Fix weak_ptr conversions, preserving control blocks for expired objects - #1104
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Stephan T. Lavavej (StephanTLavavej) merged 3 commits intoAug 1, 2020
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Fixes #1102. This adds a few comments to the product code, explaining what's going on. Then, I enhanced our existing test for
weak_ptrconversions to testowner_beforeand then useowner_beforeto test that control blocks are preserved. Finally, I added a small test for the behavior of virtual inheritance conversions before the object expired, since we weren't actually testing that.Performance note: it would be possible to detect
T*toconst T*and avoid the_Incref_nz(which we did before this PR too, in the form of_Other.lock()); I could file an issue about that after merging this PR if anyone is interested. At this time, we don't know if it's possible to detect virtual base traversal in general, without a compiler builtin.