[CSBindings] Downgrade key path mutability based on contextual inform… #84491
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tshortli
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…ation
If key path literal is converted to a read-only type, let's not
use maximum mutability to avoid unnecessary conversions. This is
also important because accessor references are availability checked
and we need to avoid referencing something that is not actually
going to be used.
There are some edge-cases in this approach which would still
produce a conversions, i.e.:
```
struct S {
var a: Int
let b: Int
}
func test<T>(_: T, _: T) {}
test(\S.a, \S.b)
```
Here `\S.a` is going to be converted to `KeyPath<S, Int>`. Availability
checker would still have to recognize situations like that and skip
checking setters if they are not used.
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hamishknight
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@swift-ci please test |
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@swift-ci please test Windows platform |
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…king. Accessor availability diagnostics for key path expressions were first introduced by swiftlang#83931. Those changes were insufficient because sometimes key path expressions are generated in the AST with more mutability than is needed by the context and so setter availability could be diagnosed inappropriately. Key path expression binding was refined in swiftlang#84491 to make this less likely to occur. However, there are still some circumstances in which a mutable key path is generated in the AST and then immediately coerced into an immutable key path to satisfy the contextual type. This change infers the immutability of these key path expressions by looking through surrounding conversion expressions.
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@swift-ci please test Windows platform |
tshortli
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…king. Accessor availability diagnostics for key path expressions were first introduced by swiftlang#83931. Those changes were insufficient because sometimes key path expressions are generated in the AST with more mutability than is needed by the context and so setter availability could be diagnosed inappropriately. Key path expression binding was refined in swiftlang#84491 to make this less likely to occur. However, there are still some circumstances in which a mutable key path is generated in the AST and then immediately coerced into an immutable key path to satisfy the contextual type. This change infers the immutability of these key path expressions by looking through surrounding conversion expressions.
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…ation
If key path literal is converted to a read-only type, let's not use maximum mutability to avoid unnecessary conversions. This is also important because accessor references are availability checked and we need to avoid referencing something that is not actually going to be used.
There are some edge-cases in this approach which would still produce a conversions, i.e.:
Here
\S.ais going to be converted toKeyPath<S, Int>. Availability checker would still have to recognize situations like that and skip checking setters if they are not used.