Merge pull request #265 from undees/undees/73-avoid-infinite-loop-on-mocked-is-a

Avoid infinite loop when classes mock #is_a?

Author: JonRowe

rspec-mocks/Changelog.md

@@ -1,6 +1,10 @@
 ### Development
 [Full Changelog](https://github.com/rspec/rspec/compare/rspec-mocks-v3.13.5...3-13-maintenance)
 
+Bug Fixes:
+
+* Work around possible infinite loop when stubbing `is_a?`. (Erin Paget, rspec/rspec#265)
+
 ### 3.13.5 / 2025-05-27
 [Full Changelog](https://github.com/rspec/rspec/compare/rspec-mocks-v3.13.4...rspec-mocks-v3.13.5)
 

rspec-mocks/lib/rspec/mocks/proxy.rb

@@ -32,7 +32,7 @@ def initialize(object, order_group, options={})
 
       # @private
       def ensure_can_be_proxied!(object)
-        return unless object.is_a?(Symbol)
+        return unless Symbol === object
 
         msg = "Cannot proxy frozen objects. Symbols such as #{object} cannot be mocked or stubbed."
         raise ArgumentError, msg

rspec-mocks/spec/rspec/mocks/matchers/receive_spec.rb

@@ -411,6 +411,56 @@ def receiver.method_missing(*); end # a poor man's stub...
         # rubocop:enable Lint/StructNewOverride
       end
 
+      shared_examples "handles stubbed #is_a? cleanly for a single instance" do
+        let(:klass) do
+          Class.new do
+            def call_stubbed_method
+              is_a?(self.class)
+            end
+          end
+        end
+
+        let(:object) { klass.new }
+
+        it "safely checks that the instance can be proxied" do
+          stubbed_answer = double("stubbed on an instance")
+          target.to receive(:is_a?).and_return(stubbed_answer)
+          expect(object.call_stubbed_method).to eq(stubbed_answer)
+        end
+      end
+
+      shared_examples "handles stubbed #is_a? cleanly for any_instance_of" do
+        let(:superclass) { Class.new }
+
+        let(:klass) do
+          Class.new(superclass) do
+            def call_stubbed_method
+              is_a?(self.class)
+            end
+          end
+        end
+
+        context "the class under test" do
+          let(:stubbed_class) { klass }
+
+          it "safely checks that the instance can be proxied" do
+            stubbed_answer = double("stubbed on the class under test")
+            target.to receive(:is_a?).and_return(stubbed_answer)
+            expect(klass.new.call_stubbed_method).to eq(stubbed_answer)
+          end
+        end
+
+        context "the parent of the class under test" do
+          let(:stubbed_class) { superclass }
+
+          it "safely checks that the instance can be proxied" do
+            stubbed_answer = double("stubbed on the superclass")
+            target.to receive(:is_a?).and_return(stubbed_answer)
+            expect(klass.new.call_stubbed_method).to eq(stubbed_answer)
+          end
+        end
+      end
+
       describe "allow(...).to receive" do
         it_behaves_like "an expect syntax allowance" do
           let(:receiver) { double }
@@ -422,6 +472,9 @@ def receiver.method_missing(*); end # a poor man's stub...
         it_behaves_like "handles frozen objects cleanly" do
           let(:target) { allow(object) }
         end
+        it_behaves_like "handles stubbed #is_a? cleanly for a single instance" do
+          let(:target) { allow(object) }
+        end
 
         context 'ordered with receive counts' do
           specify 'is not supported' do
@@ -486,6 +539,10 @@ def receiver.method_missing(*); end # a poor man's stub...
         it_behaves_like "resets partial mocks of any instance cleanly" do
           let(:target) { allow_any_instance_of(klass) }
         end
+
+        it_behaves_like "handles stubbed #is_a? cleanly for any_instance_of" do
+          let(:target) { allow_any_instance_of(stubbed_class) }
+        end
       end
 
       describe "allow_any_instance_of(...).not_to receive" do
@@ -532,6 +589,9 @@ def receiver.method_missing(*); end # a poor man's stub...
         it_behaves_like "handles frozen objects cleanly" do
           let(:target) { expect(object) }
         end
+        it_behaves_like "handles stubbed #is_a? cleanly for a single instance" do
+          let(:target) { allow(object) }
+        end
 
         context "ordered with receive counts" do
           let(:dbl) { double(:one => 1, :two => 2) }
@@ -631,6 +691,9 @@ def receiver.method_missing(*); end # a poor man's stub...
         it_behaves_like "resets partial mocks of any instance cleanly" do
           let(:target) { expect_any_instance_of(klass) }
         end
+        it_behaves_like "handles stubbed #is_a? cleanly for any_instance_of" do
+          let(:target) { expect_any_instance_of(stubbed_class) }
+        end
       end
 
       describe "expect(...).not_to receive" do