Use JSON to marshal errors from children

[woodruffw]

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This replaces our use of Marshal to send exceptions from child processes to their controlling parents with a JSON representation of the exception state. This JSON representation is then wrapped in a new exception class, ChildProcessError. For particularly interesting exceptions in child processes (namely BuildErrors), we reify the ChildProcessError back into its original exception (which keeps analytics and other parts of the codebase that use it directly happy).

[MikeMcQuaid]

Thanks @woodruffw!

[DomT4]

brew formula-analytics --days-ago=30 --json --build-error > _data/analytics/build-error/30d.json
Error: badRequest: Invalid JSON payload received. Unknown name "json_class" at 'report_requests[0].dimension_filter_clauses[0].filters[0].expressions[0]': Cannot find field.
Invalid JSON payload received. Unknown name "s" at 'report_requests[0].dimension_filter_clauses[0].filters[0].expressions[0]': Cannot find field.
Invalid JSON payload received. Unknown name "json_class" at 'report_requests[0].sampling_level': Cannot find field.
Invalid JSON payload received. Unknown name "s" at 'report_requests[0].sampling_level': Cannot find field.

Related?

[woodruffw]

Yeah, looks like it. Hmm, I thought I handled the cases where we need real BuildErrors and not just ChildProcessErrors, but maybe I missed one.