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Reject extra fields in MGCA struct const arguments #157886

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Reject extra fields in MGCA struct const arguments #157886

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8da99a0
add test to show extra field in mgca adt const arg
Shourya742 Jun 14, 2026
86efd4b
make sure check if there are extra fields or not.
Shourya742 Jun 14, 2026
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10 changes: 10 additions & 0 deletions compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2591,6 +2591,16 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
let variant_def = adt_def.variant_with_id(variant_did);
let variant_idx = adt_def.variant_index_with_id(variant_did).as_u32();

for init in inits {
if !variant_def.fields.iter().any(|field_def| field_def.name == init.field.name) {
let err = tcx.dcx().struct_span_err(
init.field.span,
format!("struct expression has no field named `{}`", init.field),
);
return ty::Const::new_error(tcx, err.emit());
}
}

Comment on lines +2594 to +2603

@Shourya742 Shourya742 Jun 14, 2026 •
edited by rustbot
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Currently, lower_const_arg_struct handled missing and duplicate initializers, but it did not check for extra fields. This checkd for fields that do not exist on the target variant.

View changes since the review

let fields = variant_def
.fields
.iter()
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11 changes: 11 additions & 0 deletions tests/ui/const-generics/mgca/adt_expr_unit_struct_extra_field.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,11 @@
#![feature(min_generic_const_args, adt_const_params)]

#[derive(Eq, PartialEq, std::marker::ConstParamTy)]
struct Foo;

fn foo<const N: Foo>() {}

fn main() {
foo::<{ Foo { field: const { 1 } } }>();
//~^ ERROR struct expression has no field named `field`
}
8 changes: 8 additions & 0 deletions tests/ui/const-generics/mgca/adt_expr_unit_struct_extra_field.stderr
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@@ -0,0 +1,8 @@
error: struct expression has no field named `field`
--> $DIR/adt_expr_unit_struct_extra_field.rs:9:19
|
LL | foo::<{ Foo { field: const { 1 } } }>();
| ^^^^^

error: aborting due to 1 previous error

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