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[lint request] unspecified_repr_Rust_transmute #3999

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gnzlbg opened this issue Apr 18, 2019 · 1 comment
Open

[lint request] unspecified_repr_Rust_transmute #3999

gnzlbg opened this issue Apr 18, 2019 · 1 comment
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A-lint Area: New lints

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@gnzlbg
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gnzlbg commented Apr 18, 2019

There are some repr(Rust) types (structs, tuples, tuple structs, enums, unions, ...) for which we guarantee the layout (e.g. Option<NonZeroU32>), but we don't guarantee the layout of most repr(Rust) types, their layout is unspecified and allowed to change.

We should add a lint that warns about these, but I think we should try to at least compile a list of cases for which we do guarantee layout, and not warn on those.

cc @eddyb
@matthiaskrgr matthiaskrgr added the A-lint Area: New lints label Apr 19, 2019
@oli-obk
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oli-obk commented Apr 24, 2019

Maybe we can "document" these in the ty::Layout so semverver can use the same logic for figuring out when changing a type is a breaking change (moving from guaranteed layout to not guaranteed layout on a public type is a breaking change)

@Jarcho Jarcho mentioned this issue Feb 6, 2022
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bors added a commit that referenced this issue Feb 6, 2022
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Auto merge of #8398 - Jarcho:unordered_transmute, r=llogiq
093e320 
Add lint `transmute_undefined_repr`

Partially implements #3999 and #546

This doesn't consider `enum`s at all right now as those are going to be a pain to deal with. This also allows `#[repr(Rust)]` structs with only one non-zero sized fields. I think those are technically undefined when transmuted.

changelog: Add lint `transmute_undefined_repr`
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@oli-obk @matthiaskrgr @gnzlbg