Add -eval-before-fork option to aid in debugging

Author: ajbouh

src/qa/cmd/run/run.go

@@ -73,6 +73,7 @@ func Main(env *cmd.Env, args []string) error {
 
 	errorsCaptureLocals := flags.String("errors-capture-locals", "false", "Use runtime debug API to capture locals from stack when raising errors")
 	captureStandardFds := flags.Bool("capture-standard-fds", true, "Capture stdout and stderr")
+	evalBeforeFork := flags.String("eval-before-fork", "", "Execute the given code before forking any workers or loading any files")
 	evalAfterFork := flags.String("eval-after-fork", "", "Execute the given code after a work forks, but before work begins")
 	sampleStack := flags.Bool("sample-stack", false, "Enable stack sampling")
 
@@ -329,6 +330,7 @@ func Main(env *cmd.Env, args []string) error {
 			"warmup":              *warmup,
 			"errorsCaptureLocals": *errorsCaptureLocals,
 			"captureStandardFds":  *captureStandardFds,
+			"evalBeforeFork":      *evalBeforeFork,
 			"evalAfterFork":       *evalAfterFork,
 			"sampleStack":         *sampleStack,
 		}

src/qa/runner-assets/ruby/shared.rb

@@ -1225,6 +1225,9 @@ def main(args)
     end
     qa_trace.start
 
+    eval_before_fork = (passthrough['evalBeforeFork'] || '')
+    eval(eval_before_fork) unless eval_before_fork.empty?
+
     # Delegate prefork actions.
     @prefork.call(initial_files)