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Rollup merge of #129392 - compiler-errors:raw-ref-op-doesnt-diverge-but-more, r=lcnr

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Do not consider match/let/ref of place that evaluates to `!` to diverge, disallow coercions from them too

Fixes #117288.

This PR implements a heuristic which disables two things that are currently being performed on the HIR when we have **expressions that involve place-like expressions that point to `!`**. Specifically, it will (in certain cases explained below):

### (1.) Disable the `NeverToAny` coercion we implicitly insert for `!`.

Which fixes this inadvertent, sneaky unsoundness:

```
unsafe {
    let x: *const ! = &0 as *const u8 as *const !;
    let _: () = *x;
}
```

which is UB because currently rust emits an *implicit* NeverToAny coercion even though we really shouldn't be, since there's no read of the value pointed by `x`.

### (2.) Disable the logic which considers expression which evaluate to `!` to diverge, which affects the type returned by the containing block.

Which fixes this unsoundness:

```
fn make_up_a_value<T>() -> T {
    unsafe {
        let x: *const ! = &0 as *const u8 as *const !;
        let _ = *x;
    }
}
```

We disable these two operations **if** the expression is a place-like expression (locals, statics, field projections, index operations, and deref operations), and if the parent expression is either:
(1.) the LHS of an assignment
(2.) AddrOf
(3.) A match or let **unless** all of the *patterns consitute a read*, which is explained below:

And finally, a pattern currently is considered to constitute a read **unless** it is a wildcard, or an OR pattern. An OR pattern is considered to constitute a read if all of its subpatterns constitute a read, to remain as conservative as possible in cases like `_ | subpat` or `subpat | _`.

All other patterns are considered currently to constitute a read. Specifically, because `NeverToAny` is a coercion performed on a *value* and not a *place*, `Struct { .. }` on a `!` type must be a coercion currently, and we currently rely on this behavior to allow us to perform coercions like `let _: i32 = x;` where `x: !`.

This is already considered UB by [miri](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=daf3a2246433fe43fdc07d1389c276c9), but also means it does not affect the preexisting UB in this case:

```
let Struct { .. } = *never_ptr;
```

Even though it's likely up for debate since we're not actually reading any data out of the struct, it almost certainly causes inference changes which I do *NOT* want to fix in this PR.
This commit is contained in:
Matthias Krüger 2024-10-06 11:06:57 +02:00 committed by GitHub
commit 9aaebd481a
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GPG Key ID: B5690EEEBB952194
15 changed files with 634 additions and 32 deletions
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46
compiler/rustc_hir_typeck/src/coercion.rs
View File

@ -82,6 +82,11 @@ struct Coerce<'a, 'tcx> {
/// See #47489 and #48598
/// See docs on the "AllowTwoPhase" type for a more detailed discussion
allow_two_phase: AllowTwoPhase,
/// Whether we allow `NeverToAny` coercions. This is unsound if we're
/// coercing a place expression without it counting as a read in the MIR.
/// This is a side-effect of HIR not really having a great distinction
/// between places and values.
coerce_never: bool,
}
impl<'a, 'tcx> Deref for Coerce<'a, 'tcx> {
@ -125,8 +130,9 @@ fn new(
fcx: &'f FnCtxt<'f, 'tcx>,
cause: ObligationCause<'tcx>,
allow_two_phase: AllowTwoPhase,
coerce_never: bool,
) -> Self {
Coerce { fcx, cause, allow_two_phase, use_lub: false }
Coerce { fcx, cause, allow_two_phase, use_lub: false, coerce_never }
}
fn unify(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> InferResult<'tcx, Ty<'tcx>> {
@ -177,7 +183,12 @@ fn coerce(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
// Coercing from `!` to any type is allowed:
if a.is_never() {
return success(simple(Adjust::NeverToAny)(b), b, vec![]);
if self.coerce_never {
return success(simple(Adjust::NeverToAny)(b), b, vec![]);
} else {
// Otherwise the only coercion we can do is unification.
return self.unify_and(a, b, identity);
}
}
// Coercing *from* an unresolved inference variable means that
@ -1038,7 +1049,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
/// The expressions *must not* have any preexisting adjustments.
pub(crate) fn coerce(
&self,
expr: &hir::Expr<'_>,
expr: &'tcx hir::Expr<'tcx>,
expr_ty: Ty<'tcx>,
mut target: Ty<'tcx>,
allow_two_phase: AllowTwoPhase,
@ -1055,7 +1066,12 @@ pub(crate) fn coerce(
let cause =
cause.unwrap_or_else(|| self.cause(expr.span, ObligationCauseCode::ExprAssignable));
let coerce = Coerce::new(self, cause, allow_two_phase);
let coerce = Coerce::new(
self,
cause,
allow_two_phase,
self.expr_guaranteed_to_constitute_read_for_never(expr),
);
let ok = self.commit_if_ok(|_| coerce.coerce(source, target))?;
let (adjustments, _) = self.register_infer_ok_obligations(ok);
@ -1077,8 +1093,9 @@ pub(crate) fn can_coerce(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> bool {
debug!("coercion::can_with_predicates({:?} -> {:?})", source, target);
let cause = self.cause(DUMMY_SP, ObligationCauseCode::ExprAssignable);
// We don't ever need two-phase here since we throw out the result of the coercion
let coerce = Coerce::new(self, cause, AllowTwoPhase::No);
// We don't ever need two-phase here since we throw out the result of the coercion.
// We also just always set `coerce_never` to true, since this is a heuristic.
let coerce = Coerce::new(self, cause, AllowTwoPhase::No, true);
self.probe(|_| {
let Ok(ok) = coerce.coerce(source, target) else {
return false;
@ -1090,12 +1107,16 @@ pub(crate) fn can_coerce(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> bool {
}
/// Given a type and a target type, this function will calculate and return
/// how many dereference steps needed to achieve `expr_ty <: target`. If
/// how many dereference steps needed to coerce `expr_ty` to `target`. If
/// it's not possible, return `None`.
pub(crate) fn deref_steps(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> Option<usize> {
pub(crate) fn deref_steps_for_suggestion(
&self,
expr_ty: Ty<'tcx>,
target: Ty<'tcx>,
) -> Option<usize> {
let cause = self.cause(DUMMY_SP, ObligationCauseCode::ExprAssignable);
// We don't ever need two-phase here since we throw out the result of the coercion
let coerce = Coerce::new(self, cause, AllowTwoPhase::No);
// We don't ever need two-phase here since we throw out the result of the coercion.
let coerce = Coerce::new(self, cause, AllowTwoPhase::No, true);
coerce
.autoderef(DUMMY_SP, expr_ty)
.find_map(|(ty, steps)| self.probe(|_| coerce.unify(ty, target)).ok().map(|_| steps))
@ -1252,7 +1273,10 @@ fn try_find_coercion_lub<E>(
// probably aren't processing function arguments here and even if we were,
// they're going to get autorefed again anyway and we can apply 2-phase borrows
// at that time.
let mut coerce = Coerce::new(self, cause.clone(), AllowTwoPhase::No);
//
// NOTE: we set `coerce_never` to `true` here because coercion LUBs only
// operate on values and not places, so a never coercion is valid.
let mut coerce = Coerce::new(self, cause.clone(), AllowTwoPhase::No, true);
coerce.use_lub = true;
// First try to coerce the new expression to the type of the previous ones,

191
compiler/rustc_hir_typeck/src/expr.rs
View File

@ -1,3 +1,6 @@
// ignore-tidy-filelength
// FIXME: we should move the field error reporting code somewhere else.
//! Type checking expressions.
//!
//! See [`rustc_hir_analysis::check`] for more context on type checking in general.
@ -62,7 +65,7 @@ pub(crate) fn check_expr_has_type_or_error(
// While we don't allow *arbitrary* coercions here, we *do* allow
// coercions from ! to `expected`.
if ty.is_never() {
if ty.is_never() && self.expr_guaranteed_to_constitute_read_for_never(expr) {
if let Some(_) = self.typeck_results.borrow().adjustments().get(expr.hir_id) {
let reported = self.dcx().span_delayed_bug(
expr.span,
@ -238,8 +241,11 @@ pub(super) fn check_expr_with_expectation_and_args(
_ => self.warn_if_unreachable(expr.hir_id, expr.span, "expression"),
}
// Any expression that produces a value of type `!` must have diverged
if ty.is_never() {
// Any expression that produces a value of type `!` must have diverged,
// unless it's a place expression that isn't being read from, in which case
// diverging would be unsound since we may never actually read the `!`.
// e.g. `let _ = *never_ptr;` with `never_ptr: *const !`.
if ty.is_never() && self.expr_guaranteed_to_constitute_read_for_never(expr) {
self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
}
@ -257,6 +263,185 @@ pub(super) fn check_expr_with_expectation_and_args(
ty
}
/// Whether this expression constitutes a read of value of the type that
/// it evaluates to.
///
/// This is used to determine if we should consider the block to diverge
/// if the expression evaluates to `!`, and if we should insert a `NeverToAny`
/// coercion for values of type `!`.
///
/// This function generally returns `false` if the expression is a place
/// expression and the *parent* expression is the scrutinee of a match or
/// the pointee of an `&` addr-of expression, since both of those parent
/// expressions take a *place* and not a value.
pub(super) fn expr_guaranteed_to_constitute_read_for_never(
&self,
expr: &'tcx hir::Expr<'tcx>,
) -> bool {
// We only care about place exprs. Anything else returns an immediate
// which would constitute a read. We don't care about distinguishing
// "syntactic" place exprs since if the base of a field projection is
// not a place then it would've been UB to read from it anyways since
// that constitutes a read.
if !expr.is_syntactic_place_expr() {
return true;
}
let parent_node = self.tcx.parent_hir_node(expr.hir_id);
match parent_node {
hir::Node::Expr(parent_expr) => {
match parent_expr.kind {
// Addr-of, field projections, and LHS of assignment don't constitute reads.
// Assignment does call `drop_in_place`, though, but its safety
// requirements are not the same.
ExprKind::AddrOf(..) | hir::ExprKind::Field(..) => false,
ExprKind::Assign(lhs, _, _) => {
// Only the LHS does not constitute a read
expr.hir_id != lhs.hir_id
}
// See note on `PatKind::Or` below for why this is `all`.
ExprKind::Match(scrutinee, arms, _) => {
assert_eq!(scrutinee.hir_id, expr.hir_id);
arms.iter()
.all(|arm| self.pat_guaranteed_to_constitute_read_for_never(arm.pat))
}
ExprKind::Let(hir::LetExpr { init, pat, .. }) => {
assert_eq!(init.hir_id, expr.hir_id);
self.pat_guaranteed_to_constitute_read_for_never(*pat)
}
// Any expression child of these expressions constitute reads.
ExprKind::Array(_)
| ExprKind::Call(_, _)
| ExprKind::MethodCall(_, _, _, _)
| ExprKind::Tup(_)
| ExprKind::Binary(_, _, _)
| ExprKind::Unary(_, _)
| ExprKind::Cast(_, _)
| ExprKind::Type(_, _)
| ExprKind::DropTemps(_)
| ExprKind::If(_, _, _)
| ExprKind::Closure(_)
| ExprKind::Block(_, _)
| ExprKind::AssignOp(_, _, _)
| ExprKind::Index(_, _, _)
| ExprKind::Break(_, _)
| ExprKind::Ret(_)
| ExprKind::Become(_)
| ExprKind::InlineAsm(_)
| ExprKind::Struct(_, _, _)
| ExprKind::Repeat(_, _)
| ExprKind::Yield(_, _) => true,
// These expressions have no (direct) sub-exprs.
ExprKind::ConstBlock(_)
| ExprKind::Loop(_, _, _, _)
| ExprKind::Lit(_)
| ExprKind::Path(_)
| ExprKind::Continue(_)
| ExprKind::OffsetOf(_, _)
| ExprKind::Err(_) => unreachable!("no sub-expr expected for {:?}", expr.kind),
}
}
// If we have a subpattern that performs a read, we want to consider this
// to diverge for compatibility to support something like `let x: () = *never_ptr;`.
hir::Node::LetStmt(hir::LetStmt { init: Some(target), pat, .. }) => {
assert_eq!(target.hir_id, expr.hir_id);
self.pat_guaranteed_to_constitute_read_for_never(*pat)
}
// These nodes (if they have a sub-expr) do constitute a read.
hir::Node::Block(_)
| hir::Node::Arm(_)
| hir::Node::ExprField(_)
| hir::Node::AnonConst(_)
| hir::Node::ConstBlock(_)
| hir::Node::ConstArg(_)
| hir::Node::Stmt(_)
| hir::Node::Item(hir::Item {
kind: hir::ItemKind::Const(..) | hir::ItemKind::Static(..),
..
})
| hir::Node::TraitItem(hir::TraitItem {
kind: hir::TraitItemKind::Const(..), ..
})
| hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Const(..), .. }) => true,
// These nodes do not have direct sub-exprs.
hir::Node::Param(_)
| hir::Node::Item(_)
| hir::Node::ForeignItem(_)
| hir::Node::TraitItem(_)
| hir::Node::ImplItem(_)
| hir::Node::Variant(_)
| hir::Node::Field(_)
| hir::Node::PathSegment(_)
| hir::Node::Ty(_)
| hir::Node::AssocItemConstraint(_)
| hir::Node::TraitRef(_)
| hir::Node::Pat(_)
| hir::Node::PatField(_)
| hir::Node::LetStmt(_)
| hir::Node::Synthetic
| hir::Node::Err(_)
| hir::Node::Ctor(_)
| hir::Node::Lifetime(_)
| hir::Node::GenericParam(_)
| hir::Node::Crate(_)
| hir::Node::Infer(_)
| hir::Node::WhereBoundPredicate(_)
| hir::Node::ArrayLenInfer(_)
| hir::Node::PreciseCapturingNonLifetimeArg(_)
| hir::Node::OpaqueTy(_) => {
unreachable!("no sub-expr expected for {parent_node:?}")
}
}
}
/// Whether this pattern constitutes a read of value of the scrutinee that
/// it is matching against. This is used to determine whether we should
/// perform `NeverToAny` coercions.
///
/// See above for the nuances of what happens when this returns true.
pub(super) fn pat_guaranteed_to_constitute_read_for_never(&self, pat: &hir::Pat<'_>) -> bool {
match pat.kind {
// Does not constitute a read.
hir::PatKind::Wild => false,
// This is unnecessarily restrictive when the pattern that doesn't
// constitute a read is unreachable.
//
// For example `match *never_ptr { value => {}, _ => {} }` or
// `match *never_ptr { _ if false => {}, value => {} }`.
//
// It is however fine to be restrictive here; only returning `true`
// can lead to unsoundness.
hir::PatKind::Or(subpats) => {
subpats.iter().all(|pat| self.pat_guaranteed_to_constitute_read_for_never(pat))
}
// Does constitute a read, since it is equivalent to a discriminant read.
hir::PatKind::Never => true,
// All of these constitute a read, or match on something that isn't `!`,
// which would require a `NeverToAny` coercion.
hir::PatKind::Binding(_, _, _, _)
| hir::PatKind::Struct(_, _, _)
| hir::PatKind::TupleStruct(_, _, _)
| hir::PatKind::Path(_)
| hir::PatKind::Tuple(_, _)
| hir::PatKind::Box(_)
| hir::PatKind::Ref(_, _)
| hir::PatKind::Deref(_)
| hir::PatKind::Lit(_)
| hir::PatKind::Range(_, _, _)
| hir::PatKind::Slice(_, _, _)
| hir::PatKind::Err(_) => true,
}
}
#[instrument(skip(self, expr), level = "debug")]
fn check_expr_kind(
&self,

6
compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
View File

@ -2608,7 +2608,7 @@ pub(crate) fn suggest_deref_or_ref(
}
if let hir::ExprKind::Unary(hir::UnOp::Deref, inner) = expr.kind
&& let Some(1) = self.deref_steps(expected, checked_ty)
&& let Some(1) = self.deref_steps_for_suggestion(expected, checked_ty)
{
// We have `*&T`, check if what was expected was `&T`.
// If so, we may want to suggest removing a `*`.
@ -2738,7 +2738,7 @@ pub(crate) fn suggest_deref_or_ref(
}
}
(_, &ty::RawPtr(ty_b, mutbl_b), &ty::Ref(_, ty_a, mutbl_a)) => {
if let Some(steps) = self.deref_steps(ty_a, ty_b)
if let Some(steps) = self.deref_steps_for_suggestion(ty_a, ty_b)
// Only suggest valid if dereferencing needed.
&& steps > 0
// The pointer type implements `Copy` trait so the suggestion is always valid.
@ -2782,7 +2782,7 @@ pub(crate) fn suggest_deref_or_ref(
}
}
_ if sp == expr.span => {
if let Some(mut steps) = self.deref_steps(checked_ty, expected) {
if let Some(mut steps) = self.deref_steps_for_suggestion(checked_ty, expected) {
let mut expr = expr.peel_blocks();
let mut prefix_span = expr.span.shrink_to_lo();
let mut remove = String::new();

51
src/tools/miri/tests/pass/underscore_pattern.rs
View File

@ -1,5 +1,7 @@
// Various tests ensuring that underscore patterns really just construct the place, but don't check its contents.
#![feature(strict_provenance)]
#![feature(never_type)]
use std::ptr;
fn main() {
@ -9,6 +11,7 @@ fn main() {
invalid_let();
dangling_let_type_annotation();
invalid_let_type_annotation();
never();
}
fn dangling_match() {
@ -34,6 +37,13 @@ union Uninit<T: Copy> {
_ => {}
}
}
unsafe {
let x: Uninit<!> = Uninit { uninit: () };
match x.value {
_ => {}
}
}
}
fn dangling_let() {
@ -41,6 +51,11 @@ fn dangling_let() {
let ptr = ptr::without_provenance::<bool>(0x40);
let _ = *ptr;
}
unsafe {
let ptr = ptr::without_provenance::<!>(0x40);
let _ = *ptr;
}
}
fn invalid_let() {
@ -49,6 +64,12 @@ fn invalid_let() {
let ptr = ptr::addr_of!(val).cast::<bool>();
let _ = *ptr;
}
unsafe {
let val = 3u8;
let ptr = ptr::addr_of!(val).cast::<!>();
let _ = *ptr;
}
}
// Adding a type annotation used to change how MIR is generated, make sure we cover both cases.
@ -57,6 +78,11 @@ fn dangling_let_type_annotation() {
let ptr = ptr::without_provenance::<bool>(0x40);
let _: bool = *ptr;
}
unsafe {
let ptr = ptr::without_provenance::<!>(0x40);
let _: ! = *ptr;
}
}
fn invalid_let_type_annotation() {
@ -65,7 +91,28 @@ fn invalid_let_type_annotation() {
let ptr = ptr::addr_of!(val).cast::<bool>();
let _: bool = *ptr;
}
unsafe {
let val = 3u8;
let ptr = ptr::addr_of!(val).cast::<!>();
let _: ! = *ptr;
}
}
// FIXME: we should also test `!`, not just `bool` -- but that s currently buggy:
// https://github.com/rust-lang/rust/issues/117288
// Regression test from <https://github.com/rust-lang/rust/issues/117288>.
fn never() {
unsafe {
let x = 3u8;
let x: *const ! = &x as *const u8 as *const _;
let _: ! = *x;
}
// Without a type annotation, make sure we don't implicitly coerce `!` to `()`
// when we do the noop `*x` (as that would require a `!` *value*, creating
// which is UB).
unsafe {
let x = 3u8;
let x: *const ! = &x as *const u8 as *const _;
let _ = *x;
}
}

3
tests/mir-opt/uninhabited_enum.process_never.SimplifyLocals-final.after.mir
View File

@ -3,9 +3,8 @@
fn process_never(_1: *const !) -> () {
debug input => _1;
let mut _0: ();
let _2: &!;
scope 1 {
debug _input => _2;
debug _input => const ();
}
bb0: {

2
tests/mir-opt/uninhabited_enum.process_void.SimplifyLocals-final.after.mir
View File

@ -4,7 +4,7 @@ fn process_void(_1: *const Void) -> () {
debug input => _1;
let mut _0: ();
scope 1 {
debug _input => _1;
debug _input => const ZeroSized: Void;
}
bb0: {

5
tests/mir-opt/uninhabited_enum.rs
View File

@ -1,18 +1,19 @@
// skip-filecheck
#![feature(never_type)]
#[derive(Copy, Clone)]
pub enum Void {}
// EMIT_MIR uninhabited_enum.process_never.SimplifyLocals-final.after.mir
#[no_mangle]
pub fn process_never(input: *const !) {
let _input = unsafe { &*input };
let _input = unsafe { *input };
}
// EMIT_MIR uninhabited_enum.process_void.SimplifyLocals-final.after.mir
#[no_mangle]
pub fn process_void(input: *const Void) {
let _input = unsafe { &*input };
let _input = unsafe { *input };
// In the future, this should end with `unreachable`, but we currently only do
// unreachability analysis for `!`.
}

49
tests/mir-opt/uninhabited_not_read.main.SimplifyLocals-final.after.mir Normal file
View File

@ -0,0 +1,49 @@
// MIR for `main` after SimplifyLocals-final
fn main() -> () {
let mut _0: ();
let _1: u8;
let mut _2: *const !;
let mut _3: *const u8;
let _4: u8;
let mut _5: *const !;
let mut _6: *const u8;
scope 1 {
debug x => _1;
scope 2 {
debug x => _2;
scope 3 {
}
}
}
scope 4 {
debug x => _4;
scope 5 {
debug x => _5;
scope 6 {
}
}
}
bb0: {
StorageLive(_1);
_1 = const 3_u8;
StorageLive(_2);
StorageLive(_3);
_3 = &raw const _1;
_2 = move _3 as *const ! (PtrToPtr);
StorageDead(_3);
StorageDead(_2);
StorageDead(_1);
StorageLive(_4);
_4 = const 3_u8;
StorageLive(_5);
StorageLive(_6);
_6 = &raw const _4;
_5 = move _6 as *const ! (PtrToPtr);
StorageDead(_6);
StorageDead(_5);
StorageDead(_4);
return;
}
}

26
tests/mir-opt/uninhabited_not_read.rs Normal file
View File

@ -0,0 +1,26 @@
// skip-filecheck
//@ edition: 2021
// In ed 2021 and below, we don't fallback `!` to `()`.
// This would introduce a `! -> ()` coercion which would
// be UB if we didn't disallow this explicitly.
#![feature(never_type)]
// EMIT_MIR uninhabited_not_read.main.SimplifyLocals-final.after.mir
fn main() {
// With a type annotation
unsafe {
let x = 3u8;
let x: *const ! = &x as *const u8 as *const _;
let _: ! = *x;
}
// Without a type annotation, make sure we don't implicitly coerce `!` to `()`
// when we do the noop `*x`.
unsafe {
let x = 3u8;
let x: *const ! = &x as *const u8 as *const _;
let _ = *x;
}
}

6
tests/ui/closures/2229_closure_analysis/match/pattern-matching-should-fail.stderr
View File

@ -7,14 +7,12 @@ LL | let c1 = || match x { };
| ^ `x` used here but it isn't initialized
error[E0381]: used binding `x` isn't initialized
--> $DIR/pattern-matching-should-fail.rs:15:14
--> $DIR/pattern-matching-should-fail.rs:15:23
|
LL | let x: !;
| - binding declared here but left uninitialized
LL | let c2 = || match x { _ => () };
| ^^ - borrow occurs due to use in closure
| |
| `x` used here but it isn't initialized
| ^ `x` used here but it isn't initialized
error[E0381]: used binding `variant` isn't initialized
--> $DIR/pattern-matching-should-fail.rs:27:13

74
tests/ui/never_type/diverging-place-match.rs Normal file
View File

@ -0,0 +1,74 @@
#![feature(never_type)]
fn not_a_read() -> ! {
unsafe {
//~^ ERROR mismatched types
let x: *const ! = 0 as _;
let _: ! = *x;
// Since `*x` "diverges" in HIR, but doesn't count as a read in MIR, this
// is unsound since we act as if it diverges but it doesn't.
}
}
fn not_a_read_implicit() -> ! {
unsafe {
//~^ ERROR mismatched types
let x: *const ! = 0 as _;
let _ = *x;
}
}
fn not_a_read_guide_coercion() -> ! {
unsafe {
//~^ ERROR mismatched types
let x: *const ! = 0 as _;
let _: () = *x;
//~^ ERROR mismatched types
}
}
fn empty_match() -> ! {
unsafe {
//~^ ERROR mismatched types
let x: *const ! = 0 as _;
match *x { _ => {} };
}
}
fn field_projection() -> ! {
unsafe {
//~^ ERROR mismatched types
let x: *const (!, ()) = 0 as _;
let _ = (*x).0;
// ^ I think this is still UB, but because of the inbounds projection.
}
}
fn covered_arm() -> ! {
unsafe {
//~^ ERROR mismatched types
let x: *const ! = 0 as _;
let (_ | 1i32) = *x;
//~^ ERROR mismatched types
}
}
// FIXME: This *could* be considered a read of `!`, but we're not that sophisticated..
fn uncovered_arm() -> ! {
unsafe {
//~^ ERROR mismatched types
let x: *const ! = 0 as _;
let (1i32 | _) = *x;
//~^ ERROR mismatched types
}
}
fn coerce_ref_binding() -> ! {
unsafe {
let x: *const ! = 0 as _;
let ref _x: () = *x;
//~^ ERROR mismatched types
}
}
fn main() {}

142
tests/ui/never_type/diverging-place-match.stderr Normal file
View File

@ -0,0 +1,142 @@
error[E0308]: mismatched types
--> $DIR/diverging-place-match.rs:4:5
|
LL | / unsafe {
LL | |
LL | | let x: *const ! = 0 as _;
LL | | let _: ! = *x;
LL | | // Since `*x` "diverges" in HIR, but doesn't count as a read in MIR, this
LL | | // is unsound since we act as if it diverges but it doesn't.
LL | | }
| |_____^ expected `!`, found `()`
|
= note: expected type `!`
found unit type `()`
error[E0308]: mismatched types
--> $DIR/diverging-place-match.rs:14:5
|
LL | / unsafe {
LL | |
LL | | let x: *const ! = 0 as _;
LL | | let _ = *x;
LL | | }
| |_____^ expected `!`, found `()`
|
= note: expected type `!`
found unit type `()`
error[E0308]: mismatched types
--> $DIR/diverging-place-match.rs:25:21
|
LL | let _: () = *x;
| -- ^^ expected `()`, found `!`
| |
| expected due to this
|
= note: expected unit type `()`
found type `!`
error[E0308]: mismatched types
--> $DIR/diverging-place-match.rs:22:5
|
LL | / unsafe {
LL | |
LL | | let x: *const ! = 0 as _;
LL | | let _: () = *x;
LL | |
LL | | }
| |_____^ expected `!`, found `()`
|
= note: expected type `!`
found unit type `()`
error[E0308]: mismatched types
--> $DIR/diverging-place-match.rs:31:5
|
LL | / unsafe {
LL | |
LL | | let x: *const ! = 0 as _;
LL | | match *x { _ => {} };
LL | | }
| |_____^ expected `!`, found `()`
|
= note: expected type `!`
found unit type `()`
error[E0308]: mismatched types
--> $DIR/diverging-place-match.rs:39:5
|
LL | / unsafe {
LL | |
LL | | let x: *const (!, ()) = 0 as _;
LL | | let _ = (*x).0;
LL | | // ^ I think this is still UB, but because of the inbounds projection.
LL | | }
| |_____^ expected `!`, found `()`
|
= note: expected type `!`
found unit type `()`
error[E0308]: mismatched types
--> $DIR/diverging-place-match.rs:51:18
|
LL | let (_ | 1i32) = *x;
| ^^^^ -- this expression has type `!`
| |
| expected `!`, found `i32`
|
= note: expected type `!`
found type `i32`
error[E0308]: mismatched types
--> $DIR/diverging-place-match.rs:48:5
|
LL | / unsafe {
LL | |
LL | | let x: *const ! = 0 as _;
LL | | let (_ | 1i32) = *x;
LL | |
LL | | }
| |_____^ expected `!`, found `()`
|
= note: expected type `!`
found unit type `()`
error[E0308]: mismatched types
--> $DIR/diverging-place-match.rs:61:14
|
LL | let (1i32 | _) = *x;
| ^^^^ -- this expression has type `!`
| |
| expected `!`, found `i32`
|
= note: expected type `!`
found type `i32`
error[E0308]: mismatched types
--> $DIR/diverging-place-match.rs:58:5
|
LL | / unsafe {
LL | |
LL | | let x: *const ! = 0 as _;
LL | | let (1i32 | _) = *x;
LL | |
LL | | }
| |_____^ expected `!`, found `()`
|
= note: expected type `!`
found unit type `()`
error[E0308]: mismatched types
--> $DIR/diverging-place-match.rs:69:26
|
LL | let ref _x: () = *x;
| ^^ expected `()`, found `!`
|
= note: expected unit type `()`
found type `!`
error: aborting due to 11 previous errors
For more information about this error, try `rustc --explain E0308`.

22
tests/ui/raw-ref-op/never-place-isnt-diverging.rs Normal file
View File

@ -0,0 +1,22 @@
#![feature(never_type)]
fn make_up_a_value<T>() -> T {
unsafe {
//~^ ERROR mismatched types
let x: *const ! = 0 as _;
&raw const *x;
// Since `*x` is `!`, HIR typeck used to think that it diverges
// and allowed the block to coerce to any value, leading to UB.
}
}
fn make_up_a_pointer<T>() -> *const T {
unsafe {
let x: *const ! = 0 as _;
&raw const *x
//~^ ERROR mismatched types
}
}
fn main() {}

34
tests/ui/raw-ref-op/never-place-isnt-diverging.stderr Normal file
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@ -0,0 +1,34 @@
error[E0308]: mismatched types
--> $DIR/never-place-isnt-diverging.rs:4:5
|
LL | fn make_up_a_value<T>() -> T {
| - expected this type parameter
LL | / unsafe {
LL | |
LL | | let x: *const ! = 0 as _;
LL | | &raw const *x;
LL | | // Since `*x` is `!`, HIR typeck used to think that it diverges
LL | | // and allowed the block to coerce to any value, leading to UB.
LL | | }
| |_____^ expected type parameter `T`, found `()`
|
= note: expected type parameter `T`
found unit type `()`
error[E0308]: mismatched types
--> $DIR/never-place-isnt-diverging.rs:17:9
|
LL | fn make_up_a_pointer<T>() -> *const T {
| - -------- expected `*const T` because of return type
| |
| expected this type parameter
...
LL | &raw const *x
| ^^^^^^^^^^^^^ expected `*const T`, found `*const !`
|
= note: expected raw pointer `*const T`
found raw pointer `*const !`
error: aborting due to 2 previous errors
For more information about this error, try `rustc --explain E0308`.

9
tests/ui/reachable/expr_assign.stderr
View File

@ -14,12 +14,13 @@ LL | #![deny(unreachable_code)]
| ^^^^^^^^^^^^^^^^
error: unreachable expression
--> $DIR/expr_assign.rs:20:14
--> $DIR/expr_assign.rs:20:9
|
LL | *p = return;
| -- ^^^^^^ unreachable expression
| |
| any code following this expression is unreachable
| ^^^^^------
| | |
| | any code following this expression is unreachable
| unreachable expression
error: unreachable expression
--> $DIR/expr_assign.rs:26:15