Pavel Yaskevich c278717887 [CSSimplify] Avoid simplifying dependent members until pack expansions in the based are bound ...

Dependent members cannot be simplified if base type contains unresolved
pack expansion type variables because they don't give enough information
to substitution logic to form a correct type. For example:

```
protocol P { associatedtype V }
struct S<each T> : P { typealias V = (repeat (each T)?) }
```

If pack expansion is represented as `$T1` and its pattern is `$T2`, a
reference to `V` would get a type `S<Pack{$T}>.V` and simplified version
would be `Optional<Pack{$T1}>` instead of `Pack{repeat Optional<$T2>}`
because `$T1` is treated as a substitution for `each T` until bound.

Resolves: rdar://161207705

2025-10-07 00:20:51 -07:00

644 KiB

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