[Serialization] Lazily Resolve the Eraser Type of @ _typeEraser #30800
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CodaFi
commented
Apr 3, 2020
Type erasure requires a circular construction by its very nature:
@_typeEraser(AnyProto)
protocol Proto { /**/ }
public struct AnyProto : Proto {}
If we eagerly resolve AnyProto, the chain of resolution steps that
deserialization must make goes a little something like this:
Lookup(Proto)
-> Deserialize(@_typeEraser(AnyProto))
-> Lookup(AnyProto)
-> DeserializeInheritedStuff(AnyProto)
-> Lookup(Proto)
This cycle could be broken if the order of incremental inputs was
such that we had already cached the lookup of Proto.
Resolve this cycle in any case by suspending the deserialization of the
type eraser until the point it's demanded by adding
ResolveTypeEraserTypeRequest.
rdar://61270195
ModuleDecl is its own declaration context.
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Going through sil-opt is going to print the contents of the module without forcing the attribute which renders the test toothless. Now that we have the multifile test, we're testing it can be round-tripped through serialization anyhow.
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Type erasure requires a circular construction by its very nature:
If we eagerly resolve AnyProto, the chain of resolution steps that
deserialization must make goes a little something like this:
Now, this cycle could be broken if the order of incremental inputs was
such that we had already cached the lookup of Proto.
Resolve this cycle in any case by suspending the deserialization of the
type eraser until the point it's demanded by adding
ResolveTypeEraserTypeRequest.
rdar://61270195