Split spec files to examples programmatically

Instead of shelling out to rspec, we now split spec files into
individual examples programmatically, using the RSpec Core API. This is
faster and more robust, since we avoid common shell shenanigans.

Closes #6

lib/rspecq/worker.rb

@@ -162,39 +162,32 @@ def try_publish_queue!(queue)
       puts "Published queue (size=#{queue.publish(jobs)})"
     end
 
+    # Split a list of spec files into their individual examples.
+    #
     # NOTE: RSpec has to load the files before we can split them as individual
     # examples. In case a file to be splitted fails to be loaded
     # (e.g. contains a syntax error), we return the files unchanged, thereby
     # falling back to scheduling them as whole files. Their errors will be
     # reported in the normal flow when they're eventually picked up by a worker.
     def files_to_example_ids(files)
-      cmd = "DISABLE_SPRING=1 bundle exec rspec --dry-run --format json #{files.join(' ')} 2>&1"
-      out = `#{cmd}`
-      cmd_result = $?
-
-      if !cmd_result.success?
-        rspec_output = begin
-                         JSON.parse(out)
-                       rescue JSON::ParserError
-                         out
-                       end
-
-        log_event(
-          "Failed to split slow files, falling back to regular scheduling",
-          "error",
-          rspec_output: rspec_output,
-          cmd_result: cmd_result.inspect,
-        )
+      out = StringIO.new
 
-        pp rspec_output
+      reset_rspec_state!
 
-        return files
-      end
-
-      JSON.parse(out)["examples"].map { |e| e["id"] }
+      RSpec.configuration.add_formatter(RSpec::Core::Formatters::JsonFormatter.new(out))
+      RSpec.configuration.files_or_directories_to_run = files_or_dirs_to_run
+      RSpec.configuration.dry_run = true
+
+      opts = RSpec::Core::ConfigurationOptions.new(files)
+      result = RSpec::Core::Runner.new(opts).run($stderr, $stdout)
+      return files if result != 0
+      JSON.parse(out.string)["examples"].map { |e| e["id"] }
+    ensure
+      RSpec.configuration.dry_run = false
+      # clear formatters
+      reset_rspec_state!
     end
 
-
     private
 
     def reset_rspec_state!

test/test_worker.rb

@@ -18,7 +18,7 @@ def test_files_to_example_ids
       ]
     )
 
-    assert_equal expected, actual
+    assert_equal expected.sort, actual.sort
   end
 
   def test_files_to_example_ids_failure_fallback
@@ -36,6 +36,6 @@ def test_files_to_example_ids_failure_fallback
         ]
       )
 
-    assert_equal expected, actual
+    assert_equal expected.sort, actual.sort
   end
 end