Disable field reordering for repr(int). #56887
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The order of commits is the opposite github shows because github doesn't show the topological order... :( Anyway. cc @BorisChiou, I think this is the problem you hit with cbindgen that time. |
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RFC rust-lang#2195 specifies that a repr(int) enum such as: #[repr(u8)] enum MyEnum { B { x: u8, y: i16, z: u8 }, } has a layout that is equivalent to: #[repr(C)] enum MyEnumVariantB { tag: u8, x: u8, y: i16, z: u8 }, However this isn't actually implemented, with the actual layout being roughly equivalent to: union MyEnumPayload { B { x: u8, y: i16, z: u8 }, } #[repr(packed)] struct MyEnum { tag: u8, payload: MyEnumPayload, } Thus the variant payload is *not* subject to repr(C) ordering rules, and gets re-ordered as `{ x: u8, z: u8, z: i16 }` The existing tests added in pull-req rust-lang#45688 fail to catch this as the repr(C) ordering just happens to match the current Rust ordering in this case; adding a third field reveals the problem.
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| pub fn inhibit_struct_field_reordering_opt(&self) -> bool { | ||
| !(self.flags & ReprFlags::IS_UNOPTIMISABLE).is_empty() || (self.pack == 1) | ||
| self.flags.intersects(ReprFlags::IS_UNOPTIMISABLE) || self.pack == 1 || | ||
| self.int.is_some() |
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cc @rkruppe @nagisa This seems somewhat fragile (I mean the pre-existing code).
The check for pack == 1 means things will still be reordered with #[repr(packed(N))], is that intentional?
Also, it seems to me that inhibit_enum_layout_opt is a subset of this function and maybe we should have just one function that checks all conditions?
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The repr RFC does not specify any behaviour /wrt repr(packed(N)) for enums and I’m not sure I recall us guaranteeing that repr(packed) specifies any representation and the reference seems to agree.
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In fact as per strict reading of the reference, self.pack == 1 inhibiting reordering would be somewhat wrong, as it should cause "packing" for the original ordering, but since the "default" ordering is not specified, it seems to be fine either way...
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@bors r+ |
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📌 Commit d84bdba has been approved by |
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Disable field reordering for repr(int). This fixes the problem that the test in rust-lang#56619 uncovers. Closes rust-lang#56619.
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Disable field reordering for repr(int). This fixes the problem that the test in rust-lang#56619 uncovers. Closes rust-lang#56619.
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Disable field reordering for repr(int). This fixes the problem that the test in rust-lang#56619 uncovers. Closes rust-lang#56619.
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Rollup of 20 pull requests Successful merges: - #56802 (Add DoubleEndedIterator::nth_back) - #56842 (Add unstable VecDeque::rotate_{left|right}) - #56869 (Reduce search-index.js size) - #56887 (Disable field reordering for repr(int).) - #56892 (rustc: Update Clang used to build LLVM on Linux) - #56909 (static eval: Do not ICE on layout size overflow) - #56914 (Ignore ui/target-feature-gate on sparc, sparc64, powerpc, powerpc64 and powerpc64le) - #56917 (Simplify MIR generation for logical operations) - #56919 (Remove a wrong multiplier on relocation offset computation) - #56933 (Add --progress to git submodule commands in x.py) - #56941 (deny intra-doc link resolution failures in libstd) - #56964 (Remove `TokenStream::JointTree`.) - #56970 (Mem uninit doc ptr drop) - #56973 (make basic CTFE tracing available on release builds) - #56979 (Adding unwinding support for x86_64_fortanix_unknown_sgx target.) - #56981 (miri: allocation is infallible) - #56984 (A few tweaks to dropck_outlives) - #56989 (Fix compiletest `trim` deprecation warnings) - #56992 (suggest similar lint names for unknown lints) - #57002 (Stabilize Vec(Deque)::resize_with) Failed merges: r? @ghost
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Rollup of 20 pull requests Successful merges: - #56802 (Add DoubleEndedIterator::nth_back) - #56842 (Add unstable VecDeque::rotate_{left|right}) - #56869 (Reduce search-index.js size) - #56887 (Disable field reordering for repr(int).) - #56892 (rustc: Update Clang used to build LLVM on Linux) - #56909 (static eval: Do not ICE on layout size overflow) - #56914 (Ignore ui/target-feature-gate on sparc, sparc64, powerpc, powerpc64 and powerpc64le) - #56917 (Simplify MIR generation for logical operations) - #56919 (Remove a wrong multiplier on relocation offset computation) - #56933 (Add --progress to git submodule commands in x.py) - #56941 (deny intra-doc link resolution failures in libstd) - #56964 (Remove `TokenStream::JointTree`.) - #56970 (Mem uninit doc ptr drop) - #56973 (make basic CTFE tracing available on release builds) - #56979 (Adding unwinding support for x86_64_fortanix_unknown_sgx target.) - #56981 (miri: allocation is infallible) - #56984 (A few tweaks to dropck_outlives) - #56989 (Fix compiletest `trim` deprecation warnings) - #56992 (suggest similar lint names for unknown lints) - #57002 (Stabilize Vec(Deque)::resize_with) Failed merges: r? @ghost
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Disable field reordering for repr(int). This fixes the problem that the test in rust-lang#56619 uncovers. Closes rust-lang#56619.
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@bors p=30 (rollup fairness) |
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☀️ Test successful - status-appveyor, status-travis |
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This fixes the problem that the test in #56619 uncovers.
Closes #56619.