Document metadata of ptrs to indirectly unsized types#2289
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We say that pointers to DSTs store metadata and what that metadata is for pointers to slices, `str`, and trait objects. But a struct or tuple with an unsized tail is itself a DST, and we hadn't said what the metadata is for pointers to these unsized types. Now that we've defined *metadata* and *unsized tail*, let's complete this enumeration.
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This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed. Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers. |
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Update books ## rust-lang/nomicon 1 commits in cc6a6bae8c3bfa389974e533c54694662c1a9de6..5012a37c682b26c4e19433888ed2ca9b129696ca 2026-06-25 10:05:58 UTC to 2026-06-25 10:05:58 UTC - Clarify when safety may rely on correctness (rust-lang/nomicon#523) ## rust-lang/reference 10 commits in 2c27905c15a51983b54d84f050d3bda096194d27..86635e30bf861a038dc197d7e16fd09e7e514e7a 2026-06-25 17:00:32 UTC to 2026-06-16 18:56:35 UTC - use-declarations.md: move example to where it's described (rust-lang/reference#2295) - fix link target (rust-lang/reference#2299) - remove broken text (rust-lang/reference#2297) - type-layout: rewrite `#[repr(C)]` struct layout algorithm (rust-lang/reference#2243) - Fix grammar rules containing or pertaining to bounds (rust-lang/reference#2257) - Document metadata of ptrs to indirectly unsized types (rust-lang/reference#2289) - Generalize the wide-pointer total-size bound (rust-lang/reference#2290) - Cover `str` in the wide-pointer metadata rule (rust-lang/reference#2288) - Define an unsized tail (rust-lang/reference#2287) - Define pointer metadata (rust-lang/reference#2286)
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We say that pointers to DSTs store metadata and what that metadata is for pointers to slices,
str, and trait objects. But a struct or tuple with an unsized tail is itself a DST, and we hadn't said what the metadata is for pointers to these unsized types.Now that we've defined metadata and unsized tail, let's complete this enumeration.
I'm breaking this out from #2282 so that we can merge the prerequisites before considering the new lang guarantees.
This is stacked on #2286 and #2287 and #2288 and #2290 (yes, that one is out of order) and those should be merged first.
cc @ehuss @RalfJung @Mark-Simulacrum