[4.0] KeyPath: Fix out-of-bounds access when instantiating keypaths with optional chaining components. #12775
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…tional chaining components. When we pre-scan the components of a key path pattern to determine its runtime type and instance size, we would short-circuit upon seeing an optional-chaining component, since that makes a key path definitely read-only, but the loop also accumulates the size of the instance we're supposed to allocate, so…bad stuff happened. Leave out the short-circuit, fixing SR-6096 | rdar://problem/34889333 .
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@slavapestov Mind reviewing this for the 4.0 branch? |
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@swift-ci Please test |
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Explanation: Fixes an out-of-bounds access when using optional-chaining key paths in generic contexts or with index elements.
Scope: Fixes a runtime crash that many users have been running into.
Issue: SR-6096 | rdar://problem/35367114
Risk: Low
Testing: Swift CI, test case from Jira