Clarify meaning of ranges in pointer offset docs by RalfJung · Pull Request #156666 · rust-lang/rust

RalfJung · 2026-05-17T12:56:48Z

Supersedes #154370

rustbot · 2026-05-17T12:56:53Z

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RalfJung · 2026-06-02T08:24:16Z

@rust-lang/opsem can one of you review this? Even if you can't r+ that should hopefully help the assigned reviewer.

Speaking of which, it's been two weeks, so let's reroll.
@rustbot reroll

chorman0773

This all looks correct and the implications seem to follow mathematically (and thus are sound).

View changes since this review

jhpratt

@rustbot author

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jhpratt · 2026-06-07T02:13:37Z

+`count` is in units of T; e.g., a `count` of 3 represents a pointer
+offset of `3 * size_of::<T>()` bytes.


Unless I'm misunderstanding what you mean by this, doesn't this mean count * size_of::<T>() later on is effectively N * size_of::<T>() * size_of::<T>(), which is obviously incorrect? On its own, the safety section looks fine, but the addition of this callout seems unusual.

I don't understand what you mean, and I didn't even change this text. Where are we multiplying twice? We are just defining "offset in bytes" twice, once by example in the introduction and once more generally in the safety docs.

This is the equivalent of

let offset_in_bytes = count * size; let offset_in_bytes = count * size;

The bit I highlighted sounds like you're defining count, not "offset in bytes".

I read this 5 times now and I cannot figure out which part of it sounds to you like it defines count. It defines how to interpret count. count is a function argument given by the user, we cannot define it.

Since this is the same wording we already have on stable and had for many years, can we move this discussion into an issue or so? It's not really about the changes this PR proposes.

Yup, I didn't realize that was pre-existing. I don't care enough to open an issue for this; it's moreso that I found it confusing at first read.

@bors r+ rollup

rust-bors · 2026-06-07T20:25:19Z

📌 Commit f0ef8a9 has been approved by jhpratt

It is now in the queue for this repository.

Rollup of 25 pull requests Successful merges: - #157447 (Move cross crate tests into the appropriate folder) - #145108 (Resolver: Batched Import Resolution) - #156119 (Further optimize `SliceIndex<str>` impl for `Range<usize>`) - #157224 (Manually unroll loop in `str::floor_char_boundary`) - #157289 (Add infallible primitive type lookups to template arg resolver) - #157540 (Cleanup and optimize `render_impls`) - #157444 (Couple of work product cleanups) - #157543 (Reorganize `tests/ui/issues` [5/N]) - #153513 (Syntactically reject equality predicates) - #155797 (LineWriter: cap write_vectored newline scan to avoid quadratic write_all_vectored) - #156155 (macros: report unbound metavariables directly) - #156188 (riscv: promote d, e, and f target_features to CfgStableToggleUnstable) - #156666 (Clarify meaning of ranges in pointer offset docs) - #157078 (Document equivalence of `highest_one` and `ilog2` methods on integers) - #157129 (ci: update download-artifact action to v8) - #157169 (triagebot: Update messages to direct changes to appropriate repositories) - #157323 (Document Repeat::last panic behavior) - #157370 (Clarify MaybeUninit::zeroed padding docs) - #157399 (Silence llbc's output by default to prevent rustc's linker output warning) - #157500 (Improve documentation of `align_of` and `Alignment`.) - #157545 (Suggest using comma to separate valid attribute list items) - #157559 (chore: Update annotate-snippets to 0.12.16) - #157560 (In `copy_nonoverlapping`, use `mul nuw nsw` to compute the byte size) - #157580 (Importing suggestion reported twice when reporting privacy error) - #157581 (Test fixup)

Rollup merge of #156666 - RalfJung:offset-ranges, r=jhpratt Clarify meaning of ranges in pointer offset docs Supersedes #154370

Rollup of 25 pull requests Successful merges: - rust-lang/rust#157447 (Move cross crate tests into the appropriate folder) - rust-lang/rust#145108 (Resolver: Batched Import Resolution) - rust-lang/rust#156119 (Further optimize `SliceIndex<str>` impl for `Range<usize>`) - rust-lang/rust#157224 (Manually unroll loop in `str::floor_char_boundary`) - rust-lang/rust#157289 (Add infallible primitive type lookups to template arg resolver) - rust-lang/rust#157540 (Cleanup and optimize `render_impls`) - rust-lang/rust#157444 (Couple of work product cleanups) - rust-lang/rust#157543 (Reorganize `tests/ui/issues` [5/N]) - rust-lang/rust#153513 (Syntactically reject equality predicates) - rust-lang/rust#155797 (LineWriter: cap write_vectored newline scan to avoid quadratic write_all_vectored) - rust-lang/rust#156155 (macros: report unbound metavariables directly) - rust-lang/rust#156188 (riscv: promote d, e, and f target_features to CfgStableToggleUnstable) - rust-lang/rust#156666 (Clarify meaning of ranges in pointer offset docs) - rust-lang/rust#157078 (Document equivalence of `highest_one` and `ilog2` methods on integers) - rust-lang/rust#157129 (ci: update download-artifact action to v8) - rust-lang/rust#157169 (triagebot: Update messages to direct changes to appropriate repositories) - rust-lang/rust#157323 (Document Repeat::last panic behavior) - rust-lang/rust#157370 (Clarify MaybeUninit::zeroed padding docs) - rust-lang/rust#157399 (Silence llbc's output by default to prevent rustc's linker output warning) - rust-lang/rust#157500 (Improve documentation of `align_of` and `Alignment`.) - rust-lang/rust#157545 (Suggest using comma to separate valid attribute list items) - rust-lang/rust#157559 (chore: Update annotate-snippets to 0.12.16) - rust-lang/rust#157560 (In `copy_nonoverlapping`, use `mul nuw nsw` to compute the byte size) - rust-lang/rust#157580 (Importing suggestion reported twice when reporting privacy error) - rust-lang/rust#157581 (Test fixup)

RalfJung added 3 commits May 17, 2026 14:29

move ptr::sub docs into its own file (matching add, offset)

2cf09e1

offset, add, sub: make the range we are talking about more explicit

9dc2496

also use shared pointer offset/add/sub docs for NonNull

f0ef8a9

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels May 17, 2026

rustbot assigned Mark-Simulacrum May 17, 2026

RalfJung mentioned this pull request May 17, 2026

Clarify one-past-the-end pointer validity #154370

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rustbot assigned jhpratt and unassigned Mark-Simulacrum Jun 2, 2026

chorman0773 approved these changes Jun 4, 2026

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jhpratt reviewed Jun 7, 2026

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 7, 2026

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 7, 2026

jhpratt mentioned this pull request Jun 7, 2026

Rollup of 25 pull requests #157586

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rust-bors Bot merged commit 035bf16 into rust-lang:main Jun 8, 2026
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rustbot added this to the 1.98.0 milestone Jun 8, 2026

rust-timer added a commit that referenced this pull request Jun 8, 2026

Unrolled build for #156666

cc65dc8

Rollup merge of #156666 - RalfJung:offset-ranges, r=jhpratt Clarify meaning of ranges in pointer offset docs Supersedes #154370

RalfJung deleted the offset-ranges branch June 9, 2026 10:50

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Clarify meaning of ranges in pointer offset docs#156666

Clarify meaning of ranges in pointer offset docs#156666
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		`count` is in units of T; e.g., a `count` of 3 represents a pointer
		offset of `3 * size_of::<T>()` bytes.

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