[5.9][move-only] Ban partial reinitialization after consuming a value. #67146
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Original: #67145 |
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jckarter
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Jul 6, 2023
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This looks good. There's a decent amount of new code, but it's in service to the new diagnostic, so it should be self-contained. We do want this diagnostic so we don't end up having to support code that does partial initializations before we hammer the semantics out.
(cherry picked from commit 7e582b0)
This is similar to our ban on partial consuming a value for this release. The
reason for this is that, one can achieve a similar affect as partial consumption
via a consumption of the entire value and then a partial reinitialization. Example:
```swift
struct X : ~Copyable { var i = 5, var i2 = Klass() }
var x = X()
_ = consume x
x.i = 5
```
in the case above, we now have a value that is in a partially initialized state.
We still allow for move only types to have their fields initialized as long as
there is an intervening init.
rdar://111498740
(cherry picked from commit 69a03c9)
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DougGregor
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Jul 6, 2023
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• Description: [5.9][move-only] Ban partial reinitialization after consuming a value. The language impact of this is that we want to be sure that partially reinitializing after consuming a value, results in an error:
The reason why we want to do this is that the original proposal said values were never partially initialized. We already have banned partial consumption, but we realized that this was another way to create a partially alive value. Given that, we want to go through a round of forum discussion at least before we put this out there. This closes the hole in the mean time.
• Risk: This is low risk since it only affects a corner case in a specific part of the noncopyable checker. So it cannot affect anything but noncopyable code.
• Original PR: #67145
• Reviewed By: @jckarter
• Testing: Added Swift tests
• Resolves: rdar://111498740