[pointer][invariant] Remove AliasingMapping, Inaccessible #2301
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This was referenced Feb 5, 2025
jswrenn
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Feb 5, 2025
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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Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## main #2301 +/- ##
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Coverage 89.93% 89.93%
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Files 16 16
Lines 5833 5833
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Hits 5246 5246
Misses 587 587 ☔ View full report in Codecov by Sentry. |
joshlf
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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 in #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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We previously used
AliasingMappings andInaccessibleto modelUnsafeCellagreement. This abuses the notion of a mapping since onedoesn't ever actually want to change the aliasing of a pointer (and
certainly not to
Inaccessible) - really this was meant to modelpointer casts which should never be performed. In addition to being an
awkward fit, the presence of
Inaccessiblemeant that code could notassume that any
Aliasinginvariant permitted reading, and so we had toadd 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
This PR is on branch ptr-overhaul-more-generic-issue-1945.