1 files changed, 167 insertions, 0 deletions
diff --git a/spec/initializers/enumerator_next_patch_spec.rb b/spec/initializers/enumerator_next_patch_spec.rb
new file mode 100644
index 00000000000..99e73af5e86
--- /dev/null
+++ b/spec/initializers/enumerator_next_patch_spec.rb
@@ -0,0 +1,167 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'Enumerator#next patch fix' do
+  describe 'Enumerator' do
+    RSpec::Matchers.define :contain_unique_method_calls_in_order do |expected|
+      attr_reader :actual
+
+      match do |actual|
+        @actual_err = actual
+        regexps = expected.map { |method_name| { name: method_name, regexp: make_regexp(method_name) } }
+        @actual = actual.backtrace.filter_map do |line|
+          regexp = regexps.find { |r| r[:regexp].match? line }
+
+          regexp[:name] if regexp
+        end
+
+        expected == @actual
+      end
+
+      diffable
+
+      failure_message do
+        "#{super()}\n\nFull error backtrace:\n  #{@actual_err.backtrace.join("\n  ")}"
+      end
+
+      private
+
+      def make_regexp(method_name)
+        Regexp.new("/spec/initializers/enumerator_next_patch_spec\\.rb:[0-9]+:in `#{method_name}'$")
+      end
+    end
+
+    def have_been_raised_by_next_and_not_fixed_up
+      contain_unique_method_calls_in_order %w(call_enum_method)
+    end
+
+    def have_been_raised_by_enum_object_and_fixed_up
+      contain_unique_method_calls_in_order %w(make_error call_enum_method)
+    end
+
+    def have_been_raised_by_nested_next_and_fixed_up
+      contain_unique_method_calls_in_order %w(call_nested_next call_enum_method)
+    end
+
+    methods = [
+      {
+        name: 'next',
+        expected_value: 'Test value'
+      },
+      {
+        name: 'next_values',
+        expected_value: ['Test value']
+      },
+      {
+        name: 'peek',
+        expected_value: 'Test value'
+      },
+      {
+        name: 'peek_values',
+        expected_value: ['Test value']
+      }
+    ]
+
+    methods.each do |method|
+      describe "##{method[:name]}" do
+        def call_enum_method
+          enumerator.send(method_name)
+        end
+
+        let(:method_name) { method[:name] }
+
+        subject { call_enum_method }
+
+        describe 'normal yield' do
+          let(:enumerator) { Enumerator.new { |yielder| yielder << 'Test value' } }
+
+          it 'returns yielded value' do
+            is_expected.to eq(method[:expected_value])
+          end
+        end
+
+        describe 'end of iteration' do
+          let(:enumerator) { Enumerator.new { |_| } }
+
+          it 'does not fix up StopIteration' do
+            expect { subject }.to raise_error do |err|
+              expect(err).to be_a(StopIteration)
+              expect(err).to have_been_raised_by_next_and_not_fixed_up
+            end
+          end
+
+          context 'nested enum object' do
+            def call_nested_next
+              nested_enumerator.next
+            end
+
+            let(:nested_enumerator) { Enumerator.new { |_| } }
+            let(:enumerator) { Enumerator.new { |yielder| yielder << call_nested_next } }
+
+            it 'fixes up StopIteration thrown by another instance of #next' do
+              expect { subject }.to raise_error do |err|
+                expect(err).to be_a(StopIteration)
+                expect(err).to have_been_raised_by_nested_next_and_fixed_up
+              end
+            end
+          end
+        end
+
+        describe 'arguments error' do
+          def call_enum_method
+            enumerator.send(method_name, 'extra argument')
+          end
+
+          let(:enumerator) { Enumerator.new { |_| } }
+
+          it 'does not fix up ArgumentError' do
+            expect { subject }.to raise_error do |err|
+              expect(err).to be_a(ArgumentError)
+              expect(err).to have_been_raised_by_next_and_not_fixed_up
+            end
+          end
+        end
+
+        describe 'error' do
+          let(:enumerator) { Enumerator.new { |_| raise error } }
+          let(:error) { make_error }
+
+          it 'fixes up StopIteration' do
+            def make_error
+              StopIteration.new.tap { |err| err.set_backtrace(caller) }
+            end
+
+            expect { subject }.to raise_error do |err|
+              expect(err).to be(error)
+              expect(err).to have_been_raised_by_enum_object_and_fixed_up
+            end
+          end
+
+          it 'fixes up ArgumentError' do
+            def make_error
+              ArgumentError.new.tap { |err| err.set_backtrace(caller) }
+            end
+
+            expect { subject }.to raise_error do |err|
+              expect(err).to be(error)
+              expect(err).to have_been_raised_by_enum_object_and_fixed_up
+            end
+          end
+
+          it 'adds backtrace from other errors' do
+            def make_error
+              StandardError.new('This is a test').tap { |err| err.set_backtrace(caller) }
+            end
+
+            expect { subject }.to raise_error do |err|
+              expect(err).to be(error)
+              expect(err).to have_been_raised_by_enum_object_and_fixed_up
+              expect(err.message).to eq('This is a test')
+            end
+          end
+        end
+      end
+    end
+  end
+end