[pointer][invariant] Remove AliasingMapping, Inaccessible (#2301) #2386
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We previously used `AliasingMapping`s and `Inaccessible` to model `UnsafeCell` agreement. This abuses the notion of a mapping since one doesn't ever actually want to change the aliasing of a pointer (and certainly not to `Inaccessible`) - really this was meant to model pointer casts which should never be performed. In addition to being an awkward fit, the presence of `Inaccessible` meant that code could not assume that any `Aliasing` invariant permitted reading, and so we had to add extra machinery to work around this. Future commits will use a different, simpler model for denoting `UnsafeCell` agreement or disagreement. While we're here, make `Read` slightly more permissive, implemented for `A: Aliasing, T: Immutable` rather than just `A: Reference, T: Immutable`. Makes progress on #1122, #1866 gherrit-pr-id: I1ac2ae177a235083e33b09fc848423220d3da042
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Backporting #2301 |
jswrenn
approved these changes
Feb 25, 2025
Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## v0.8.x #2386 +/- ##
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Coverage 87.81% 87.81%
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Files 17 17
Lines 6195 6195
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Hits 5440 5440
Misses 755 755 ☔ View full report in Codecov by Sentry. |
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We previously used
AliasingMappings andInaccessibleto modelUnsafeCellagreement. This abuses the notion of a mapping since one doesn't ever actually want to change the aliasing of a pointer (and certainly not toInaccessible) - really this was meant to model pointer casts which should never be performed. In addition to being an awkward fit, the presence ofInaccessiblemeant that code could not assume that anyAliasinginvariant permitted reading, and so we had to add extra machinery to work around this.Future commits will use a different, simpler model for denoting
UnsafeCellagreement or disagreement.While we're here, make
Readslightly more permissive, implemented forA: Aliasing, T: Immutablerather than justA: Reference, T: Immutable.Makes progress on #1122, #1866
gherrit-pr-id: I1ac2ae177a235083e33b09fc848423220d3da042