Sema: Fix conditional downcasts from Swift types to CF types [4.0] #10063
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Conditional and forced downcasts enter a constraint that almost always succeeds; only when applying the solution do we evaluate the feasability of the cast and determine if it always succeeds, always fails, or conditionally succeeds. This changes how the resulting AST is represented and can also emit diagnostics. If the conditional cast is at this stage determined to always succeed, we treat it as an unconditional cast, going through ExprRewriter::coerceToType() to build the AST for the coercion. However conditional cast constraints don't enter the same restrictions into the solution as unconditional casts do, so coerceToType() would fall over if casting a Swift type to a CF type by first bridging the Swift type to Objective-C. Get around this by checking for this case explicitly when lowering a CoerceExpr. It feels like there's a more fundamental issue here with how casts are modeled in the constraint solver, but I'm not going to try understanding that now. Fixes <rdar://problem/32227571>.
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@swift-ci Please test |
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Description: Fixes a crash when applying a solution containing a conditional or forced cast from a Swift collection to the corresponding CF collection type.
Origination: The bug has always been there.
Risk: Low, the code path in question would have asserted otherwise.
Tested: New tests added.
Reviewed by: @DougGregor
Radar: rdar://problem/32227571