worker: raise exception instead of calling sys.exit() with child's code When a worker process returns an error code, we would call `sys.exit()` with that exit code on the main process. The `SystemExit` exception would then get caught in `scmutil.callcatch()`, which would return that error code. The comment there says "Commands shouldn't sys.exit directly", which I agree with. This patch changes it so we raise a specific exception when a worker fails so we can catch instead. I think that means that `SystemExit` is now always an internal error. (I had earlier thought that this call to `sys.exit()` was from within the child process until Matt Harbison made me look again, so thanks for that!) Differential Revision: https://phab.mercurial-scm.org/D9287

--- a/mercurial/error.py	Tue Nov 03 09:56:02 2020 -0800
+++ b/mercurial/error.py	Sat Nov 07 21:50:28 2020 -0800
@@ -130,6 +130,13 @@
     __bytes__ = _tobytes
 
 
+class WorkerError(Exception):
+    """Exception raised when a worker process dies."""
+
+    def __init__(self, status_code):
+        self.status_code = status_code
+
+
 class InterventionRequired(Hint, Exception):
     """Exception raised when a command requires human intervention."""