Rollup merge of #157886 - Shourya742:2026-06-14-reject-extra-field-mgca-adt-const, r=camelid

Reject extra fields in MGCA struct const arguments

closes: #154538

r? @BoxyUwU

Author: JonathanBrouwer

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -2594,6 +2594,43 @@ 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 mut err = if adt_def.is_enum() {
+                    struct_span_code_err!(
+                        tcx.dcx(),
+                        init.field.span,
+                        E0559,
+                        "variant `{}::{}` has no field named `{}`",
+                        ty,
+                        variant_def.name,
+                        init.field
+                    )
+                } else {
+                    struct_span_code_err!(
+                        tcx.dcx(),
+                        init.field.span,
+                        E0560,
+                        "struct `{}` has no field named `{}`",
+                        variant_def.name,
+                        init.field
+                    )
+                };
+                if adt_def.is_enum() {
+                    err.span_label(
+                        init.field.span,
+                        format!("`{}::{}` does not have this field", ty, variant_def.name),
+                    );
+                } else {
+                    err.span_label(
+                        init.field.span,
+                        format!("`{}` does not have this field", variant_def.name),
+                    );
+                }
+                return ty::Const::new_error(tcx, err.emit());
+            }
+        }
+
         let fields = variant_def
             .fields
             .iter()

tests/ui/const-generics/mgca/adt_expr_unit_enum_extra_field.rs

@@ -0,0 +1,13 @@
+#![feature(min_generic_const_args, adt_const_params)]
+
+#[derive(Eq, PartialEq, std::marker::ConstParamTy)]
+enum E {
+    S {}
+}
+
+fn foo<const N: E>() {}
+
+fn main() {
+    foo::<{E::S { x: const { 1 } }}>();
+        //~^ ERROR variant `E::S` has no field named `x` [E0559]
+}

tests/ui/const-generics/mgca/adt_expr_unit_enum_extra_field.stderr

@@ -0,0 +1,9 @@
+error[E0559]: variant `E::S` has no field named `x`
+  --> $DIR/adt_expr_unit_enum_extra_field.rs:11:19
+   |
+LL |     foo::<{E::S { x: const { 1 } }}>();
+   |                   ^ `E::S` does not have this field
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0559`.

tests/ui/const-generics/mgca/adt_expr_unit_struct_extra_field.rs

@@ -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 `Foo` has no field named `field` [E0560]
+}

tests/ui/const-generics/mgca/adt_expr_unit_struct_extra_field.stderr

@@ -0,0 +1,9 @@
+error[E0560]: struct `Foo` has no field named `field`
+  --> $DIR/adt_expr_unit_struct_extra_field.rs:9:19
+   |
+LL |     foo::<{ Foo { field: const { 1 } } }>();
+   |                   ^^^^^ `Foo` does not have this field
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0560`.