Add initial support for unsized MaybeUninit wrapper type (#2055)
#2310
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Backporting #2055 |
jswrenn
approved these changes
Feb 6, 2025
This is achieved by adding a `MaybeUninit` associated type to `KnownLayout`, whose layout is identical to `Self` except that it admits uninitialized bytes in all positions. For sized types, this is bound to `mem::MaybeUninit<Self>`. For potentially unsized structs, we synthesize a doppelganger with the same `repr`, whose leading fields are wrapped in `mem::MaybeUninit` and whose trailing field is the `MaybeUninit` associated type of struct's original trailing field type. This type-level recursion bottoms out at `[T]`, whose `MaybeUninit` associated type is bound to `[mem::MaybeUninit<T>]`. Makes progress towards #1797 SKIP_CARGO_SEMVER_CHECKS=1 gherrit-pr-id: Idfc357094e28b54a15d947141241ca2da83dcc91
Codecov ReportAttention: Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #2310 +/- ##
==========================================
- Coverage 89.93% 89.27% -0.67%
==========================================
Files 16 16
Lines 5833 5976 +143
==========================================
+ Hits 5246 5335 +89
- Misses 587 641 +54 ☔ View full report in Codecov by Sentry. |
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This is achieved by adding a
MaybeUninitassociated type toKnownLayout, whose layout is identical toSelfexcept that it admits uninitialized bytes in all positions.For sized types, this is bound to
mem::MaybeUninit<Self>. For potentially unsized structs, we synthesize a doppelganger with the samerepr, whose leading fields are wrapped inmem::MaybeUninitand whose trailing field is theMaybeUninitassociated type of struct's original trailing field type. This type-level recursion bottoms out at[T], whoseMaybeUninitassociated type is bound to[mem::MaybeUninit<T>].Makes progress towards #1797
SKIP_CARGO_SEMVER_CHECKS=1
gherrit-pr-id: Idfc357094e28b54a15d947141241ca2da83dcc91