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RalfJungfmease
RalfJung
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fmease
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repr(transparent): it's fine if the one non-1-ZST field is a ZST
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-87
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4 files changed

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‎compiler/rustc_hir_analysis/messages.ftl

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -276,13 +276,13 @@ hir_analysis_transparent_enum_variant = transparent enum needs exactly one varia
276276
.many_label = too many variants in `{$path}`
277277
.multi_label = variant here
278278
279-
hir_analysis_transparent_non_zero_sized = transparent {$desc} needs at most one non-zero-sized field, but has {$field_count}
280-
.label = needs at most one non-zero-sized field, but has {$field_count}
281-
.labels = this field is non-zero-sized
279+
hir_analysis_transparent_non_zero_sized = transparent {$desc} needs at most one field with non-trivial size or alignment, but has {$field_count}
280+
.label = needs at most one field with non-trivial size or alignment, but has {$field_count}
281+
.labels = this field has non-zero size or requires alignment
282282
283-
hir_analysis_transparent_non_zero_sized_enum = the variant of a transparent {$desc} needs at most one non-zero-sized field, but has {$field_count}
284-
.label = needs at most one non-zero-sized field, but has {$field_count}
285-
.labels = this field is non-zero-sized
283+
hir_analysis_transparent_non_zero_sized_enum = the variant of a transparent {$desc} needs at most one field with non-trivial size or alignment, but has {$field_count}
284+
.label = needs at most one field with non-trivial size or alignment, but has {$field_count}
285+
.labels = this field has non-zero size or requires alignment
286286
287287
hir_analysis_typeof_reserved_keyword_used =
288288
`typeof` is a reserved keyword but unimplemented

‎compiler/rustc_hir_analysis/src/check/check.rs

Lines changed: 21 additions & 37 deletions
Original file line numberDiff line numberDiff line change
@@ -1130,19 +1130,19 @@ pub(super) fn check_transparent<'tcx>(tcx: TyCtxt<'tcx>, adt: ty::AdtDef<'tcx>)
11301130
return;
11311131
}
11321132

1133-
// For each field, figure out if it's known to be a ZST and align(1), with "known"
1134-
// respecting #[non_exhaustive] attributes.
1133+
// For each field, figure out if it's known to have "trivial" layout (i.e., is a 1-ZST), with
1134+
// "known" respecting #[non_exhaustive] attributes.
11351135
let field_infos = adt.all_fields().map(|field| {
11361136
let ty = field.ty(tcx, GenericArgs::identity_for_item(tcx, field.did));
11371137
let param_env = tcx.param_env(field.did);
11381138
let layout = tcx.layout_of(param_env.and(ty));
11391139
// We are currently checking the type this field came from, so it must be local
11401140
let span = tcx.hir().span_if_local(field.did).unwrap();
1141-
let zst = layout.is_ok_and(|layout| layout.is_zst());
1142-
let align = layout.ok().map(|layout| layout.align.abi.bytes());
1143-
if !zst {
1144-
return (span, zst, align, None);
1141+
let trivial = layout.is_ok_and(|layout| layout.is_1zst());
1142+
if !trivial {
1143+
return (span, trivial, None);
11451144
}
1145+
// Even some 1-ZST fields are not allowed though, if they have `non_exhaustive`.
11461146

11471147
fn check_non_exhaustive<'tcx>(
11481148
tcx: TyCtxt<'tcx>,
@@ -1176,41 +1176,25 @@ pub(super) fn check_transparent<'tcx>(tcx: TyCtxt<'tcx>, adt: ty::AdtDef<'tcx>)
11761176
}
11771177
}
11781178

1179-
(span, zst, align, check_non_exhaustive(tcx, ty).break_value())
1179+
(span, trivial, check_non_exhaustive(tcx, ty).break_value())
11801180
});
11811181

1182-
let non_zst_fields = field_infos
1182+
let non_trivial_fields = field_infos
11831183
.clone()
1184-
.filter_map(|(span, zst, _align, _non_exhaustive)| if !zst { Some(span) } else { None });
1185-
let non_zst_count = non_zst_fields.clone().count();
1186-
if non_zst_count >= 2 {
1187-
bad_non_zero_sized_fields(tcx, adt, non_zst_count, non_zst_fields, tcx.def_span(adt.did()));
1184+
.filter_map(|(span, trivial, _non_exhaustive)| if !trivial { Some(span) } else { None });
1185+
let non_trivial_count = non_trivial_fields.clone().count();
1186+
if non_trivial_count >= 2 {
1187+
bad_non_zero_sized_fields(
1188+
tcx,
1189+
adt,
1190+
non_trivial_count,
1191+
non_trivial_fields,
1192+
tcx.def_span(adt.did()),
1193+
);
1194+
return;
11881195
}
1189-
let incompatible_zst_fields =
1190-
field_infos.clone().filter(|(_, _, _, opt)| opt.is_some()).count();
1191-
let incompat = incompatible_zst_fields + non_zst_count >= 2 && non_zst_count < 2;
1192-
for (span, zst, align, non_exhaustive) in field_infos {
1193-
if zst && align != Some(1) {
1194-
let mut err = struct_span_err!(
1195-
tcx.sess,
1196-
span,
1197-
E0691,
1198-
"zero-sized field in transparent {} has alignment larger than 1",
1199-
adt.descr(),
1200-
);
1201-
1202-
if let Some(align_bytes) = align {
1203-
err.span_label(
1204-
span,
1205-
format!("has alignment of {align_bytes}, which is larger than 1"),
1206-
);
1207-
} else {
1208-
err.span_label(span, "may have alignment larger than 1");
1209-
}
1210-
1211-
err.emit();
1212-
}
1213-
if incompat && let Some((descr, def_id, args, non_exhaustive)) = non_exhaustive {
1196+
for (span, _trivial, non_exhaustive) in field_infos {
1197+
if let Some((descr, def_id, args, non_exhaustive)) = non_exhaustive {
12141198
tcx.struct_span_lint_hir(
12151199
REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS,
12161200
tcx.hir().local_def_id_to_hir_id(adt.did().expect_local()),

‎tests/ui/repr/repr-transparent.rs

Lines changed: 13 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -23,23 +23,26 @@ struct ContainsMultipleZst(PhantomData<*const i32>, NoFields);
2323
struct ContainsZstAndNonZst((), [i32; 2]);
2424

2525
#[repr(transparent)]
26-
struct MultipleNonZst(u8, u8); //~ ERROR needs at most one non-zero-sized field
26+
struct MultipleNonZst(u8, u8); //~ ERROR needs at most one field with non-trivial size or alignment
2727

2828
trait Mirror { type It: ?Sized; }
2929
impl<T: ?Sized> Mirror for T { type It = Self; }
3030

3131
#[repr(transparent)]
3232
pub struct StructWithProjection(f32, <f32 as Mirror>::It);
33-
//~^ ERROR needs at most one non-zero-sized field
33+
//~^ ERROR needs at most one field with non-trivial size or alignment
3434

3535
#[repr(transparent)]
36-
struct NontrivialAlignZst(u32, [u16; 0]); //~ ERROR alignment larger than 1
36+
struct NontrivialAlignZst(u32, [u16; 0]); //~ ERROR needs at most one field with non-trivial size or alignment
3737

3838
#[repr(align(32))]
3939
struct ZstAlign32<T>(PhantomData<T>);
4040

4141
#[repr(transparent)]
42-
struct GenericAlign<T>(ZstAlign32<T>, u32); //~ ERROR alignment larger than 1
42+
struct GenericAlign<T>(ZstAlign32<T>, u32); //~ ERROR needs at most one field with non-trivial size or alignment
43+
44+
#[repr(transparent)]
45+
struct WrapsZstWithAlignment([i32; 0]);
4346

4447
#[repr(transparent)] //~ ERROR unsupported representation for zero-variant enum
4548
enum Void {} //~ ERROR transparent enum needs exactly one variant, but has 0
@@ -58,7 +61,7 @@ enum UnitFieldEnum {
5861
enum TooManyFieldsEnum {
5962
Foo(u32, String),
6063
}
61-
//~^^^ ERROR transparent enum needs at most one non-zero-sized field, but has 2
64+
//~^^^ ERROR transparent enum needs at most one field with non-trivial size or alignment, but has 2
6265

6366
#[repr(transparent)]
6467
enum MultipleVariants { //~ ERROR transparent enum needs exactly one variant, but has 2
@@ -67,13 +70,13 @@ enum MultipleVariants { //~ ERROR transparent enum needs exactly one variant, bu
6770
}
6871

6972
#[repr(transparent)]
70-
enum NontrivialAlignZstEnum {
71-
Foo(u32, [u16; 0]), //~ ERROR alignment larger than 1
73+
enum NontrivialAlignZstEnum { //~ ERROR needs at most one field with non-trivial size or alignment
74+
Foo(u32, [u16; 0]),
7275
}
7376

7477
#[repr(transparent)]
75-
enum GenericAlignEnum<T> {
76-
Foo { bar: ZstAlign32<T>, baz: u32 } //~ ERROR alignment larger than 1
78+
enum GenericAlignEnum<T> { //~ ERROR needs at most one field with non-trivial size or alignment
79+
Foo { bar: ZstAlign32<T>, baz: u32 }
7780
}
7881

7982
#[repr(transparent)]
@@ -82,7 +85,7 @@ union UnitUnion {
8285
}
8386

8487
#[repr(transparent)]
85-
union TooManyFields { //~ ERROR transparent union needs at most one non-zero-sized field, but has 2
88+
union TooManyFields { //~ ERROR transparent union needs at most one field with non-trivial size or alignment, but has 2
8689
u: u32,
8790
s: i32
8891
}

‎tests/ui/repr/repr-transparent.stderr

Lines changed: 48 additions & 34 deletions
Original file line numberDiff line numberDiff line change
@@ -1,59 +1,65 @@
1-
error[E0690]: transparent struct needs at most one non-zero-sized field, but has 2
1+
error[E0690]: transparent struct needs at most one field with non-trivial size or alignment, but has 2
22
--> $DIR/repr-transparent.rs:26:1
33
|
44
LL | struct MultipleNonZst(u8, u8);
5-
| ^^^^^^^^^^^^^^^^^^^^^ -- -- this field is non-zero-sized
5+
| ^^^^^^^^^^^^^^^^^^^^^ -- -- this field has non-zero size or requires alignment
66
| | |
7-
| | this field is non-zero-sized
8-
| needs at most one non-zero-sized field, but has 2
7+
| | this field has non-zero size or requires alignment
8+
| needs at most one field with non-trivial size or alignment, but has 2
99

10-
error[E0690]: transparent struct needs at most one non-zero-sized field, but has 2
10+
error[E0690]: transparent struct needs at most one field with non-trivial size or alignment, but has 2
1111
--> $DIR/repr-transparent.rs:32:1
1212
|
1313
LL | pub struct StructWithProjection(f32, <f32 as Mirror>::It);
14-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ --- ------------------- this field is non-zero-sized
14+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ --- ------------------- this field has non-zero size or requires alignment
1515
| | |
16-
| | this field is non-zero-sized
17-
| needs at most one non-zero-sized field, but has 2
16+
| | this field has non-zero size or requires alignment
17+
| needs at most one field with non-trivial size or alignment, but has 2
1818

19-
error[E0691]: zero-sized field in transparent struct has alignment larger than 1
20-
--> $DIR/repr-transparent.rs:36:32
19+
error[E0690]: transparent struct needs at most one field with non-trivial size or alignment, but has 2
20+
--> $DIR/repr-transparent.rs:36:1
2121
|
2222
LL | struct NontrivialAlignZst(u32, [u16; 0]);
23-
| ^^^^^^^^ has alignment of 2, which is larger than 1
23+
| ^^^^^^^^^^^^^^^^^^^^^^^^^ --- -------- this field has non-zero size or requires alignment
24+
| | |
25+
| | this field has non-zero size or requires alignment
26+
| needs at most one field with non-trivial size or alignment, but has 2
2427

25-
error[E0691]: zero-sized field in transparent struct has alignment larger than 1
26-
--> $DIR/repr-transparent.rs:42:24
28+
error[E0690]: transparent struct needs at most one field with non-trivial size or alignment, but has 2
29+
--> $DIR/repr-transparent.rs:42:1
2730
|
2831
LL | struct GenericAlign<T>(ZstAlign32<T>, u32);
29-
| ^^^^^^^^^^^^^ has alignment of 32, which is larger than 1
32+
| ^^^^^^^^^^^^^^^^^^^^^^ ------------- --- this field has non-zero size or requires alignment
33+
| | |
34+
| | this field has non-zero size or requires alignment
35+
| needs at most one field with non-trivial size or alignment, but has 2
3036

3137
error[E0084]: unsupported representation for zero-variant enum
32-
--> $DIR/repr-transparent.rs:44:1
38+
--> $DIR/repr-transparent.rs:47:1
3339
|
3440
LL | #[repr(transparent)]
3541
| ^^^^^^^^^^^^^^^^^^^^
3642
LL | enum Void {}
3743
| --------- zero-variant enum
3844

3945
error[E0731]: transparent enum needs exactly one variant, but has 0
40-
--> $DIR/repr-transparent.rs:45:1
46+
--> $DIR/repr-transparent.rs:48:1
4147
|
4248
LL | enum Void {}
4349
| ^^^^^^^^^ needs exactly one variant, but has 0
4450

45-
error[E0690]: the variant of a transparent enum needs at most one non-zero-sized field, but has 2
46-
--> $DIR/repr-transparent.rs:58:1
51+
error[E0690]: the variant of a transparent enum needs at most one field with non-trivial size or alignment, but has 2
52+
--> $DIR/repr-transparent.rs:61:1
4753
|
4854
LL | enum TooManyFieldsEnum {
49-
| ^^^^^^^^^^^^^^^^^^^^^^ needs at most one non-zero-sized field, but has 2
55+
| ^^^^^^^^^^^^^^^^^^^^^^ needs at most one field with non-trivial size or alignment, but has 2
5056
LL | Foo(u32, String),
51-
| --- ------ this field is non-zero-sized
57+
| --- ------ this field has non-zero size or requires alignment
5258
| |
53-
| this field is non-zero-sized
59+
| this field has non-zero size or requires alignment
5460

5561
error[E0731]: transparent enum needs exactly one variant, but has 2
56-
--> $DIR/repr-transparent.rs:64:1
62+
--> $DIR/repr-transparent.rs:67:1
5763
|
5864
LL | enum MultipleVariants {
5965
| ^^^^^^^^^^^^^^^^^^^^^ needs exactly one variant, but has 2
@@ -62,29 +68,37 @@ LL | Foo(String),
6268
LL | Bar,
6369
| --- too many variants in `MultipleVariants`
6470

65-
error[E0691]: zero-sized field in transparent enum has alignment larger than 1
66-
--> $DIR/repr-transparent.rs:71:14
71+
error[E0690]: the variant of a transparent enum needs at most one field with non-trivial size or alignment, but has 2
72+
--> $DIR/repr-transparent.rs:73:1
6773
|
74+
LL | enum NontrivialAlignZstEnum {
75+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ needs at most one field with non-trivial size or alignment, but has 2
6876
LL | Foo(u32, [u16; 0]),
69-
| ^^^^^^^^ has alignment of 2, which is larger than 1
77+
| --- -------- this field has non-zero size or requires alignment
78+
| |
79+
| this field has non-zero size or requires alignment
7080

71-
error[E0691]: zero-sized field in transparent enum has alignment larger than 1
72-
--> $DIR/repr-transparent.rs:76:11
81+
error[E0690]: the variant of a transparent enum needs at most one field with non-trivial size or alignment, but has 2
82+
--> $DIR/repr-transparent.rs:78:1
7383
|
84+
LL | enum GenericAlignEnum<T> {
85+
| ^^^^^^^^^^^^^^^^^^^^^^^^ needs at most one field with non-trivial size or alignment, but has 2
7486
LL | Foo { bar: ZstAlign32<T>, baz: u32 }
75-
| ^^^^^^^^^^^^^^^^^^ has alignment of 32, which is larger than 1
87+
| ------------------ -------- this field has non-zero size or requires alignment
88+
| |
89+
| this field has non-zero size or requires alignment
7690

77-
error[E0690]: transparent union needs at most one non-zero-sized field, but has 2
78-
--> $DIR/repr-transparent.rs:85:1
91+
error[E0690]: transparent union needs at most one field with non-trivial size or alignment, but has 2
92+
--> $DIR/repr-transparent.rs:88:1
7993
|
8094
LL | union TooManyFields {
81-
| ^^^^^^^^^^^^^^^^^^^ needs at most one non-zero-sized field, but has 2
95+
| ^^^^^^^^^^^^^^^^^^^ needs at most one field with non-trivial size or alignment, but has 2
8296
LL | u: u32,
83-
| ------ this field is non-zero-sized
97+
| ------ this field has non-zero size or requires alignment
8498
LL | s: i32
85-
| ------ this field is non-zero-sized
99+
| ------ this field has non-zero size or requires alignment
86100

87101
error: aborting due to 11 previous errors
88102

89-
Some errors have detailed explanations: E0084, E0690, E0691, E0731.
103+
Some errors have detailed explanations: E0084, E0690, E0731.
90104
For more information about an error, try `rustc --explain E0084`.

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