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Auto merge of #113245 - lukas-code:unsizing-sanity-check, r=the8472

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sanity check field offsets in unsizeable structs

As promised in https://github.com/rust-lang/rust/pull/112062#issuecomment-1567494994, this PR extends the layout sanity checks to ensure that structs fields don't move around when unsizing and prevent issues like https://github.com/rust-lang/rust/issues/112048 in the future. Like most other layout sanity checks, this only runs on compilers with debug assertions enabled.

Here is how it looks when it fails:
```text
error: internal compiler error: compiler/rustc_ty_utils/src/layout.rs:533:21: unsizing GcNode<std::boxed::Box<i32>> changed field order!
                                Layout { size: Size(32 bytes), align: AbiAndPrefAlign { abi: Align(8 bytes), pref: Align(8 bytes) }, abi: Aggregate { sized: true }, fields: Arbitrary { offsets: [Size(0 bytes), Size(8 bytes), Size(24 bytes)], memory_index: [0, 1, 2] }, largest_niche: Some(Niche { offset: Size(24 bytes), value: Pointer(AddressSpace(0)), valid_range: 1..=18446744073709551615 }), variants: Single { index: 0 } }
                                Layout { size: Size(24 bytes), align: AbiAndPrefAlign { abi: Align(8 bytes), pref: Align(8 bytes) }, abi: Aggregate { sized: false }, fields: Arbitrary { offsets: [Size(16 bytes), Size(0 bytes), Size(24 bytes)], memory_index: [1, 0, 2] }, largest_niche: None, variants: Single { index: 0 } }
```

r? `@the8472`
This commit is contained in:
bors 2023-07-07 15:42:29 +00:00
commit cb80ff132a
10 changed files with 107 additions and 56 deletions
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16
compiler/rustc_middle/src/ty/mod.rs
View file

@ -2035,6 +2035,22 @@ impl VariantDef {
&self.fields[FieldIdx::from_u32(0)]
}
/// Returns the last field in this variant, if present.
#[inline]
pub fn tail_opt(&self) -> Option<&FieldDef> {
self.fields.raw.last()
}
/// Returns the last field in this variant.
///
/// # Panics
///
/// Panics, if the variant has no fields.
#[inline]
pub fn tail(&self) -> &FieldDef {
self.tail_opt().expect("expected unsized ADT to have a tail field")
}
}
impl PartialEq for VariantDef {

4
compiler/rustc_middle/src/ty/util.rs
View file

@ -230,7 +230,7 @@ impl<'tcx> TyCtxt<'tcx> {
if !def.is_struct() {
break;
}
match def.non_enum_variant().fields.raw.last() {
match def.non_enum_variant().tail_opt() {
Some(field) => {
f();
ty = field.ty(self, substs);
@ -304,7 +304,7 @@ impl<'tcx> TyCtxt<'tcx> {
(&ty::Adt(a_def, a_substs), &ty::Adt(b_def, b_substs))
if a_def == b_def && a_def.is_struct() =>
{
if let Some(f) = a_def.non_enum_variant().fields.raw.last() {
if let Some(f) = a_def.non_enum_variant().tail_opt() {
a = f.ty(self, a_substs);
b = f.ty(self, b_substs);
} else {