other-reprs: do not make it sound like we are making ABI promises for repr(int) enums #461
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RalfJung
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CAD97
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Sep 11, 2024
| knowledge of "invalid" values at this type to optimize enum layout, such as when | ||
| this enum is wrapped in `Option`). Note that the function call ABI for these | ||
| types is still in general unspecified, except that across `extern "C"` calls they | ||
| are ABI-compatible with C enums of the same sign and size. |
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Just to point this out here as well, C has non-transitive rules that allow enum and the underlying integer type to be punned by ABI.
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Yeah I saw that comment in the issue. I don't think that's something to discuss here though -- they key point is that the Rust thing matches the C thing.
Non-transitive compatibility doesn't really make sense IMO but that's a discussion for another day.
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I've run into problems with cfi tags on methods involving enums in the signature. You probably want to be careful about what you promise here. Unfortunately I don't know what the precise rules are CFI wise.
ehuss
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Feb 19, 2025
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Update books ## rust-lang/book 2 commits in d4d2c18cbd20876b2130a546e790446a8444cb32..4a01a9182496f807aaa5f72d93a25ce18bcbe105 2025-02-24 14:48:34 UTC to 2025-02-13 19:29:47 UTC - Fix typos in chapter 17 (rust-lang/book#4238) - NoStarch backports (rust-lang/book#4224) ## rust-lang/edition-guide 2 commits in 8dbdda7cae4fa030f09f8f5b63994d4d1dde74b9..daa4b763cd848f986813b5cf8069e1649f7147af 2025-02-22 14:58:51 UTC to 2025-02-21 02:30:17 UTC - Remove precise capturing features (rust-lang/edition-guide#362) - use same name as previous example (rust-lang/edition-guide#360) ## rust-lang/nomicon 1 commits in 336f75835a6c0514852cc65aba9a698b699b13c8..8f5c7322b65d079aa5b242eb10d89a98e12471e1 2025-02-19 13:16:47 UTC to 2025-02-19 13:16:47 UTC - other-reprs: do not make it sound like we are making ABI promises for repr(int) enums (rust-lang/nomicon#461) ## rust-lang/reference 4 commits in 6195dbd70fc6f0980c314b4d23875ac570d8253a..615b4cec60c269cfc105d511c93287620032d5b0 2025-02-18 23:01:53 UTC to 2025-02-13 15:12:49 UTC - Add rule identifiers to names chapters (rust-lang/reference#1737) - Switch from AVX to SSE in the example (rust-lang/reference#1735) - Remove attributes from struct field rest patterns (rust-lang/reference#1736) - Update reference for target_feature_11. (rust-lang/reference#1720)
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Rollup merge of rust-lang#137552 - rustbot:docs-update, r=ehuss Update books ## rust-lang/book 2 commits in d4d2c18cbd20876b2130a546e790446a8444cb32..4a01a9182496f807aaa5f72d93a25ce18bcbe105 2025-02-24 14:48:34 UTC to 2025-02-13 19:29:47 UTC - Fix typos in chapter 17 (rust-lang/book#4238) - NoStarch backports (rust-lang/book#4224) ## rust-lang/edition-guide 2 commits in 8dbdda7cae4fa030f09f8f5b63994d4d1dde74b9..daa4b763cd848f986813b5cf8069e1649f7147af 2025-02-22 14:58:51 UTC to 2025-02-21 02:30:17 UTC - Remove precise capturing features (rust-lang/edition-guide#362) - use same name as previous example (rust-lang/edition-guide#360) ## rust-lang/nomicon 1 commits in 336f75835a6c0514852cc65aba9a698b699b13c8..8f5c7322b65d079aa5b242eb10d89a98e12471e1 2025-02-19 13:16:47 UTC to 2025-02-19 13:16:47 UTC - other-reprs: do not make it sound like we are making ABI promises for repr(int) enums (rust-lang/nomicon#461) ## rust-lang/reference 4 commits in 6195dbd70fc6f0980c314b4d23875ac570d8253a..615b4cec60c269cfc105d511c93287620032d5b0 2025-02-18 23:01:53 UTC to 2025-02-13 15:12:49 UTC - Add rule identifiers to names chapters (rust-lang/reference#1737) - Switch from AVX to SSE in the example (rust-lang/reference#1735) - Remove attributes from struct field rest patterns (rust-lang/reference#1736) - Update reference for target_feature_11. (rust-lang/reference#1720)
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Until something like rust-lang/rust#128600 lands, let's be careful what we say about this.
Also mention that
repr(C)generally makes this behave the same as C ABI-wise. That's anyway what people already assume this means and are relying on in practice, so there's no point in not saying it IMO?Cc @rust-lang/opsem @chorman0773