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Rollup merge of #129217 - jswrenn:transmute-lifetimes, r=compiler-errors

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safe transmute: check lifetimes

Modifies `BikeshedIntrinsicFrom` to forbid lifetime extensions on references. This static check can be opted out of with the `Assume::lifetimes` flag.

Fixes #129097

Tracking Issue: https://github.com/rust-lang/rust/issues/99571

 r​? `@compiler-errors`
This commit is contained in:
Matthias Krüger 2024-08-19 20:14:56 +02:00 committed by GitHub
commit 5cb30b7e9d
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9 changed files with 535 additions and 132 deletions
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176
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
View File

@ -17,8 +17,7 @@ use rustc_infer::infer::{DefineOpaqueTypes, HigherRankedType, InferOk};
use rustc_infer::traits::ObligationCauseCode;
use rustc_middle::traits::{BuiltinImplSource, SignatureMismatchData};
use rustc_middle::ty::{
self, GenericArgs, GenericArgsRef, GenericParamDefKind, ToPolyTraitRef, TraitPredicate, Ty,
TyCtxt, Upcast,
self, GenericArgs, GenericArgsRef, GenericParamDefKind, ToPolyTraitRef, Ty, TyCtxt, Upcast,
};
use rustc_middle::{bug, span_bug};
use rustc_span::def_id::DefId;
@ -292,90 +291,120 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
&mut self,
obligation: &PolyTraitObligation<'tcx>,
) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> {
use rustc_transmute::{Answer, Condition};
#[instrument(level = "debug", skip(tcx, obligation, predicate))]
use rustc_transmute::{Answer, Assume, Condition};
/// Generate sub-obligations for reference-to-reference transmutations.
fn reference_obligations<'tcx>(
tcx: TyCtxt<'tcx>,
obligation: &PolyTraitObligation<'tcx>,
(src_lifetime, src_ty, src_mut): (ty::Region<'tcx>, Ty<'tcx>, Mutability),
(dst_lifetime, dst_ty, dst_mut): (ty::Region<'tcx>, Ty<'tcx>, Mutability),
assume: Assume,
) -> Vec<PredicateObligation<'tcx>> {
let make_transmute_obl = |src, dst| {
let transmute_trait = obligation.predicate.def_id();
let assume = obligation.predicate.skip_binder().trait_ref.args.const_at(2);
let trait_ref = ty::TraitRef::new(
tcx,
transmute_trait,
[
ty::GenericArg::from(dst),
ty::GenericArg::from(src),
ty::GenericArg::from(assume),
],
);
Obligation::with_depth(
tcx,
obligation.cause.clone(),
obligation.recursion_depth + 1,
obligation.param_env,
obligation.predicate.rebind(trait_ref),
)
};
let make_freeze_obl = |ty| {
let trait_ref = ty::TraitRef::new(
tcx,
tcx.require_lang_item(LangItem::Freeze, None),
[ty::GenericArg::from(ty)],
);
Obligation::with_depth(
tcx,
obligation.cause.clone(),
obligation.recursion_depth + 1,
obligation.param_env,
trait_ref,
)
};
let make_outlives_obl = |target, region| {
let outlives = ty::OutlivesPredicate(target, region);
Obligation::with_depth(
tcx,
obligation.cause.clone(),
obligation.recursion_depth + 1,
obligation.param_env,
obligation.predicate.rebind(outlives),
)
};
// Given a transmutation from `&'a (mut) Src` and `&'dst (mut) Dst`,
// it is always the case that `Src` must be transmutable into `Dst`,
// and that that `'src` must outlive `'dst`.
let mut obls = vec![make_transmute_obl(src_ty, dst_ty)];
if !assume.lifetimes {
obls.push(make_outlives_obl(src_lifetime, dst_lifetime));
}
// Given a transmutation from `&Src`, both `Src` and `Dst` must be
// `Freeze`, otherwise, using the transmuted value could lead to
// data races.
if src_mut == Mutability::Not {
obls.extend([make_freeze_obl(src_ty), make_freeze_obl(dst_ty)])
}
// Given a transmutation into `&'dst mut Dst`, it also must be the
// case that `Dst` is transmutable into `Src`. For example,
// transmuting bool -> u8 is OK as long as you can't update that u8
// to be > 1, because you could later transmute the u8 back to a
// bool and get undefined behavior. It also must be the case that
// `'dst` lives exactly as long as `'src`.
if dst_mut == Mutability::Mut {
obls.push(make_transmute_obl(dst_ty, src_ty));
if !assume.lifetimes {
obls.push(make_outlives_obl(dst_lifetime, src_lifetime));
}
}
obls
}
/// Flatten the `Condition` tree into a conjunction of obligations.
#[instrument(level = "debug", skip(tcx, obligation))]
fn flatten_answer_tree<'tcx>(
tcx: TyCtxt<'tcx>,
obligation: &PolyTraitObligation<'tcx>,
predicate: TraitPredicate<'tcx>,
cond: Condition<rustc_transmute::layout::rustc::Ref<'tcx>>,
assume: Assume,
) -> Vec<PredicateObligation<'tcx>> {
match cond {
// FIXME(bryangarza): Add separate `IfAny` case, instead of treating as `IfAll`
// Not possible until the trait solver supports disjunctions of obligations
Condition::IfAll(conds) | Condition::IfAny(conds) => conds
.into_iter()
.flat_map(|cond| flatten_answer_tree(tcx, obligation, predicate, cond))
.flat_map(|cond| flatten_answer_tree(tcx, obligation, cond, assume))
.collect(),
Condition::IfTransmutable { src, dst } => {
let transmute_trait = obligation.predicate.def_id();
let assume_const = predicate.trait_ref.args.const_at(2);
let make_transmute_obl = |from_ty, to_ty| {
let trait_ref = ty::TraitRef::new(
tcx,
transmute_trait,
[
ty::GenericArg::from(to_ty),
ty::GenericArg::from(from_ty),
ty::GenericArg::from(assume_const),
],
);
Obligation::with_depth(
tcx,
obligation.cause.clone(),
obligation.recursion_depth + 1,
obligation.param_env,
trait_ref,
)
};
let make_freeze_obl = |ty| {
let trait_ref = ty::TraitRef::new(
tcx,
tcx.require_lang_item(LangItem::Freeze, None),
[ty::GenericArg::from(ty)],
);
Obligation::with_depth(
tcx,
obligation.cause.clone(),
obligation.recursion_depth + 1,
obligation.param_env,
trait_ref,
)
};
let mut obls = vec![];
// If the source is a shared reference, it must be `Freeze`;
// otherwise, transmuting could lead to data races.
if src.mutability == Mutability::Not {
obls.extend([make_freeze_obl(src.ty), make_freeze_obl(dst.ty)])
}
// If Dst is mutable, check bidirectionally.
// For example, transmuting bool -> u8 is OK as long as you can't update that u8
// to be > 1, because you could later transmute the u8 back to a bool and get UB.
match dst.mutability {
Mutability::Not => obls.push(make_transmute_obl(src.ty, dst.ty)),
Mutability::Mut => obls.extend([
make_transmute_obl(src.ty, dst.ty),
make_transmute_obl(dst.ty, src.ty),
]),
}
obls
}
Condition::IfTransmutable { src, dst } => reference_obligations(
tcx,
obligation,
(src.lifetime, src.ty, src.mutability),
(dst.lifetime, dst.ty, dst.mutability),
assume,
),
}
}
// We erase regions here because transmutability calls layout queries,
// which does not handle inference regions and doesn't particularly
// care about other regions. Erasing late-bound regions is equivalent
// to instantiating the binder with placeholders then erasing those
// placeholder regions.
let predicate = self
.tcx()
.erase_regions(self.tcx().instantiate_bound_regions_with_erased(obligation.predicate));
let predicate = obligation.predicate.skip_binder();
let Some(assume) = rustc_transmute::Assume::from_const(
self.infcx.tcx,
@ -387,6 +416,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let dst = predicate.trait_ref.args.type_at(0);
let src = predicate.trait_ref.args.type_at(1);
debug!(?src, ?dst);
let mut transmute_env = rustc_transmute::TransmuteTypeEnv::new(self.infcx);
let maybe_transmutable = transmute_env.is_transmutable(
@ -397,7 +427,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
let fully_flattened = match maybe_transmutable {
Answer::No(_) => Err(Unimplemented)?,
Answer::If(cond) => flatten_answer_tree(self.tcx(), obligation, predicate, cond),
Answer::If(cond) => flatten_answer_tree(self.tcx(), obligation, cond, assume),
Answer::Yes => vec![],
};

13
compiler/rustc_transmute/src/layout/mod.rs
View File

@ -63,7 +63,9 @@ pub mod rustc {
use std::fmt::{self, Write};
use rustc_middle::mir::Mutability;
use rustc_middle::ty::{self, Ty};
use rustc_middle::ty::layout::{LayoutCx, LayoutError};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_target::abi::Layout;
/// A reference in the layout.
#[derive(Debug, Hash, Eq, PartialEq, Clone, Copy)]
@ -120,4 +122,13 @@ pub mod rustc {
self != &Self::Primitive
}
}
pub(crate) fn layout_of<'tcx>(
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
ty: Ty<'tcx>,
) -> Result<Layout<'tcx>, &'tcx LayoutError<'tcx>> {
use rustc_middle::ty::layout::LayoutOf;
let ty = cx.tcx.erase_regions(ty);
cx.layout_of(ty).map(|tl| tl.layout)
}
}

141
compiler/rustc_transmute/src/layout/tree.rs
View File

@ -171,10 +171,12 @@ where
#[cfg(feature = "rustc")]
pub(crate) mod rustc {
use rustc_middle::ty::layout::{HasTyCtxt, LayoutCx, LayoutError, LayoutOf};
use rustc_middle::ty::layout::{HasTyCtxt, LayoutCx, LayoutError};
use rustc_middle::ty::{self, AdtDef, AdtKind, List, ScalarInt, Ty, TyCtxt, TypeVisitableExt};
use rustc_span::ErrorGuaranteed;
use rustc_target::abi::{FieldsShape, Size, TyAndLayout, Variants};
use rustc_target::abi::{
FieldIdx, FieldsShape, Layout, Size, TyAndLayout, VariantIdx, Variants,
};
use super::Tree;
use crate::layout::rustc::{Def, Ref};
@ -202,20 +204,18 @@ pub(crate) mod rustc {
}
impl<'tcx> Tree<Def<'tcx>, Ref<'tcx>> {
pub fn from_ty(
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
pub fn from_ty(ty: Ty<'tcx>, cx: LayoutCx<'tcx, TyCtxt<'tcx>>) -> Result<Self, Err> {
use rustc_target::abi::HasDataLayout;
let layout = ty_layout(cx, ty);
if let Err(e) = ty_and_layout.ty.error_reported() {
if let Err(e) = ty.error_reported() {
return Err(Err::TypeError(e));
}
let target = cx.tcx.data_layout();
let pointer_size = target.pointer_size;
match ty_and_layout.ty.kind() {
match ty.kind() {
ty::Bool => Ok(Self::bool()),
ty::Float(nty) => {
@ -233,32 +233,30 @@ pub(crate) mod rustc {
Ok(Self::number(width as _))
}
ty::Tuple(members) => Self::from_tuple(ty_and_layout, members, cx),
ty::Tuple(members) => Self::from_tuple((ty, layout), members, cx),
ty::Array(inner_ty, len) => {
let FieldsShape::Array { stride, count } = &ty_and_layout.fields else {
let FieldsShape::Array { stride, count } = &layout.fields else {
return Err(Err::NotYetSupported);
};
let inner_ty_and_layout = cx.layout_of(*inner_ty)?;
assert_eq!(*stride, inner_ty_and_layout.size);
let elt = Tree::from_ty(inner_ty_and_layout, cx)?;
let inner_layout = ty_layout(cx, *inner_ty);
assert_eq!(*stride, inner_layout.size);
let elt = Tree::from_ty(*inner_ty, cx)?;
Ok(std::iter::repeat(elt)
.take(*count as usize)
.fold(Tree::unit(), |tree, elt| tree.then(elt)))
}
ty::Adt(adt_def, _args_ref) if !ty_and_layout.ty.is_box() => {
match adt_def.adt_kind() {
AdtKind::Struct => Self::from_struct(ty_and_layout, *adt_def, cx),
AdtKind::Enum => Self::from_enum(ty_and_layout, *adt_def, cx),
AdtKind::Union => Self::from_union(ty_and_layout, *adt_def, cx),
}
}
ty::Adt(adt_def, _args_ref) if !ty.is_box() => match adt_def.adt_kind() {
AdtKind::Struct => Self::from_struct((ty, layout), *adt_def, cx),
AdtKind::Enum => Self::from_enum((ty, layout), *adt_def, cx),
AdtKind::Union => Self::from_union((ty, layout), *adt_def, cx),
},
ty::Ref(lifetime, ty, mutability) => {
let ty_and_layout = cx.layout_of(*ty)?;
let align = ty_and_layout.align.abi.bytes_usize();
let size = ty_and_layout.size.bytes_usize();
let layout = ty_layout(cx, *ty);
let align = layout.align.abi.bytes_usize();
let size = layout.size.bytes_usize();
Ok(Tree::Ref(Ref {
lifetime: *lifetime,
ty: *ty,
@ -274,21 +272,20 @@ pub(crate) mod rustc {
/// Constructs a `Tree` from a tuple.
fn from_tuple(
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
members: &'tcx List<Ty<'tcx>>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
match &ty_and_layout.fields {
match &layout.fields {
FieldsShape::Primitive => {
assert_eq!(members.len(), 1);
let inner_ty = members[0];
let inner_ty_and_layout = cx.layout_of(inner_ty)?;
assert_eq!(ty_and_layout.layout, inner_ty_and_layout.layout);
Self::from_ty(inner_ty_and_layout, cx)
let inner_layout = ty_layout(cx, inner_ty);
Self::from_ty(inner_ty, cx)
}
FieldsShape::Arbitrary { offsets, .. } => {
assert_eq!(offsets.len(), members.len());
Self::from_variant(Def::Primitive, None, ty_and_layout, ty_and_layout.size, cx)
Self::from_variant(Def::Primitive, None, (ty, layout), layout.size, cx)
}
FieldsShape::Array { .. } | FieldsShape::Union(_) => Err(Err::NotYetSupported),
}
@ -300,13 +297,13 @@ pub(crate) mod rustc {
///
/// Panics if `def` is not a struct definition.
fn from_struct(
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
def: AdtDef<'tcx>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
assert!(def.is_struct());
let def = Def::Adt(def);
Self::from_variant(def, None, ty_and_layout, ty_and_layout.size, cx)
Self::from_variant(def, None, (ty, layout), layout.size, cx)
}
/// Constructs a `Tree` from an enum.
@ -315,19 +312,18 @@ pub(crate) mod rustc {
///
/// Panics if `def` is not an enum definition.
fn from_enum(
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
def: AdtDef<'tcx>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
assert!(def.is_enum());
let layout = ty_and_layout.layout;
// Computes the variant of a given index.
let layout_of_variant = |index| {
let tag = cx.tcx.tag_for_variant((ty_and_layout.ty, index));
let tag = cx.tcx.tag_for_variant((cx.tcx.erase_regions(ty), index));
let variant_def = Def::Variant(def.variant(index));
let variant_ty_and_layout = ty_and_layout.for_variant(&cx, index);
Self::from_variant(variant_def, tag, variant_ty_and_layout, layout.size, cx)
let variant_layout = ty_variant(cx, (ty, layout), index);
Self::from_variant(variant_def, tag, (ty, variant_layout), layout.size, cx)
};
// We consider three kinds of enums, each demanding a different
@ -385,21 +381,20 @@ pub(crate) mod rustc {
fn from_variant(
def: Def<'tcx>,
tag: Option<ScalarInt>,
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
total_size: Size,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
// This constructor does not support non-`FieldsShape::Arbitrary`
// layouts.
let FieldsShape::Arbitrary { offsets, memory_index } = ty_and_layout.layout.fields()
else {
let FieldsShape::Arbitrary { offsets, memory_index } = layout.fields() else {
return Err(Err::NotYetSupported);
};
// When this function is invoked with enum variants,
// `ty_and_layout.size` does not encompass the entire size of the
// enum. We rely on `total_size` for this.
assert!(ty_and_layout.size <= total_size);
assert!(layout.size <= total_size);
let mut size = Size::ZERO;
let mut struct_tree = Self::def(def);
@ -412,17 +407,18 @@ pub(crate) mod rustc {
// Append the fields, in memory order, to the layout.
let inverse_memory_index = memory_index.invert_bijective_mapping();
for (memory_idx, field_idx) in inverse_memory_index.iter_enumerated() {
for (memory_idx, &field_idx) in inverse_memory_index.iter_enumerated() {
// Add interfield padding.
let padding_needed = offsets[*field_idx] - size;
let padding_needed = offsets[field_idx] - size;
let padding = Self::padding(padding_needed.bytes_usize());
let field_ty_and_layout = ty_and_layout.field(&cx, field_idx.as_usize());
let field_tree = Self::from_ty(field_ty_and_layout, cx)?;
let field_ty = ty_field(cx, (ty, layout), field_idx);
let field_layout = ty_layout(cx, field_ty);
let field_tree = Self::from_ty(field_ty, cx)?;
struct_tree = struct_tree.then(padding).then(field_tree);
size += padding_needed + field_ty_and_layout.size;
size += padding_needed + field_layout.size;
}
// Add trailing padding.
@ -457,28 +453,27 @@ pub(crate) mod rustc {
///
/// Panics if `def` is not a union definition.
fn from_union(
ty_and_layout: TyAndLayout<'tcx, Ty<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
def: AdtDef<'tcx>,
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
) -> Result<Self, Err> {
assert!(def.is_union());
let union_layout = ty_and_layout.layout;
// This constructor does not support non-`FieldsShape::Union`
// layouts. Fields of this shape are all placed at offset 0.
let FieldsShape::Union(fields) = union_layout.fields() else {
let FieldsShape::Union(fields) = layout.fields() else {
return Err(Err::NotYetSupported);
};
let fields = &def.non_enum_variant().fields;
let fields = fields.iter_enumerated().try_fold(
Self::uninhabited(),
|fields, (idx, ref field_def)| {
|fields, (idx, field_def)| {
let field_def = Def::Field(field_def);
let field_ty_and_layout = ty_and_layout.field(&cx, idx.as_usize());
let field = Self::from_ty(field_ty_and_layout, cx)?;
let trailing_padding_needed = union_layout.size - field_ty_and_layout.size;
let field_ty = ty_field(cx, (ty, layout), idx);
let field_layout = ty_layout(cx, field_ty);
let field = Self::from_ty(field_ty, cx)?;
let trailing_padding_needed = layout.size - field_layout.size;
let trailing_padding = Self::padding(trailing_padding_needed.bytes_usize());
let field_and_padding = field.then(trailing_padding);
Result::<Self, Err>::Ok(fields.or(field_and_padding))
@ -488,4 +483,44 @@ pub(crate) mod rustc {
Ok(Self::def(Def::Adt(def)).then(fields))
}
}
pub(crate) fn ty_layout<'tcx>(cx: LayoutCx<'tcx, TyCtxt<'tcx>>, ty: Ty<'tcx>) -> Layout<'tcx> {
crate::layout::rustc::layout_of(cx, ty).unwrap()
}
fn ty_field<'tcx>(
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
i: FieldIdx,
) -> Ty<'tcx> {
match ty.kind() {
ty::Adt(def, args) => {
match layout.variants {
Variants::Single { index } => {
let field = &def.variant(index).fields[i];
field.ty(cx.tcx, args)
}
// Discriminant field for enums (where applicable).
Variants::Multiple { tag, .. } => {
assert_eq!(i.as_usize(), 0);
ty::layout::PrimitiveExt::to_ty(&tag.primitive(), cx.tcx)
}
}
}
ty::Tuple(fields) => fields[i.as_usize()],
kind @ _ => unimplemented!(
"only a subset of `Ty::ty_and_layout_field`'s functionality is implemented. implementation needed for {:?}",
kind
),
}
}
fn ty_variant<'tcx>(
cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
(ty, layout): (Ty<'tcx>, Layout<'tcx>),
i: VariantIdx,
) -> Layout<'tcx> {
let ty = cx.tcx.erase_regions(ty);
TyAndLayout { ty, layout }.for_variant(&cx, i).layout
}
}

2
compiler/rustc_transmute/src/lib.rs
View File

@ -9,7 +9,7 @@ pub(crate) use rustc_data_structures::fx::{FxIndexMap as Map, FxIndexSet as Set}
pub mod layout;
mod maybe_transmutable;
#[derive(Default)]
#[derive(Copy, Clone, Debug, Default)]
pub struct Assume {
pub alignment: bool,
pub lifetimes: bool,

7
compiler/rustc_transmute/src/maybe_transmutable/mod.rs
View File

@ -30,7 +30,7 @@ where
// FIXME: Nix this cfg, so we can write unit tests independently of rustc
#[cfg(feature = "rustc")]
mod rustc {
use rustc_middle::ty::layout::{LayoutCx, LayoutOf};
use rustc_middle::ty::layout::LayoutCx;
use rustc_middle::ty::{ParamEnv, Ty, TyCtxt};
use super::*;
@ -45,10 +45,9 @@ mod rustc {
let layout_cx = LayoutCx { tcx: context, param_env: ParamEnv::reveal_all() };
let layout_of = |ty| {
layout_cx
.layout_of(ty)
crate::layout::rustc::layout_of(layout_cx, ty)
.map_err(|_| Err::NotYetSupported)
.and_then(|tl| Tree::from_ty(tl, layout_cx))
.and_then(|_| Tree::from_ty(ty, layout_cx))
};
// Convert `src` and `dst` from their rustc representations, to `Tree`-based

91
tests/ui/transmutability/references/accept_assume_lifetime_extension.rs Normal file
View File

@ -0,0 +1,91 @@
//@ check-pass
//! Accept lifetime extensions with `Assume::LIFETIMES`.
#![feature(transmutability, core_intrinsics)]
use std::mem::{Assume, BikeshedIntrinsicFrom};
unsafe fn transmute<Src, Dst>(src: Src) -> Dst
where
Dst: BikeshedIntrinsicFrom<Src, { Assume::SAFETY.and(Assume::LIFETIMES) }>,
{
core::intrinsics::transmute_unchecked(src)
}
mod bare {
use super::*;
fn extend_bare<'a>(src: &'a u8) -> &'static u8 {
unsafe { transmute(src) }
}
}
mod nested {
use super::*;
fn extend_nested<'a>(src: &'a &'a u8) -> &'a &'static u8 {
unsafe { transmute(src) }
}
}
mod tuple {
use super::*;
fn extend_unit<'a>(src: (&'a u8,)) -> (&'static u8,) {
unsafe { transmute(src) }
}
fn extend_pair<'a>(src: (&'a u8, u8)) -> (&'static u8, u8) {
unsafe { transmute(src) }
}
}
mod r#struct {
use super::*;
struct Struct<'a>(&'a u8);
fn extend_struct<'a>(src: Struct<'a>) -> Struct<'static> {
unsafe { transmute(src) }
}
}
mod r#enum {
use super::*;
enum Single<'a> {
A(&'a u8),
}
fn extend_single<'a>(src: Single<'a>) -> Single<'static> {
unsafe { transmute(src) }
}
enum Multi<'a> {
A(&'a u8),
B,
C,
}
fn extend_multi<'a>(src: Multi<'a>) -> Multi<'static> {
unsafe { transmute(src) }
}
}
mod hrtb {
use super::*;
fn call_extend_hrtb<'a>(src: &'a u8) -> &'static u8 {
unsafe { extend_hrtb(src) }
}
unsafe fn extend_hrtb<'a>(src: &'a u8) -> &'static u8
where
for<'b> &'b u8: BikeshedIntrinsicFrom<&'a u8, { Assume::LIFETIMES }>,
{
core::intrinsics::transmute_unchecked(src)
}
}
fn main() {}

68
tests/ui/transmutability/references/accept_unexercised_lifetime_extension.rs Normal file
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//@ check-pass
//! Accept lifetime extensions of un-exercised lifetimes.
#![feature(transmutability, core_intrinsics)]
use std::mem::{Assume, BikeshedIntrinsicFrom};
unsafe fn transmute<Src, Dst>(src: Src) -> Dst
where
Dst: BikeshedIntrinsicFrom<Src, { Assume::SAFETY }>,
{
core::intrinsics::transmute_unchecked(src)
}
enum Void {}
mod phantom {
use super::*;
use std::marker::PhantomData;
fn extend_bare<'a>(src: PhantomData<&'a u8>) -> PhantomData<&'static u8> {
unsafe { transmute(src) }
}
}
mod tuple {
use super::*;
fn extend_pair<'a>(src: (&'a u8, Void)) -> (&'static u8, Void) {
unsafe { transmute(src) }
}
}
mod r#struct {
use super::*;
struct Struct<'a>(&'a u8, Void);
fn extend_struct<'a>(src: Struct<'a>) -> Struct<'static> {
unsafe { transmute(src) }
}
}
mod r#enum {
use super::*;
enum Single<'a> {
A(&'a u8, Void),
}
fn extend_single<'a>(src: Single<'a>) -> Single<'static> {
unsafe { transmute(src) }
}
enum Multi<'a> {
A(&'a u8, Void),
B,
C,
}
fn extend_multi<'a>(src: Multi<'a>) -> Multi<'static> {
unsafe { transmute(src) }
}
}
fn main() {}

91
tests/ui/transmutability/references/reject_lifetime_extension.rs Normal file
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//@ check-fail
//! Reject lifetime extensions.
#![feature(transmutability, core_intrinsics)]
use std::mem::{Assume, BikeshedIntrinsicFrom};
unsafe fn transmute<Src, Dst>(src: Src) -> Dst
where
Dst: BikeshedIntrinsicFrom<Src, { Assume::SAFETY }>,
{
core::intrinsics::transmute_unchecked(src)
}
mod bare {
use super::*;
fn extend_bare<'a>(src: &'a u8) -> &'static u8 {
unsafe { transmute(src) } //~ ERROR lifetime may not live long enough
}
}
mod nested {
use super::*;
fn extend_nested<'a>(src: &'a &'a u8) -> &'a &'static u8 {
unsafe { transmute(src) } //~ ERROR lifetime may not live long enough
}
}
mod tuple {
use super::*;
fn extend_unit<'a>(src: (&'a u8,)) -> (&'static u8,) {
unsafe { transmute(src) } //~ ERROR lifetime may not live long enough
}
fn extend_pair<'a>(src: (&'a u8, u8)) -> (&'static u8, u8) {
unsafe { transmute(src) } //~ ERROR lifetime may not live long enough
}
}
mod r#struct {
use super::*;
struct Struct<'a>(&'a u8);
fn extend_struct<'a>(src: Struct<'a>) -> Struct<'static> {
unsafe { transmute(src) } //~ ERROR lifetime may not live long enough
}
}
mod r#enum {
use super::*;
enum Single<'a> {
A(&'a u8),
}
fn extend_single<'a>(src: Single<'a>) -> Single<'static> {
unsafe { transmute(src) } //~ ERROR lifetime may not live long enough
}
enum Multi<'a> {
A(&'a u8),
B,
C,
}
fn extend_multi<'a>(src: Multi<'a>) -> Multi<'static> {
unsafe { transmute(src) } //~ ERROR lifetime may not live long enough
}
}
mod hrtb {
use super::*;
fn call_extend_hrtb<'a>(src: &'a u8) -> &'static u8 {
unsafe { extend_hrtb(src) } //~ ERROR borrowed data escapes outside of function
}
unsafe fn extend_hrtb<'a>(src: &'a u8) -> &'static u8
where
for<'b> &'b u8: BikeshedIntrinsicFrom<&'a u8>,
{
core::intrinsics::transmute_unchecked(src)
}
}
fn main() {}

78
tests/ui/transmutability/references/reject_lifetime_extension.stderr Normal file
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error: lifetime may not live long enough
--> $DIR/reject_lifetime_extension.rs:20:18
|
LL | fn extend_bare<'a>(src: &'a u8) -> &'static u8 {
| -- lifetime `'a` defined here
LL | unsafe { transmute(src) }
| ^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
error: lifetime may not live long enough
--> $DIR/reject_lifetime_extension.rs:28:18
|
LL | fn extend_nested<'a>(src: &'a &'a u8) -> &'a &'static u8 {
| -- lifetime `'a` defined here
LL | unsafe { transmute(src) }
| ^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
error: lifetime may not live long enough
--> $DIR/reject_lifetime_extension.rs:36:18
|
LL | fn extend_unit<'a>(src: (&'a u8,)) -> (&'static u8,) {
| -- lifetime `'a` defined here
LL | unsafe { transmute(src) }
| ^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
error: lifetime may not live long enough
--> $DIR/reject_lifetime_extension.rs:40:18
|
LL | fn extend_pair<'a>(src: (&'a u8, u8)) -> (&'static u8, u8) {
| -- lifetime `'a` defined here
LL | unsafe { transmute(src) }
| ^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
error: lifetime may not live long enough
--> $DIR/reject_lifetime_extension.rs:50:18
|
LL | fn extend_struct<'a>(src: Struct<'a>) -> Struct<'static> {
| -- lifetime `'a` defined here
LL | unsafe { transmute(src) }
| ^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
error: lifetime may not live long enough
--> $DIR/reject_lifetime_extension.rs:62:18
|
LL | fn extend_single<'a>(src: Single<'a>) -> Single<'static> {
| -- lifetime `'a` defined here
LL | unsafe { transmute(src) }
| ^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
error: lifetime may not live long enough
--> $DIR/reject_lifetime_extension.rs:72:18
|
LL | fn extend_multi<'a>(src: Multi<'a>) -> Multi<'static> {
| -- lifetime `'a` defined here
LL | unsafe { transmute(src) }
| ^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
error[E0521]: borrowed data escapes outside of function
--> $DIR/reject_lifetime_extension.rs:80:18
|
LL | fn call_extend_hrtb<'a>(src: &'a u8) -> &'static u8 {
| -- --- `src` is a reference that is only valid in the function body
| |
| lifetime `'a` defined here
LL | unsafe { extend_hrtb(src) }
| ^^^^^^^^^^^^^^^^
| |
| `src` escapes the function body here
| argument requires that `'a` must outlive `'static`
|
note: due to current limitations in the borrow checker, this implies a `'static` lifetime
--> $DIR/reject_lifetime_extension.rs:85:25
|
LL | for<'b> &'b u8: BikeshedIntrinsicFrom<&'a u8>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 8 previous errors
For more information about this error, try `rustc --explain E0521`.