[wip] Introduce Ptr::project_map
#2984
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Summary of ChangesHello @jswrenn, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed! This pull request introduces a significant enhancement to pointer manipulation by adding a Highlights
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Code Review
This pull request introduces Ptr::project_map to enable piecewise initialization of data structures. This is a valuable addition. The supporting machinery, including the invariant::Map trait and its implementation for tuples, seems correct.
However, the implementation of project_map itself in src/pointer/ptr.rs has a critical soundness issue. It uses unsafe { self.assume_validity() } without proper justification, and the logic seems to incorrectly handle the result of the mapping closure. As indicated by the // SAFETY: TODO comment, this is likely a work in progress, but it's crucial to address this before merging.
| let _mapped = match self.reborrow().project() { | ||
| Ok(field) => map(field), | ||
| Err(err) => return Err(err), | ||
| }; | ||
| // SAFETY: TODO | ||
| Ok(unsafe { self.assume_validity() }) | ||
| } |
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This implementation has a critical soundness issue.
The map closure is called on a reborrow of self, and its resulting Ptr is immediately discarded (assigned to _mapped). This means any type-level proof of a validity change is lost.
Subsequently, unsafe { self.assume_validity() } is called without justification. Since map operated on a temporary borrow, it cannot logically change the validity of the original self. This unsafe block is unsound as written and, as the // SAFETY: TODO comment indicates, lacks the required safety proof.
This could lead to Ptrs with incorrect validity invariants, causing undefined behavior. The map closure's returned Ptr must be used to prove that the operation is sound before assume_validity can be justified.
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Enables piecewise initialization. gherrit-pr-id: Gc3e9ee9afa6945e10c35be84d30c970894395c96
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Enables piecewise initialization.
TryFromBytes::Uninit#3021Ptr::project_map#2984Ptrvalidity #2966Latest Update: v4 — Compare vs v3
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git fetch origin refs/heads/Gc3e9ee9afa6945e10c35be84d30c970894395c96 && git checkout -b pr-Gc3e9ee9afa6945e10c35be84d30c970894395c96 FETCH_HEADCheckout
git fetch origin refs/heads/Gc3e9ee9afa6945e10c35be84d30c970894395c96 && git checkout FETCH_HEADCherry Pick
git fetch origin refs/heads/Gc3e9ee9afa6945e10c35be84d30c970894395c96 && git cherry-pick FETCH_HEADPull
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