Add workaround for rails infected error classes

Changelog.md

@@ -1,10 +1,22 @@
-# Unreleased
+# v0.10.27 2021-02-02
+
+* [#1216](https://github.com/mbj/mutant/pull/1216)
+
+  Fix exception serialization form rails infected code bases.
+  This case can happen when the killfork terminates abnormal,
+  and the resulting exception in the worker has to be propagated to
+  the main process for reporting.
+  On "normal" Ruby the exceptions are dump/loadable but rails and
+  its core extensions break this invariant. Hence mutant now
+  captures the essence of the exception in an attribute copy for
+  propagation.
 
 * [#1207](https://github.com/mbj/mutant/pull/1207)
 
   * Remove `#eql?` -> `#equal?` mutation
 
 * [#1210](https://github.com/mbj/mutant/pull/1210)
+
   * Remove generic mutation to `self`
 
 # v0.10.26 2021-01-16

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    mutant (0.10.26)
+    mutant (0.10.27)
       diff-lcs (~> 1.3)
       parser (~> 3.0.0)
       regexp_parser (~> 2.0, >= 2.0.3)

lib/mutant.rb

@@ -71,8 +71,9 @@ module Mutant
 require 'mutant/ast/meta/resbody'
 require 'mutant/parser'
 require 'mutant/isolation'
-require 'mutant/isolation/none'
+require 'mutant/isolation/exception'
 require 'mutant/isolation/fork'
+require 'mutant/isolation/none'
 require 'mutant/parallel'
 require 'mutant/parallel/driver'
 require 'mutant/parallel/source'

lib/mutant/isolation/exception.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module Mutant
+  # Module providing isolation
+  class Isolation
+    # Generic serializable exception data.
+    #
+    # This is required as our honored guests the Rails* ecosystem
+    # makes Marshal.dump on exceptions impossible.
+    #
+    # @see https://twitter.com/_m_b_j_/status/1356433184850907137
+    #
+    # for the full story and eventual reactions.
+    class Exception
+      include Anima.new(
+        :backtrace,
+        :message,
+        :original_class
+      )
+    end # Exception
+  end # Isolation
+end # Mutant

lib/mutant/isolation/fork.rb

@@ -133,7 +133,11 @@ def read_child_result
         def load_result(result_fragments)
           @value = world.marshal.load(result_fragments.join)
         rescue ArgumentError => exception
-          @exception = exception
+          @exception = Exception.new(
+            backtrace:      exception.backtrace,
+            message:        exception.message,
+            original_class: exception.class
+          )
         end
 
         # rubocop:disable Metrics/MethodLength

lib/mutant/reporter/cli/printer/isolation_result.rb

@@ -28,6 +28,7 @@ class IsolationResult < self
             ```
             %s
             %s
+            %s
             ```
           MESSAGE
 
@@ -81,7 +82,8 @@ def print_exception
 
             puts(
               EXCEPTION_ERROR_MESSAGE % [
-                exception.inspect,
+                exception.original_class,
+                exception.message,
                 exception.backtrace.join("\n")
               ]
             )

lib/mutant/version.rb

@@ -2,5 +2,5 @@
 
 module Mutant
   # Current mutant version
-  VERSION = '0.10.26'
+  VERSION = '0.10.27'
 end # Mutant

spec/unit/mutant/isolation/fork_spec.rb

@@ -500,7 +500,11 @@ def timer(now)
           expect(apply).to eql(
             described_class::Result.new(
               log:            log_fragment,
-              exception:      exception,
+              exception:      Mutant::Isolation::Exception.new(
+                backtrace:      exception.backtrace,
+                message:        exception.message,
+                original_class: exception.class
+              ),
               process_status: child_status_success,
               timeout:        nil,
               value:          nil

spec/unit/mutant/reporter/cli/printer/isolation_result_spec.rb

@@ -26,15 +26,11 @@
 
     context 'on exception isolation error' do
       let(:exception) do
-        Class.new(RuntimeError) do
-          def inspect
-            '<TestException>'
-          end
-
-          def backtrace
-            %w[first last]
-          end
-        end.new('foo')
+        Mutant::Isolation::Exception.new(
+          backtrace:      %w[first last],
+          message:        'Some Exception Message',
+          original_class: ArgumentError
+        )
       end
 
       it_reports <<~'STR'
@@ -51,7 +47,8 @@ def backtrace
         The following exception was raised while reading the killfork result:
 
         ```
-        <TestException>
+        ArgumentError
+        Some Exception Message
         first
         last
         ```