Simplify Codable Synthesis #33392
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Simplify Codable Synthesis #33392
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validateCodingKeysEnum cannot iterate over a hashed collection without ordering guarantees.
This complexity is due to the implementation constraints of Codable synthesis at a time when the type checker could return partially-validated results. This is no longer the case, so all of this code is just technical debt.
The quad-state here is completely superfluous. Break it down into an enum class that encodes the relevant cases we care about and clean up its sole caller.
This more powerful primitive is capable of 1) Detecting invalid classes 2) Detecting invalid superclasses 3) Detecting circularity in inheritance hierarchies The attached crasher demonstrates the reason we need to validate all of these predicates. Simply put, a circular class hierarchy is always going to report the superclass conforms to any protocol with a declaration in the source. Leveraging this, one could construct any circular class hierarchy, and a conformance to Codable would immediately crash because we got as far as trying to build a CodingKeys enum with an absolutely nonsensical structure. This also has the added benefit of de-complecting an enormous amount of codable conformance code. rdar://66588925
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Ultimately, this patchset is to fix the crash reported in rdar://66588925. But, while I'm here, remove a ton of needless complexity from codable synthesis.