[5.7][stdlib] Switch to using unchecked buffer subscript in low-level Unicode helpers #59901
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…ode helpers We expect indices to be already validated by the time these are called, and UBP’s debug-mode checks are compiled into opaque parts of the stdlib. (The big exception is that Swift <5.7 used to not do proper index validation and allowed out-of-bounds accesses. We emulate this behavior for code that was compiled with such a release, and it turns out that these UnsafeBufferPointer checks are interfering with the intended (undefined) behavior.) rdar://93707276 (cherry picked from commit 64a57e3)
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@swift-ci test |
lorentey
changed the title
stephentyrone
approved these changes
Jul 6, 2022
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(cherry picked from #59899)
Description: This fixes a minor binary compatibility issue by allowing invalid String indices to be passed to some String operations without a runtime trap, as long as the binary was built with Swift 5.6 or earlier. This allows broken code to keep "working" as it did in earlier Standard Library releases, while still allowing us to catch & report the issue for binaries compiled with the new SDK.
Risk: Low. This eliminates some low-level checks that were already supposed to have been done by the time this code is called. The primary risk is that in some cases these checks may be our last safety net against out-of-bounds access.
Review by: @glessard & @Azoy
Testing: Regular regression testing, plus manual bincompat verification.
Original PR: #59899
Issue: rdar://93707276