[5.7][CodeCompletion] Avoid creating circles in the USRBasedType supertype hierarchy #58636
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… hierarchy
You would think that superclass + conformances form a DAG. You are wrong!
We can achieve a circular supertype hierarcy with
```swift
protocol Proto : Class {}
class Class : Proto {}
```
USRBasedType is not set up for this. Serialization of code completion results from global modules can't handle cycles in the supertype hierarchy
because it writes the DAG leaf to root(s) and needs to know the type offsets. To get consistent results independent of where we start
constructing USRBasedTypes, ignore superclasses of protocols. If we kept track of already visited types, we would get different results depending on
whether we start constructing the USRBasedType hierarchy from Proto or Class.
Ignoring superclasses of protocols is safe to do because USRBasedType is an under-approximation anyway.
rdar://91765262
|
@swift-ci Please test |
airspeedswift
approved these changes
May 6, 2022
AnthonyLatsis
added
🍒 release cherry pick
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Cherry-pick #58522 to release/5.7
USRBasedType, which we use to model types for cached code completion results from other modules isn’t set up for this, it assumes that the supertype hierarchy forms a DAG (see main PR for more detail) and crashes with a stack overflow if an imported module contains such a circular type structure. To fix, ignore any superclass requirements on protocols, which eliminates the possibility of this super type circle.