#220 - Throw a ProcessFailedException instead of a FatalError on the stop error strategy

[njoubert-cleverage]

Description

Fixes #220.

When a task fails with the stop error strategy (the default), the process manager throws a Symfony\Component\ErrorHandler\Error\FatalError. This has three consequences:

• The command exits with code 0 when a process fails: FatalError is an \Error, not an \Exception, and the console application does not turn it into a non-zero exit code. A cron job, a CI job or a supervisor cannot detect failures. An unknown process code, which throws an \Exception, exits with code 1.
• ProcessLauncherTask does not detect failed sub-processes: it relies on the sub-process exit code, so a sub-process failing in stop strategy is considered successful and the parent process ends with "executed successfully".
• The original exception is lost: only its message (and file/line) is copied, it is not attached as previous. Its class, code and trace are lost, and a catch (\Exception) around ProcessManager::execute() does not catch the failure.

This PR:

• Add a dedicated CleverAge\ProcessBundle\Exception\ProcessFailedException (a \RuntimeException implementing ProcessExceptionInterface), thrown instead of the FatalError, with the same message and the original exception as previous.
• As a consequence, the command exits with code 1 on failure, and ProcessLauncherTask detects failed sub-processes.
• Update the documentation (01-quick_start.md automation section, 04-advanced_workflow.md, 06-testing.md), add tests.

The new regression tests fail on main and pass with this fix. PHPUnit, PHPStan, PHP-CS-Fixer and Rector pass.

Requirements

• Documentation updates
  • Reference
  • Cookbooks
  • Changelog
• Unit tests

Breaking changes

Minor: the exception thrown on a stop failure is now a ProcessFailedException (\RuntimeException) instead of a FatalError (\Error). Code catching FatalError or \Error explicitly must catch ProcessFailedException instead (catch (\Throwable) keeps working). Scripts relying on the (wrong) exit code 0 of a failed process now get 1. symfony/error-handler is no longer used by src/ but is kept in composer.json.

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