Sema: Correct composition of property wrappers. #26326
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jckarter
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This reverts commit 5e08f7d.
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beccadax
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Jul 26, 2019
| // mutating-ness of either the getter or setter, since we need both to | ||
| // perform a writeback cycle. | ||
| case Mutating: | ||
| if (Setter == DoesntExist) { |
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Does this need a special case? If the setter is DoesntExist, std::max() will always end up returning DoesntExist, right?
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I suppose not. It seems worth calling this out as a specific rule, though.
Fixes rdar://problem/53407949 | SR-11138. Previously, we'd only look at the outermost property wrapper to decide whether the wrapped property's getter and setter were `mutating` (or exist at all). In reality, this requires considering the semantics of the composed accesses of each wrapper layer's `wrappedValue` property. Fixing this systematically addresses a number of issues: - As SR-11138 reported, composing a nonmutating-get-set wrapper ought to produce a composed wrapper that's nonmutating. - We would previously allow a property wrapper with a mutating getter to be nested inside one with only a getter, even though the resulting implementation was unsound (because there's no mutable context for the inner wrapper to execute its get on.) - Similarly, we would construct unsound setters in cases where the setter can't exist, such as when the nested wrapper isn't settable but the outer wrapper is.
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Fixes rdar://problem/53407949 | SR-11138. Previously, we'd only look at the outermost property wrapper to decide whether the wrapped property's getter and setter were
mutating(or exist at all). In reality, this requires considering the semantics of the composed accesses of each wrapper layer'swrappedValueproperty. Fixing this systematically addresses a number of issues:As SR-11138 reported, composing a nonmutating-get-set wrapper ought to produce a composed wrapper that's nonmutating.
We would previously allow a property wrapper with a mutating getter to be nested inside one with only a getter, even though the resulting implementation was unsound (because there's no mutable context for the inner wrapper to execute its get on.)
Similarly, we would construct unsound setters in cases where the setter can't exist, such as when the nested wrapper isn't settable but the outer wrapper is.