remove custom impl error for field traits and use attribute instead

Author: BennoLossin

compiler/rustc_error_codes/src/error_codes/E0806.md

@@ -548,7 +548,6 @@ E0802: 0802,
 E0803: 0803,
 E0804: 0804,
 E0805: 0805,
-E0806: 0806,
         );
     )
 }

compiler/rustc_error_codes/src/lib.rs

@@ -161,9 +161,6 @@ hir_analysis_drop_impl_on_wrong_item =
     the `{$trait_}` trait may only be implemented for local structs, enums, and unions
     .label = must be a struct, enum, or union in the current crate
 
-hir_analysis_field_trait_impl =
-    the `{$trait_}` trait may not be implemented manually
-
 hir_analysis_drop_impl_reservation = reservation `Drop` impls are not supported
 
 hir_analysis_duplicate_precise_capture = cannot capture parameter `{$name}` twice

compiler/rustc_hir_analysis/messages.ftl

@@ -52,8 +52,6 @@ pub(super) fn check_trait<'tcx>(
         lang_items.coerce_pointee_validated_trait(),
         visit_implementation_of_coerce_pointee_validity,
     )?;
-    checker.check(lang_items.unaligned_field_trait(), visit_implementation_of_field_trait)?;
-    checker.check(lang_items.field_trait(), visit_implementation_of_field_trait)?;
     Ok(())
 }
 
@@ -376,18 +374,6 @@ fn visit_implementation_of_dispatch_from_dyn(checker: &Checker<'_>) -> Result<()
     }
 }
 
-fn visit_implementation_of_field_trait(checker: &Checker<'_>) -> Result<(), ErrorGuaranteed> {
-    let tcx = checker.tcx;
-    let impl_did = checker.impl_def_id;
-
-    let span = tcx.span_of_impl(impl_did.into()).expect("impl_did is local");
-
-    Err(tcx.dcx().emit_err(errors::FieldTraitImpl {
-        span,
-        trait_: tcx.item_name(checker.impl_header.trait_ref.skip_binder().def_id),
-    }))
-}
-
 pub(crate) fn coerce_unsized_info<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_did: LocalDefId,

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -208,14 +208,6 @@ pub(crate) struct DropImplOnWrongItem {
     pub trait_: Symbol,
 }
 
-#[derive(Diagnostic)]
-#[diag(hir_analysis_field_trait_impl, code = E0806)]
-pub(crate) struct FieldTraitImpl {
-    #[primary_span]
-    pub span: Span,
-    pub trait_: Symbol,
-}
-
 #[derive(Diagnostic)]
 pub(crate) enum FieldAlreadyDeclared {
     #[diag(hir_analysis_field_already_declared, code = E0124)]

compiler/rustc_hir_analysis/src/errors.rs

@@ -8,6 +8,8 @@
 /// byte offset `OFFSET`.
 #[lang = "UnalignedField"]
 #[unstable(feature = "field_projections", issue = "145383")]
+#[rustc_deny_explicit_impl]
+#[rustc_do_not_implement_via_object]
 pub unsafe trait UnalignedField: Sized {
     /// The type of the base where this field exists in.
     #[lang = "UnalignedFieldBase"]
@@ -30,6 +32,8 @@ pub unsafe trait UnalignedField: Sized {
 /// `Self::Type` is well-aligned.
 #[lang = "Field"]
 #[unstable(feature = "field_projections", issue = "145383")]
+#[rustc_deny_explicit_impl]
+#[rustc_do_not_implement_via_object]
 pub unsafe trait Field: UnalignedField {}
 
 /// Expands to the field representing type of the given field.

library/core/src/field.rs

@@ -7,12 +7,12 @@ use std::field::{Field, UnalignedField, field_of};
 pub struct MyStruct(usize);
 
 unsafe impl UnalignedField for MyStruct {
-    //~^ ERROR: the `UnalignedField` trait may not be implemented manually [E0806]
+    //~^ ERROR: explicit impls for the `UnalignedField` trait are not permitted [E0322]
     type Base = ();
     type Type = ();
     const OFFSET: usize = 0;
 }
 
-unsafe impl Field for field_of!(MyStruct, 0) {} //~ ERROR: the `Field` trait may not be implemented manually [E0806]
+unsafe impl Field for field_of!(MyStruct, 0) {} //~ ERROR: explicit impls for the `Field` trait are not permitted [E0322]
 
 fn main() {}

tests/ui/field_projections/deny-manual-impl.rs

@@ -1,15 +1,15 @@
-error[E0806]: the `UnalignedField` trait may not be implemented manually
+error[E0322]: explicit impls for the `UnalignedField` trait are not permitted
   --> $DIR/deny-manual-impl.rs:9:1
    |
 LL | unsafe impl UnalignedField for MyStruct {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl of `UnalignedField` not allowed
 
-error[E0806]: the `Field` trait may not be implemented manually
+error[E0322]: explicit impls for the `Field` trait are not permitted
   --> $DIR/deny-manual-impl.rs:16:1
    |
 LL | unsafe impl Field for field_of!(MyStruct, 0) {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl of `Field` not allowed
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0806`.
+For more information about this error, try `rustc --explain E0322`.