[5.7][stdlib] Work around binary compatibility issues with String index validation fixes in 5.7 #58993
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…lidation fixes in 5.7 Swift 5.7 added stronger index validation for `String`, so some illegal cases that previously triggered inconsistently diagnosed out of bounds accesses now result in reliable runtime errors. Similarly, attempts at applying an index originally vended by a UTF-8 string on a UTF-16 string now result in a reliable runtime error. As is usually the case, new traps to the stdlib exposes code that contains previously undiagnosed / unreliably diagnosed coding issues. Allow invalid code in binaries built with earlier versions of the stdlib to continue running with the 5.7 library by disabling some of the new traps based on the version of Swift the binary was built with. In the case of an index encoding mismatch, allow transcoding of string storage regardless of the direction of the mismatch. (Previously we only allowed transcoding a UTF-8 string to UTF-16.) rdar://93379333 (cherry picked from commit 50c2399)
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@swift-ci test |
stephentyrone
approved these changes
Jun 2, 2022
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(Cherry picked from #58954)
Explanation: Swift 5.7 added stronger index validation for
String, so some illegal cases that previously triggered inconsistently diagnosed out of bounds accesses now result in reliable runtime errors. Similarly, attempts at applying an index originally vended by a UTF-8 string on a UTF-16 string now result in a reliable runtime error.As is usually the case, adding new traps to the stdlib exposes some existing code that contains previously undiagnosed / unreliably diagnosed coding issues. This change allows invalid code inside binaries built with earlier versions of the stdlib to continue running with the 5.7 library by disabling some of the new traps based on the version of Swift the binary was built with.
In the case of an index encoding mismatch, allow transcoding of string storage regardless of the direction of the mismatch. (Previously we only allowed transcoding a UTF-8 string to UTF-16.)
Scope:
Stringin the Standard Library; binary compatibility.Risk: Medium. While the change is relatively large, it merely loosens the Stdlib's preconditions, allowing entry points to succeed in more cases. The primary risk has to do with the introduction of the new bincompat checks, especially as they come with a new stdlib/runtime interface through
SwiftShimsadditions.Issue: rdar://93379333
Reviewer: @glessard