[kixelated]

Problem

offset_from between two byte pointers into one buffer threw rust2-ts: offset_from of pointers JS keeps in different arrays when they came through different views of it. Example: a slice's as_mut_ptr and the pointer of an element its iter_mut gives. Native Rust measures the distance. Each pointer is an rt.AtIndex into its own Uint8Array, and subarray makes a fresh one sharing the buffer. Found by review on #418 and recorded in quest/m3/ts-unsafe.md.

Approach

rt.ptrOffsetFrom treats two Uint8Arrays over one ArrayBuffer as one array, measuring by each view's byteOffset plus the pointer's index. Every other pair of arrays still fails loudly. It is the only runtime operation that compares a pointer's array by identity: ptr::copy already copies between views through Uint8Array.set, and translation refuses comparisons of element pointers.

Impact

• Output: unchanged.
• Runtime: rt.ptrOffsetFrom returns the distance where it threw. No public API change, no MIGRATE.md entry.
• Quest: drops the item from quest/m3/ts-unsafe.md.

Tests: fixtures/lang/src/elements.rs's edges, differential against native wasm32: within a subslice of a byte array, pointers from as_mut_ptr, from iter_mut's first and last elements, and from split_at_mut's second part, measured against each other both ways, then a write through a pointer moved by one such distance. Before the fix, those cases threw (181 differences); after it, they agree with native.

Alternatives

• One canonical Uint8Array per buffer, made by elemOf. Rejected: it would also let a pointer reach past its view into the rest of the buffer, such as a ByteVec's spare capacity, which today fails loudly. That needs its own decision.

Review

• quest review by Codex, gpt-6.1-sol, medium effort. Round 1 on 894deeaf: clean. Then main merged (feat(ts): hold a value by ManuallyDrop as the value, dropped only when asked #425 and fix(ffi): move a clone out of C++'s last shared copy while a future borrows it #451, conflict-free).
• just ci passes locally on 0c64752339919d3f2146687254d5dbb002685cef (one commit behind main, feat(ts): translate &mut dyn Debug and &mut dyn Display #453, which touches only fmt).

(written by Claude Opus 5.5)

🤖 Generated with Claude Code

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