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Make #[repr(Rust)] incompatible with other (non-modifier) representation hints like C and simd #116829

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merged 1 commit into from
Oct 19, 2023
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Make #[repr(Rust)] incompatible with other (non-modifier) representation hints like C and simd #116829

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13 changes: 10 additions & 3 deletions compiler/rustc_passes/src/check_attr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1767,6 +1767,7 @@ impl CheckAttrVisitor<'_> {
.collect();

let mut int_reprs = 0;
let mut is_explicit_rust = false;
let mut is_c = false;
let mut is_simd = false;
let mut is_transparent = false;
Expand All @@ -1778,7 +1779,9 @@ impl CheckAttrVisitor<'_> {
}

match hint.name_or_empty() {
sym::Rust => {}
sym::Rust => {
is_explicit_rust = true;
}
sym::C => {
is_c = true;
match target {
Expand Down Expand Up @@ -1888,12 +1891,16 @@ impl CheckAttrVisitor<'_> {

// Error on repr(transparent, <anything else>).
if is_transparent && hints.len() > 1 {
let hint_spans: Vec<_> = hint_spans.clone().collect();
let hint_spans = hint_spans.clone().collect();
self.tcx.sess.emit_err(errors::TransparentIncompatible {
hint_spans,
target: target.to_string(),
});
}
if is_explicit_rust && (int_reprs > 0 || is_c || is_simd) {
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I could also turn the bools into a bitfield and check if the difference between the set bitflags and {Rust, align, packed} is empty to address “but not necessarily limited to” part of

We should ban all other repr(Rust, other) combinations, including, but not necesseraly limited to

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I think refactoring this function would be a lot of good, as the current code seems to be error-prone and confusing. But obv this refactoring can come as a follow-up, which does not need a backport. (cc me if you'll do it please)

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One of the things that would be nice is to default to disallowing, so that no changes can accidentally allow new combinations.

let hint_spans = hint_spans.clone().collect();
self.tcx.sess.emit_err(errors::ReprConflicting { hint_spans });
}
// Warn on repr(u8, u16), repr(C, simd), and c-like-enum-repr(C, u8)
if (int_reprs > 1)
|| (is_simd && is_c)
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Expand All @@ -1910,7 +1917,7 @@ impl CheckAttrVisitor<'_> {
CONFLICTING_REPR_HINTS,
hir_id,
hint_spans.collect::<Vec<Span>>(),
errors::ReprConflicting,
errors::ReprConflictingLint,
);
}
}
Expand Down
9 changes: 8 additions & 1 deletion compiler/rustc_passes/src/errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -558,9 +558,16 @@ pub struct ReprIdent {
pub span: Span,
}

#[derive(Diagnostic)]
#[diag(passes_repr_conflicting, code = "E0566")]
pub struct ReprConflicting {
#[primary_span]
pub hint_spans: Vec<Span>,
}

#[derive(LintDiagnostic)]
#[diag(passes_repr_conflicting, code = "E0566")]
pub struct ReprConflicting;
pub struct ReprConflictingLint;
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If you're interested in a follow-up, it's probably time to bump this lint up to a hard-error 😸


#[derive(Diagnostic)]
#[diag(passes_used_static)]
Expand Down
23 changes: 23 additions & 0 deletions tests/ui/repr/explicit-rust-repr-conflicts.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,23 @@
#[repr(C, Rust)] //~ ERROR conflicting representation hints
struct S {
a: i32,
}


#[repr(Rust)] //~ ERROR conflicting representation hints
#[repr(C)]
struct T {
a: i32,
}

#[repr(Rust, u64)] //~ ERROR conflicting representation hints
enum U {
V,
}

#[repr(Rust, simd)]
//~^ ERROR conflicting representation hints
//~| ERROR SIMD types are experimental and possibly buggy
struct F32x4(f32, f32, f32, f32);

fn main() {}
39 changes: 39 additions & 0 deletions tests/ui/repr/explicit-rust-repr-conflicts.stderr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,39 @@
error[E0658]: SIMD types are experimental and possibly buggy
--> $DIR/explicit-rust-repr-conflicts.rs:18:1
|
LL | #[repr(Rust, simd)]
| ^^^^^^^^^^^^^^^^^^^
|
= note: see issue #27731 <https://github.com/rust-lang/rust/issues/27731> for more information
= help: add `#![feature(repr_simd)]` to the crate attributes to enable

error[E0566]: conflicting representation hints
--> $DIR/explicit-rust-repr-conflicts.rs:1:8
|
LL | #[repr(C, Rust)]
| ^ ^^^^

error[E0566]: conflicting representation hints
--> $DIR/explicit-rust-repr-conflicts.rs:7:8
|
LL | #[repr(Rust)]
| ^^^^
LL | #[repr(C)]
| ^

error[E0566]: conflicting representation hints
--> $DIR/explicit-rust-repr-conflicts.rs:13:8
|
LL | #[repr(Rust, u64)]
| ^^^^ ^^^

error[E0566]: conflicting representation hints
--> $DIR/explicit-rust-repr-conflicts.rs:18:8
|
LL | #[repr(Rust, simd)]
| ^^^^ ^^^^

error: aborting due to 5 previous errors

Some errors have detailed explanations: E0566, E0658.
For more information about an error, try `rustc --explain E0566`.
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