Implement workaround for LLVM-46269 by ensuring that constrained destructor appears after the unconstrained one #2630
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miscco
reviewed
Apr 1, 2022
miscco
approved these changes
Apr 1, 2022
CaseyCarter
reviewed
Apr 1, 2022
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Thanks bunches for jumping on this so quickly. I've added this PR to my list of things to ensure are in the 16.11 backport. |
CaseyCarter
approved these changes
Apr 1, 2022
StephanTLavavej
approved these changes
Apr 1, 2022
Comment on lines
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| // To test the correct specialization of _Defaultabox, this type must not be default constructible. | ||
| non_trivially_destructible_input_iterator() = delete; |
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I'm surprised that this doesn't trigger compiler warnings about "this class has no constructors" (usually I'd expect to see an (int, int) constructor or something similar to avoid this), but no change requested as there are apparently no test-breaking warnings.
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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Thanks for improving our Clang support! 😻 🐞 🎉 |
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This implements workaround for LLVM-46269 ("Only first destructor is considered when constraints are used").
If the constrained (and defaulted) destructor comes first, clang-cl uses it unconditionally, even if its constraints are not satisfied. This leads to an error when the defaulted destructor is implicitly deleted (due to a non-trivially-destructible member).
By moving the constrained destructor after the unconstrained one (which is always valid, but is non-trivial), this patch sidesteps the abovementioned error.
This is suboptimal, because this makes the affected types never trivially destructible when compiled with clang-cl. A perfect fix would need to use something akin to the existing
_Optional_destruct_base, which I assume that we want to avoid.