 @@
     "require nil for #{attribute}"
   end
 
-  failure_message_for_should do |instance|
+  failure_message_method = :failure_message_for_should
+
+  # RSpec compatibility without deprecation warnings
+  if respond_to?(:failure_message)
+    failure_message_method = :failure_message
+  end
+
+  send(failure_message_method) do |instance|
     "Expected errors to include 'must be nil' when #{attribute} is set to an arbitrary string"
   end
 
-  failure_message_for_should_not do |instance|
+  failure_message_when_negated_method = :failure_message_for_should_not
+
+  # RSpec compatibility without deprecation warnings
+  if respond_to?(:failure_message_when_negated)
+    failure_message_when_negated_method = :failure_message_when_negated
+  end
+
+  send(failure_message_when_negated_method) do |instance|
     "Expected errors not to include 'must be nil' when #{attribute} is set"
   end