[5.3] [Function builders] Use buildLimitedAvailability() for #available block #32995
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The use of "if #available" in function builders can subvert availability checking if the function builder carries all type information for the values within the "then" block outside of the "else" block. Tighten up the model in two ways: * Check whether the type coming out of an "if #available" references any declarations that are not available in the outer context, to close up the model. * If the function builder provides a buildLimitedAvailability(_:) operation, call that on the result of the "then" block in an "if that it cannot leak out of the "if #available"; if it doesn't, the check above will still fire. Stage this in with a warning so function builders out there in the wild can adapt. We'll upgrade the warning to an error later. Fixes rdar://problem/65021017.
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devincoughlin
approved these changes
Jul 21, 2020
AnthonyLatsis
added
swift 5.3
🍒 release cherry pick
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The use of "if #available" in function builders can subvert availability
checking if the function builder carries all type information for the
values within the "then" block outside of the "else" block. Tighten up
the model in two ways:
any declarations that are not available in the outer context, to close
up the model.
operation, call that on the result of the "then" block in an "if
that it cannot leak out of the "if #available"; if it doesn't, the
check above will still fire.
Stage this in with a warning so function builders out there in the wild
can adapt. We'll upgrade the warning to an error later.
Fixes rdar://problem/65021017.
Original: #32994