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Improve diagnostic for E0691 #98071

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09c6c54
Improve diagnostic for E0691
Jun 13, 2022
bd3d1ae
fix error (maybe), use short/inline suggestions
Jun 13, 2022
5c2d5dc
print alignment in error message, if it is known
Jun 13, 2022
ebd42e5
Split `zero_sized_array` from `zst`
Jun 14, 2022
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73 changes: 50 additions & 23 deletions compiler/rustc_typeck/src/check/check.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,9 @@ use rustc_middle::hir::nested_filter;
use rustc_middle::ty::layout::{LayoutError, MAX_SIMD_LANES};
use rustc_middle::ty::subst::GenericArgKind;
use rustc_middle::ty::util::{Discr, IntTypeExt};
use rustc_middle::ty::{self, ParamEnv, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable};
use rustc_middle::ty::{
self, Array, ParamEnv, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable,
};
use rustc_session::lint::builtin::{UNINHABITED_STATIC, UNSUPPORTED_CALLING_CONVENTIONS};
use rustc_span::symbol::sym;
use rustc_span::{self, Span};
Expand Down Expand Up @@ -1204,17 +1206,17 @@ pub(super) fn check_packed(tcx: TyCtxt<'_>, sp: Span, def: ty::AdtDef<'_>) {
for attr in tcx.get_attrs(def.did(), sym::repr) {
for r in attr::parse_repr_attr(&tcx.sess, attr) {
if let attr::ReprPacked(pack) = r
&& let Some(repr_pack) = repr.pack
&& pack as u64 != repr_pack.bytes()
{
struct_span_err!(
tcx.sess,
sp,
E0634,
"type has conflicting packed representation hints"
)
.emit();
}
&& let Some(repr_pack) = repr.pack
&& pack as u64 != repr_pack.bytes()
{
struct_span_err!(
tcx.sess,
sp,
E0634,
"type has conflicting packed representation hints"
)
.emit();
}
}
}
if repr.align.is_some() {
Expand Down Expand Up @@ -1327,28 +1329,53 @@ pub(super) fn check_transparent<'tcx>(tcx: TyCtxt<'tcx>, sp: Span, adt: ty::AdtD
let layout = tcx.layout_of(param_env.and(ty));
// We are currently checking the type this field came from, so it must be local
let span = tcx.hir().span_if_local(field.did).unwrap();
let zst = layout.map_or(false, |layout| layout.is_zst());
let align1 = layout.map_or(false, |layout| layout.align.abi.bytes() == 1);
(span, zst, align1)
let array_len = match ty.kind() {
Array(_, len) => len.try_eval_usize(tcx, param_env),
_ => None,
};
let zst = array_len == Some(0) || layout.map_or(false, |layout| layout.is_zst());
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Wait, doesn't this change the actual typechecking behavior?

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well, i guess not necessarily, because the align check below will still fail?

I would rather move this is-array check to line 1348, like if (zst || zero_sized_array) && align != Some(1) so we don't need to edit this logic, just in case?

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I've split zero_sized_array from zst, but the logic stays the same, otherwise we would get #98064 again.

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Also with a more complex zero-sized but non-trivially-aligned field, we still get the same wrong diagnostic:

struct ComplexZst<A, B> {
    a: [A; 0],
    b: [B; 0],
}

#[repr(transparent)]
struct Aligned<T, A, B> {
    align: ComplexZst<A, B>,
    value: T,
}
error[E0690]: transparent struct needs at most one non-zero-sized field, but has 2
 --> src/lib.rs:7:1
  |
7 | struct Aligned<T, A, B> {
  | ^^^^^^^^^^^^^^^^^^^^^^^ needs at most one non-zero-sized field, but has 2
8 |     align: ComplexZst<A, B>,
  |     ----------------------- this field is non-zero-sized
9 |     value: T,
  |     -------- this field is non-zero-sized

For more information about this error, try `rustc --explain E0690`.

Is it worth trying to fix this? Should there be something like ty.is_zst(tcx, param_env)? I am not really experienced with rustc internals.

let align = layout.ok().map(|layout| layout.align.abi.bytes());
(span, zst, align)
});

let non_zst_fields =
field_infos.clone().filter_map(|(span, zst, _align1)| if !zst { Some(span) } else { None });
field_infos.clone().filter_map(|(span, zst, _align)| if !zst { Some(span) } else { None });
let non_zst_count = non_zst_fields.clone().count();
if non_zst_count >= 2 {
bad_non_zero_sized_fields(tcx, adt, non_zst_count, non_zst_fields, sp);
}
for (span, zst, align1) in field_infos {
if zst && !align1 {
struct_span_err!(
for (span, zst, align) in field_infos {
if zst && align != Some(1) {
let mut err = struct_span_err!(
tcx.sess,
span,
E0691,
"zero-sized field in transparent {} has alignment larger than 1",
adt.descr(),
)
.span_label(span, "has alignment larger than 1")
.emit();
);

if align.is_none() {
err.span_label(span, "may have alignment larger than 1");
} else {
err.span_label(span, "has alignment larger than 1");
};

if let Some(item_list) =
tcx.get_attr(adt.did(), sym::repr).and_then(|attr| attr.meta_item_list())
{
for item in item_list {
if item.name_or_empty() == sym::transparent {
err.span_suggestion_short(
item.span(),
"Try using `repr(C)` instead",
"C",
Applicability::MachineApplicable,
);
}
}
}

err.emit();
}
}
}
Expand Down Expand Up @@ -1475,7 +1502,7 @@ fn format_discriminant_overflow<'tcx>(
&& let rustc_ast::LitKind::Int(lit_value, _int_kind) = &lit.node
&& dis.val != *lit_value
{
return format!("`{dis}` (overflowed from `{lit_value}`)");
return format!("`{dis}` (overflowed from `{lit_value}`)");
}
}

Expand Down
8 changes: 8 additions & 0 deletions src/test/ui/repr/repr-transparent.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,9 @@ struct ZstAlign32<T>(PhantomData<T>);
#[repr(transparent)]
struct GenericAlign<T>(ZstAlign32<T>, u32); //~ ERROR alignment larger than 1

#[repr(transparent)]
struct GenericAlignZeroArray<T>([T; 0], u32); //~ ERROR alignment larger than 1

#[repr(transparent)] //~ ERROR unsupported representation for zero-variant enum
enum Void {} //~ ERROR transparent enum needs exactly one variant, but has 0

Expand Down Expand Up @@ -76,6 +79,11 @@ enum GenericAlignEnum<T> {
Foo { bar: ZstAlign32<T>, baz: u32 } //~ ERROR alignment larger than 1
}

#[repr(transparent)]
enum GenericAlignEnumZeroArray<T> {
Foo { bar: [T; 0], baz: u32 } //~ ERROR alignment larger than 1
}

#[repr(transparent)]
union UnitUnion {
u: (),
Expand Down
43 changes: 35 additions & 8 deletions src/test/ui/repr/repr-transparent.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -21,31 +21,43 @@ LL | pub struct StructWithProjection(f32, <f32 as Mirror>::It);
error[E0691]: zero-sized field in transparent struct has alignment larger than 1
--> $DIR/repr-transparent.rs:36:32
|
LL | #[repr(transparent)]
| ----------- help: Try using `repr(C)` instead
LL | struct NontrivialAlignZst(u32, [u16; 0]);
| ^^^^^^^^ has alignment larger than 1

error[E0691]: zero-sized field in transparent struct has alignment larger than 1
--> $DIR/repr-transparent.rs:42:24
|
LL | #[repr(transparent)]
| ----------- help: Try using `repr(C)` instead
LL | struct GenericAlign<T>(ZstAlign32<T>, u32);
| ^^^^^^^^^^^^^ has alignment larger than 1

error[E0691]: zero-sized field in transparent struct has alignment larger than 1
--> $DIR/repr-transparent.rs:45:33
|
LL | #[repr(transparent)]
| ----------- help: Try using `repr(C)` instead
LL | struct GenericAlignZeroArray<T>([T; 0], u32);
| ^^^^^^ may have alignment larger than 1

error[E0084]: unsupported representation for zero-variant enum
--> $DIR/repr-transparent.rs:44:1
--> $DIR/repr-transparent.rs:47:1
|
LL | #[repr(transparent)]
| ^^^^^^^^^^^^^^^^^^^^
LL | enum Void {}
| ------------ zero-variant enum

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

error[E0690]: the variant of a transparent enum needs at most one non-zero-sized field, but has 2
--> $DIR/repr-transparent.rs:58:1
--> $DIR/repr-transparent.rs:61:1
|
LL | enum TooManyFieldsEnum {
| ^^^^^^^^^^^^^^^^^^^^^^ needs at most one non-zero-sized field, but has 2
Expand All @@ -55,7 +67,7 @@ LL | Foo(u32, String),
| this field is non-zero-sized

error[E0731]: transparent enum needs exactly one variant, but has 2
--> $DIR/repr-transparent.rs:64:1
--> $DIR/repr-transparent.rs:67:1
|
LL | enum MultipleVariants {
| ^^^^^^^^^^^^^^^^^^^^^ needs exactly one variant, but has 2
Expand All @@ -65,19 +77,34 @@ LL | Bar,
| --- too many variants in `MultipleVariants`

error[E0691]: zero-sized field in transparent enum has alignment larger than 1
--> $DIR/repr-transparent.rs:71:14
--> $DIR/repr-transparent.rs:74:14
|
LL | #[repr(transparent)]
| ----------- help: Try using `repr(C)` instead
LL | enum NontrivialAlignZstEnum {
LL | Foo(u32, [u16; 0]),
| ^^^^^^^^ has alignment larger than 1

error[E0691]: zero-sized field in transparent enum has alignment larger than 1
--> $DIR/repr-transparent.rs:76:11
--> $DIR/repr-transparent.rs:79:11
|
LL | #[repr(transparent)]
| ----------- help: Try using `repr(C)` instead
LL | enum GenericAlignEnum<T> {
LL | Foo { bar: ZstAlign32<T>, baz: u32 }
| ^^^^^^^^^^^^^^^^^^ has alignment larger than 1

error[E0691]: zero-sized field in transparent enum has alignment larger than 1
--> $DIR/repr-transparent.rs:84:11
|
LL | #[repr(transparent)]
| ----------- help: Try using `repr(C)` instead
LL | enum GenericAlignEnumZeroArray<T> {
LL | Foo { bar: [T; 0], baz: u32 }
| ^^^^^^^^^^^ may have alignment larger than 1

error[E0690]: transparent union needs at most one non-zero-sized field, but has 2
--> $DIR/repr-transparent.rs:85:1
--> $DIR/repr-transparent.rs:93:1
|
LL | union TooManyFields {
| ^^^^^^^^^^^^^^^^^^^ needs at most one non-zero-sized field, but has 2
Expand All @@ -86,7 +113,7 @@ LL | u: u32,
LL | s: i32
| ------ this field is non-zero-sized

error: aborting due to 11 previous errors
error: aborting due to 13 previous errors

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