[5.4] Narrowly Fix a Crash in Availability Checking of Defer Bodies #36108
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This reverts commit ae711a7.
NIO exposed an issue in the new availability walkers where an implicit check was not being performed. They were able to get this to crash by using a defer statement - the body of which contains implicit declarations that got run through the walker. This exposed a wider hole in availability checking of defer statements. Namely, that it wasn't happening. This is a narrow fix (as opposed to the broader fix in swiftlang#36102) that is safer to take for Swift 5.4. rdar://74484150
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tkremenek
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Feb 23, 2021
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NIO exposed an issue in the new availability walkers where an implicit
check was not being performed. They were able to get this to crash by
using a defer statement - the body of which contains implicit
declarations that got run through the walker. This exposed a wider hole
in availability checking of defer statements. Namely, that it wasn't
happening.
This is a narrow fix (as opposed to the broader fix in
#36102) that is safer to take for
Swift 5.4.
rdar://74484150