Skip to content

Commit 2c70eb4

Browse files
borsbors
committed
Auto merge of #129199 - RalfJung:writes_through_immutable_pointer, r=<try>
make writes_through_immutable_pointer a hard error This turns the lint added in #118324 into a hard error. This has been reported in cargo's future-compat reports since Rust 1.76 (released in February). Given that const_mut_refs is still unstable, it should be impossible to even hit this error on stable: we did accidentally stabilize some functions that can cause this error, but that got reverted in #117905. Still, let's do a crater run just to be sure. Given that this should only affect unstable code, I don't think it needs an FCP, but let's Cc `@rust-lang/lang` anyway -- any objection to making this unambiguous UB into a hard error during const-eval? This can be viewed as part of #129195 which is already nominated for discussion.
2 parents 426a60a + 8b642a1 commit 2c70eb4

File tree

7 files changed

+23
-102
lines changed

7 files changed

+23
-102
lines changed

‎compiler/rustc_const_eval/src/const_eval/error.rs

+7-1
Original file line numberDiff line numberDiff line change
@@ -22,6 +22,7 @@ pub enum ConstEvalErrKind {
2222
RecursiveStatic,
2323
AssertFailure(AssertKind<ConstInt>),
2424
Panic { msg: Symbol, line: u32, col: u32, file: Symbol },
25+
WriteThroughImmutablePointer,
2526
}
2627

2728
impl MachineStopType for ConstEvalErrKind {
@@ -35,12 +36,16 @@ impl MachineStopType for ConstEvalErrKind {
3536
Panic { .. } => const_eval_panic,
3637
RecursiveStatic => const_eval_recursive_static,
3738
AssertFailure(x) => x.diagnostic_message(),
39+
WriteThroughImmutablePointer => const_eval_write_through_immutable_pointer,
3840
}
3941
}
4042
fn add_args(self: Box<Self>, adder: &mut dyn FnMut(DiagArgName, DiagArgValue)) {
4143
use ConstEvalErrKind::*;
4244
match *self {
43-
RecursiveStatic | ConstAccessesMutGlobal | ModifiedGlobal => {}
45+
RecursiveStatic
46+
| ConstAccessesMutGlobal
47+
| ModifiedGlobal
48+
| WriteThroughImmutablePointer => {}
4449
AssertFailure(kind) => kind.add_args(adder),
4550
Panic { msg, line, col, file } => {
4651
adder("msg".into(), msg.into_diag_arg());
@@ -159,6 +164,7 @@ where
159164

160165
/// Emit a lint from a const-eval situation, with a backtrace.
161166
// Even if this is unused, please don't remove it -- chances are we will need to emit a lint during const-eval again in the future!
167+
#[allow(unused)]
162168
pub(super) fn lint<'tcx, L>(
163169
tcx: TyCtxtAt<'tcx>,
164170
machine: &CompileTimeMachine<'tcx>,

‎compiler/rustc_const_eval/src/const_eval/machine.rs

+3-6
Original file line numberDiff line numberDiff line change
@@ -12,7 +12,6 @@ use rustc_middle::query::TyCtxtAt;
1212
use rustc_middle::ty::layout::{FnAbiOf, TyAndLayout};
1313
use rustc_middle::ty::{self, TyCtxt};
1414
use rustc_middle::{bug, mir};
15-
use rustc_session::lint::builtin::WRITES_THROUGH_IMMUTABLE_POINTER;
1615
use rustc_span::symbol::{sym, Symbol};
1716
use rustc_span::Span;
1817
use rustc_target::abi::{Align, Size};
@@ -729,8 +728,8 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
729728
}
730729

731730
fn before_memory_write(
732-
tcx: TyCtxtAt<'tcx>,
733-
machine: &mut Self,
731+
_tcx: TyCtxtAt<'tcx>,
732+
_machine: &mut Self,
734733
_alloc_extra: &mut Self::AllocExtra,
735734
(_alloc_id, immutable): (AllocId, bool),
736735
range: AllocRange,
@@ -741,9 +740,7 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
741740
}
742741
// Reject writes through immutable pointers.
743742
if immutable {
744-
super::lint(tcx, machine, WRITES_THROUGH_IMMUTABLE_POINTER, |frames| {
745-
crate::errors::WriteThroughImmutablePointer { frames }
746-
});
743+
return Err(ConstEvalErrKind::WriteThroughImmutablePointer.into());
747744
}
748745
// Everything else is fine.
749746
Ok(())

‎compiler/rustc_const_eval/src/errors.rs

-7
Original file line numberDiff line numberDiff line change
@@ -407,13 +407,6 @@ pub struct ConstEvalError {
407407
pub frame_notes: Vec<FrameNote>,
408408
}
409409

410-
#[derive(LintDiagnostic)]
411-
#[diag(const_eval_write_through_immutable_pointer)]
412-
pub struct WriteThroughImmutablePointer {
413-
#[subdiagnostic]
414-
pub frames: Vec<FrameNote>,
415-
}
416-
417410
#[derive(Diagnostic)]
418411
#[diag(const_eval_nullary_intrinsic_fail)]
419412
pub struct NullaryIntrinsicError {

‎compiler/rustc_lint/src/lib.rs

+2-1
Original file line numberDiff line numberDiff line change
@@ -569,7 +569,8 @@ fn register_builtins(store: &mut LintStore) {
569569
"byte_slice_in_packed_struct_with_derive",
570570
"converted into hard error, see issue #107457 \
571571
<https://github.com/rust-lang/rust/issues/107457> for more information",
572-
)
572+
);
573+
store.register_removed("writes_through_immutable_pointer", "converted into hard error");
573574
}
574575

575576
fn register_internals(store: &mut LintStore) {

‎compiler/rustc_lint_defs/src/builtin.rs

-35
Original file line numberDiff line numberDiff line change
@@ -142,7 +142,6 @@ declare_lint_pass! {
142142
USELESS_DEPRECATED,
143143
WARNINGS,
144144
WASM_C_ABI,
145-
WRITES_THROUGH_IMMUTABLE_POINTER,
146145
// tidy-alphabetical-end
147146
]
148147
}
@@ -4696,40 +4695,6 @@ declare_lint! {
46964695
};
46974696
}
46984697

4699-
declare_lint! {
4700-
/// The `writes_through_immutable_pointer` lint detects writes through pointers derived from
4701-
/// shared references.
4702-
///
4703-
/// ### Example
4704-
///
4705-
/// ```rust,compile_fail
4706-
/// #![feature(const_mut_refs)]
4707-
/// const WRITE_AFTER_CAST: () = unsafe {
4708-
/// let mut x = 0;
4709-
/// let ptr = &x as *const i32 as *mut i32;
4710-
/// *ptr = 0;
4711-
/// };
4712-
/// ```
4713-
///
4714-
/// {{produces}}
4715-
///
4716-
/// ### Explanation
4717-
///
4718-
/// Shared references are immutable (when there is no `UnsafeCell` involved),
4719-
/// and writing through them or through pointers derived from them is Undefined Behavior.
4720-
/// The compiler recently learned to detect such Undefined Behavior during compile-time
4721-
/// evaluation, and in the future this will raise a hard error.
4722-
///
4723-
/// [future-incompatible]: ../index.md#future-incompatible-lints
4724-
pub WRITES_THROUGH_IMMUTABLE_POINTER,
4725-
Warn,
4726-
"shared references are immutable, and pointers derived from them must not be written to",
4727-
@future_incompatible = FutureIncompatibleInfo {
4728-
reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
4729-
reference: "issue #X <https://github.com/rust-lang/rust/issues/X>",
4730-
};
4731-
}
4732-
47334698
declare_lint! {
47344699
/// The `private_macro_use` lint detects private macros that are imported
47354700
/// with `#[macro_use]`.

‎tests/ui/consts/const-eval/ub-write-through-immutable.rs

+4-5
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,5 @@
11
//! Ensure we catch UB due to writing through a shared reference.
22
#![feature(const_mut_refs, const_refs_to_cell)]
3-
#![deny(writes_through_immutable_pointer)]
43
#![allow(invalid_reference_casting)]
54

65
use std::mem;
@@ -9,15 +8,15 @@ use std::cell::UnsafeCell;
98
const WRITE_AFTER_CAST: () = unsafe {
109
let mut x = 0;
1110
let ptr = &x as *const i32 as *mut i32;
12-
*ptr = 0; //~ERROR: writes_through_immutable_pointer
13-
//~^ previously accepted
11+
*ptr = 0; //~ERROR: evaluation of constant value failed
12+
//~| immutable
1413
};
1514

1615
const WRITE_AFTER_TRANSMUTE: () = unsafe {
1716
let mut x = 0;
1817
let ptr: *mut i32 = mem::transmute(&x);
19-
*ptr = 0; //~ERROR: writes_through_immutable_pointer
20-
//~^ previously accepted
18+
*ptr = 0; //~ERROR: evaluation of constant value failed
19+
//~| immutable
2120
};
2221

2322
// it's okay when there is interior mutability;

‎tests/ui/consts/const-eval/ub-write-through-immutable.stderr

+7-47
Original file line numberDiff line numberDiff line change
@@ -1,55 +1,15 @@
1-
error: writing through a pointer that was derived from a shared (immutable) reference
2-
--> $DIR/ub-write-through-immutable.rs:12:5
1+
error[E0080]: evaluation of constant value failed
2+
--> $DIR/ub-write-through-immutable.rs:11:5
33
|
44
LL | *ptr = 0;
5-
| ^^^^^^^^
6-
|
7-
= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
8-
= note: for more information, see issue #X <https://github.com/rust-lang/rust/issues/X>
9-
note: the lint level is defined here
10-
--> $DIR/ub-write-through-immutable.rs:3:9
11-
|
12-
LL | #![deny(writes_through_immutable_pointer)]
13-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
5+
| ^^^^^^^^ writing through a pointer that was derived from a shared (immutable) reference
146

15-
error: writing through a pointer that was derived from a shared (immutable) reference
16-
--> $DIR/ub-write-through-immutable.rs:19:5
7+
error[E0080]: evaluation of constant value failed
8+
--> $DIR/ub-write-through-immutable.rs:18:5
179
|
1810
LL | *ptr = 0;
19-
| ^^^^^^^^
20-
|
21-
= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
22-
= note: for more information, see issue #X <https://github.com/rust-lang/rust/issues/X>
11+
| ^^^^^^^^ writing through a pointer that was derived from a shared (immutable) reference
2312

2413
error: aborting due to 2 previous errors
2514

26-
Future incompatibility report: Future breakage diagnostic:
27-
error: writing through a pointer that was derived from a shared (immutable) reference
28-
--> $DIR/ub-write-through-immutable.rs:12:5
29-
|
30-
LL | *ptr = 0;
31-
| ^^^^^^^^
32-
|
33-
= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
34-
= note: for more information, see issue #X <https://github.com/rust-lang/rust/issues/X>
35-
note: the lint level is defined here
36-
--> $DIR/ub-write-through-immutable.rs:3:9
37-
|
38-
LL | #![deny(writes_through_immutable_pointer)]
39-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
40-
41-
Future breakage diagnostic:
42-
error: writing through a pointer that was derived from a shared (immutable) reference
43-
--> $DIR/ub-write-through-immutable.rs:19:5
44-
|
45-
LL | *ptr = 0;
46-
| ^^^^^^^^
47-
|
48-
= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
49-
= note: for more information, see issue #X <https://github.com/rust-lang/rust/issues/X>
50-
note: the lint level is defined here
51-
--> $DIR/ub-write-through-immutable.rs:3:9
52-
|
53-
LL | #![deny(writes_through_immutable_pointer)]
54-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
55-
15+
For more information about this error, try `rustc --explain E0080`.

0 commit comments

Comments
 (0)