diff --git a/compiler/rustc_ast_lowering/messages.ftl b/compiler/rustc_ast_lowering/messages.ftl
index 5ef76fb64aaf2..50eb7c7ae99bd 100644
--- a/compiler/rustc_ast_lowering/messages.ftl
+++ b/compiler/rustc_ast_lowering/messages.ftl
@@ -179,6 +179,8 @@ ast_lowering_underscore_expr_lhs_assign =
in expressions, `_` can only be used on the left-hand side of an assignment
.label = `_` not allowed here
+ast_lowering_union_default_field_values = unions cannot have default field values
+
ast_lowering_unstable_inline_assembly = inline assembly is not stable yet on this architecture
ast_lowering_unstable_inline_assembly_label_operand_with_outputs =
using both label and output operands for inline assembly is unstable
diff --git a/compiler/rustc_ast_lowering/src/errors.rs b/compiler/rustc_ast_lowering/src/errors.rs
index 576fa9731e906..b444324ef9143 100644
--- a/compiler/rustc_ast_lowering/src/errors.rs
+++ b/compiler/rustc_ast_lowering/src/errors.rs
@@ -475,3 +475,10 @@ pub(crate) struct UseConstGenericArg {
#[suggestion_part(code = "{other_args}")]
pub call_args: Span,
}
+
+#[derive(Diagnostic)]
+#[diag(ast_lowering_union_default_field_values)]
+pub(crate) struct UnionWithDefault {
+ #[primary_span]
+ pub span: Span,
+}
diff --git a/compiler/rustc_ast_lowering/src/item.rs b/compiler/rustc_ast_lowering/src/item.rs
index 49110c93954ad..ef27d0ef69b14 100644
--- a/compiler/rustc_ast_lowering/src/item.rs
+++ b/compiler/rustc_ast_lowering/src/item.rs
@@ -17,6 +17,7 @@ use tracing::instrument;
use super::errors::{
InvalidAbi, InvalidAbiSuggestion, MisplacedRelaxTraitBound, TupleStructWithDefault,
+ UnionWithDefault,
};
use super::stability::{enabled_names, gate_unstable_abi};
use super::{
@@ -316,7 +317,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
ImplTraitContext::Disallowed(ImplTraitPosition::Generic),
|this| {
this.arena.alloc_from_iter(
- enum_definition.variants.iter().map(|x| this.lower_variant(x)),
+ enum_definition.variants.iter().map(|x| this.lower_variant(i, x)),
)
},
);
@@ -328,7 +329,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
generics,
id,
ImplTraitContext::Disallowed(ImplTraitPosition::Generic),
- |this| this.lower_variant_data(hir_id, struct_def),
+ |this| this.lower_variant_data(hir_id, i, struct_def),
);
hir::ItemKind::Struct(ident, generics, struct_def)
}
@@ -338,7 +339,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
generics,
id,
ImplTraitContext::Disallowed(ImplTraitPosition::Generic),
- |this| this.lower_variant_data(hir_id, vdata),
+ |this| this.lower_variant_data(hir_id, i, vdata),
);
hir::ItemKind::Union(ident, generics, vdata)
}
@@ -714,13 +715,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
}
}
- fn lower_variant(&mut self, v: &Variant) -> hir::Variant<'hir> {
+ fn lower_variant(&mut self, item_kind: &ItemKind, v: &Variant) -> hir::Variant<'hir> {
let hir_id = self.lower_node_id(v.id);
self.lower_attrs(hir_id, &v.attrs, v.span);
hir::Variant {
hir_id,
def_id: self.local_def_id(v.id),
- data: self.lower_variant_data(hir_id, &v.data),
+ data: self.lower_variant_data(hir_id, item_kind, &v.data),
disr_expr: v.disr_expr.as_ref().map(|e| self.lower_anon_const_to_anon_const(e)),
ident: self.lower_ident(v.ident),
span: self.lower_span(v.span),
@@ -730,15 +731,36 @@ impl<'hir> LoweringContext<'_, 'hir> {
fn lower_variant_data(
&mut self,
parent_id: hir::HirId,
+ item_kind: &ItemKind,
vdata: &VariantData,
) -> hir::VariantData<'hir> {
match vdata {
- VariantData::Struct { fields, recovered } => hir::VariantData::Struct {
- fields: self
+ VariantData::Struct { fields, recovered } => {
+ let fields = self
.arena
- .alloc_from_iter(fields.iter().enumerate().map(|f| self.lower_field_def(f))),
- recovered: *recovered,
- },
+ .alloc_from_iter(fields.iter().enumerate().map(|f| self.lower_field_def(f)));
+
+ if let ItemKind::Union(..) = item_kind {
+ for field in &fields[..] {
+ if let Some(default) = field.default {
+ // Unions cannot derive `Default`, and it's not clear how to use default
+ // field values of unions if that was supported. Therefore, blanket reject
+ // trying to use field values with unions.
+ if self.tcx.features().default_field_values() {
+ self.dcx().emit_err(UnionWithDefault { span: default.span });
+ } else {
+ let _ = self.dcx().span_delayed_bug(
+ default.span,
+ "expected union default field values feature gate error but none \
+ was produced",
+ );
+ }
+ }
+ }
+ }
+
+ hir::VariantData::Struct { fields, recovered: *recovered }
+ }
VariantData::Tuple(fields, id) => {
let ctor_id = self.lower_node_id(*id);
self.alias_attrs(ctor_id, parent_id);
diff --git a/tests/ui/feature-gates/feature-gate-default-field-values.rs b/tests/ui/feature-gates/feature-gate-default-field-values.rs
index d2e41a7160259..4631f51b9d840 100644
--- a/tests/ui/feature-gates/feature-gate-default-field-values.rs
+++ b/tests/ui/feature-gates/feature-gate-default-field-values.rs
@@ -58,6 +58,16 @@ pub enum OptEnum {
}
}
+// Default field values may not be used on `union`s (at least, this is not described in the accepted
+// RFC, and it's not currently clear how to extend the design to do so). We emit a feature gate
+// error when the feature is not enabled, but syntactically reject default field values when used
+// with unions when the feature is enabled. This can be adjusted if there's an acceptable design
+// extension, or just unconditionally reject always.
+union U {
+ x: i32 = 0, //~ ERROR default values on fields are experimental
+ y: f32 = 0.0, //~ ERROR default values on fields are experimental
+}
+
fn main () {
let x = Foo { .. }; //~ ERROR base expression required after `..`
let y = Foo::default();
diff --git a/tests/ui/feature-gates/feature-gate-default-field-values.stderr b/tests/ui/feature-gates/feature-gate-default-field-values.stderr
index 104d72a39861d..292c38990726e 100644
--- a/tests/ui/feature-gates/feature-gate-default-field-values.stderr
+++ b/tests/ui/feature-gates/feature-gate-default-field-values.stderr
@@ -124,8 +124,28 @@ LL | optional: () = (),
= help: add `#![feature(default_field_values)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+error[E0658]: default values on fields are experimental
+ --> $DIR/feature-gate-default-field-values.rs:67:11
+ |
+LL | x: i32 = 0,
+ | ^^^^
+ |
+ = note: see issue #132162 <https://github.com/rust-lang/rust/issues/132162> for more information
+ = help: add `#![feature(default_field_values)]` to the crate attributes to enable
+ = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: default values on fields are experimental
+ --> $DIR/feature-gate-default-field-values.rs:68:11
+ |
+LL | y: f32 = 0.0,
+ | ^^^^^^
+ |
+ = note: see issue #132162 <https://github.com/rust-lang/rust/issues/132162> for more information
+ = help: add `#![feature(default_field_values)]` to the crate attributes to enable
+ = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:62:21
+ --> $DIR/feature-gate-default-field-values.rs:72:21
|
LL | let x = Foo { .. };
| ^
@@ -140,7 +160,7 @@ LL | let x = Foo { ../* expr */ };
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:64:29
+ --> $DIR/feature-gate-default-field-values.rs:74:29
|
LL | let z = Foo { baz: 1, .. };
| ^
@@ -155,7 +175,7 @@ LL | let z = Foo { baz: 1, ../* expr */ };
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:70:26
+ --> $DIR/feature-gate-default-field-values.rs:80:26
|
LL | let x = Bar::Foo { .. };
| ^
@@ -170,7 +190,7 @@ LL | let x = Bar::Foo { ../* expr */ };
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:72:34
+ --> $DIR/feature-gate-default-field-values.rs:82:34
|
LL | let z = Bar::Foo { baz: 1, .. };
| ^
@@ -185,7 +205,7 @@ LL | let z = Bar::Foo { baz: 1, ../* expr */ };
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:78:31
+ --> $DIR/feature-gate-default-field-values.rs:88:31
|
LL | let x = Qux::<i32, 4> { .. };
| ^
@@ -200,7 +220,7 @@ LL | let x = Qux::<i32, 4> { ../* expr */ };
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:79:73
+ --> $DIR/feature-gate-default-field-values.rs:89:73
|
LL | assert!(matches!(Qux::<i32, 4> { bar: S, baz: 42, bat: 2, bay: 4, .. }, x));
| ^
@@ -215,7 +235,7 @@ LL | assert!(matches!(Qux::<i32, 4> { bar: S, baz: 42, bat: 2, bay: 4, ../*
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:82:38
+ --> $DIR/feature-gate-default-field-values.rs:92:38
|
LL | let y = Opt { mandatory: None, .. };
| ^
@@ -230,7 +250,7 @@ LL | let y = Opt { mandatory: None, ../* expr */ };
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:86:47
+ --> $DIR/feature-gate-default-field-values.rs:96:47
|
LL | assert!(matches!(Opt { mandatory: None, .. }, z));
| ^
@@ -245,7 +265,7 @@ LL | assert!(matches!(Opt { mandatory: None, ../* expr */ }, z));
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:88:30
+ --> $DIR/feature-gate-default-field-values.rs:98:30
|
LL | assert!(matches!(Opt { .. }, z));
| ^
@@ -256,7 +276,7 @@ LL | assert!(matches!(Opt { ../* expr */ }, z));
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:90:44
+ --> $DIR/feature-gate-default-field-values.rs:100:44
|
LL | assert!(matches!(Opt { optional: (), .. }, z));
| ^
@@ -267,7 +287,7 @@ LL | assert!(matches!(Opt { optional: (), ../* expr */ }, z));
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:92:61
+ --> $DIR/feature-gate-default-field-values.rs:102:61
|
LL | assert!(matches!(Opt { optional: (), mandatory: None, .. }, z));
| ^
@@ -279,7 +299,7 @@ LL + assert!(matches!(Opt { optional: (), mandatory: None, }, z));
|
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:94:51
+ --> $DIR/feature-gate-default-field-values.rs:104:51
|
LL | let y = OptEnum::Variant { mandatory: None, .. };
| ^
@@ -294,7 +314,7 @@ LL | let y = OptEnum::Variant { mandatory: None, ../* expr */ };
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:98:60
+ --> $DIR/feature-gate-default-field-values.rs:108:60
|
LL | assert!(matches!(OptEnum::Variant { mandatory: None, .. }, z));
| ^
@@ -309,7 +329,7 @@ LL | assert!(matches!(OptEnum::Variant { mandatory: None, ../* expr */ }, z)
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:100:43
+ --> $DIR/feature-gate-default-field-values.rs:110:43
|
LL | assert!(matches!(OptEnum::Variant { .. }, z));
| ^
@@ -320,7 +340,7 @@ LL | assert!(matches!(OptEnum::Variant { ../* expr */ }, z));
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:102:57
+ --> $DIR/feature-gate-default-field-values.rs:112:57
|
LL | assert!(matches!(OptEnum::Variant { optional: (), .. }, z));
| ^
@@ -331,7 +351,7 @@ LL | assert!(matches!(OptEnum::Variant { optional: (), ../* expr */ }, z));
| ++++++++++
error[E0797]: base expression required after `..`
- --> $DIR/feature-gate-default-field-values.rs:104:74
+ --> $DIR/feature-gate-default-field-values.rs:114:74
|
LL | assert!(matches!(OptEnum::Variant { optional: (), mandatory: None, .. }, z));
| ^
@@ -342,7 +362,7 @@ LL - assert!(matches!(OptEnum::Variant { optional: (), mandatory: None, .. }
LL + assert!(matches!(OptEnum::Variant { optional: (), mandatory: None, }, z));
|
-error: aborting due to 29 previous errors
+error: aborting due to 31 previous errors
Some errors have detailed explanations: E0658, E0797.
For more information about an error, try `rustc --explain E0658`.
diff --git a/tests/ui/structs/default-field-values/failures.rs b/tests/ui/structs/default-field-values/failures.rs
index dee6566bd0ea1..9c5b7172929c6 100644
--- a/tests/ui/structs/default-field-values/failures.rs
+++ b/tests/ui/structs/default-field-values/failures.rs
@@ -49,6 +49,12 @@ enum E {
Variant {} //~ ERROR the `#[default]` attribute may only be used on unit enum variants
}
+union U
+{
+ x: i32 = 1, //~ ERROR unions cannot have default field values
+ y: f32 = 2., //~ ERROR unions cannot have default field values
+}
+
fn main () {
let _ = Foo { .. }; // ok
let _ = Foo::default(); // ok
diff --git a/tests/ui/structs/default-field-values/failures.stderr b/tests/ui/structs/default-field-values/failures.stderr
index aaa75fd3180c5..5e3d4c89c2a3c 100644
--- a/tests/ui/structs/default-field-values/failures.stderr
+++ b/tests/ui/structs/default-field-values/failures.stderr
@@ -12,6 +12,18 @@ error: default fields are not supported in tuple structs
LL | pub struct Rak(i32 = 42);
| ^^ default fields are only supported on structs
+error: unions cannot have default field values
+ --> $DIR/failures.rs:54:14
+ |
+LL | x: i32 = 1,
+ | ^
+
+error: unions cannot have default field values
+ --> $DIR/failures.rs:55:14
+ |
+LL | y: f32 = 2.,
+ | ^^
+
error[E0277]: the trait bound `S: Default` is not satisfied
--> $DIR/failures.rs:16:5
|
@@ -28,19 +40,19 @@ LL | pub struct S;
|
error: missing field `bar` in initializer
- --> $DIR/failures.rs:55:19
+ --> $DIR/failures.rs:61:19
|
LL | let _ = Bar { .. };
| ^ fields that do not have a defaulted value must be provided explicitly
error: missing field `bar` in initializer
- --> $DIR/failures.rs:56:27
+ --> $DIR/failures.rs:62:27
|
LL | let _ = Bar { baz: 0, .. };
| ^ fields that do not have a defaulted value must be provided explicitly
error[E0308]: mismatched types
- --> $DIR/failures.rs:60:17
+ --> $DIR/failures.rs:66:17
|
LL | let _ = Rak(..);
| --- ^^ expected `i32`, found `RangeFull`
@@ -53,19 +65,19 @@ note: tuple struct defined here
LL | pub struct Rak(i32 = 42);
| ^^^
help: you might have meant to use `..` to skip providing a value for expected fields, but this is only supported on non-tuple struct literals; it is instead interpreted as a `std::ops::RangeFull` literal
- --> $DIR/failures.rs:60:17
+ --> $DIR/failures.rs:66:17
|
LL | let _ = Rak(..);
| ^^
error[E0061]: this struct takes 1 argument but 2 arguments were supplied
- --> $DIR/failures.rs:62:13
+ --> $DIR/failures.rs:68:13
|
LL | let _ = Rak(0, ..);
| ^^^ -- unexpected argument #2 of type `RangeFull`
|
help: you might have meant to use `..` to skip providing a value for expected fields, but this is only supported on non-tuple struct literals; it is instead interpreted as a `std::ops::RangeFull` literal
- --> $DIR/failures.rs:62:20
+ --> $DIR/failures.rs:68:20
|
LL | let _ = Rak(0, ..);
| ^^
@@ -81,13 +93,13 @@ LL + let _ = Rak(0);
|
error[E0061]: this struct takes 1 argument but 2 arguments were supplied
- --> $DIR/failures.rs:64:13
+ --> $DIR/failures.rs:70:13
|
LL | let _ = Rak(.., 0);
| ^^^ -- unexpected argument #1 of type `RangeFull`
|
help: you might have meant to use `..` to skip providing a value for expected fields, but this is only supported on non-tuple struct literals; it is instead interpreted as a `std::ops::RangeFull` literal
- --> $DIR/failures.rs:64:17
+ --> $DIR/failures.rs:70:17
|
LL | let _ = Rak(.., 0);
| ^^
@@ -102,7 +114,7 @@ LL - let _ = Rak(.., 0);
LL + let _ = Rak(0);
|
-error: aborting due to 8 previous errors
+error: aborting due to 10 previous errors
Some errors have detailed explanations: E0061, E0277, E0308.
For more information about an error, try `rustc --explain E0061`.