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[CS] Limit the number of chained @dynamicMemberLookup lookups

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Set an upper bound on the number of chained lookups we attempt to
avoid spinning while trying to recursively apply the same dynamic
member lookup to itself.

rdar://157288911
This commit is contained in:
Hamish Knight
2025-07-31 18:49:45 +01:00
parent 1f4cca6f4d
commit fb7f2d0ff2
15 changed files with 156 additions and 23 deletions
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30
test/attr/attr_dynamic_member_lookup.swift
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@@ -978,3 +978,33 @@ struct WithSendable {
get { false }
}
}
// Make sure we enforce a limit on the number of chained dynamic member lookups.
@dynamicMemberLookup
struct SelfRecursiveLookup<T> {
init(_: () -> T) {}
init(_: () -> KeyPath<Self, T>) {}
subscript<U>(dynamicMember kp: KeyPath<T, U>) -> SelfRecursiveLookup<U> {}
}
let selfRecurse1 = SelfRecursiveLookup { selfRecurse1.e }
// expected-error@-1 {{could not find member 'e'; exceeded the maximum number of nested dynamic member lookups}}
let selfRecurse2 = SelfRecursiveLookup { selfRecurse2[a: 0] }
// expected-error@-1 {{could not find member 'subscript'; exceeded the maximum number of nested dynamic member lookups}}
let selfRecurse3 = SelfRecursiveLookup { \.e }
// expected-error@-1 {{could not find member 'e'; exceeded the maximum number of nested dynamic member lookups}}
let selfRecurse4 = SelfRecursiveLookup { \.[a: 0] }
// expected-error@-1 {{could not find member 'subscript'; exceeded the maximum number of nested dynamic member lookups}}
extension SelfRecursiveLookup where T == SelfRecursiveLookup<SelfRecursiveLookup<SelfRecursiveLookup<Int>>> {
var terminator: T { fatalError() }
subscript(terminator terminator: Int) -> T { fatalError() }
}
let selfRecurse5 = SelfRecursiveLookup { selfRecurse5.terminator }
let selfRecurse6 = SelfRecursiveLookup { selfRecurse6[terminator: 0] }
let selfRecurse7 = SelfRecursiveLookup { \.terminator }
let selfRecurse8 = SelfRecursiveLookup { \.[terminator: 0] }