Add note when inherent impl for a alias type defined outside of the crate

compiler/rustc_hir_analysis/messages.ftl

@@ -241,7 +241,10 @@ hir_analysis_inherent_ty_outside = cannot define inherent `impl` for a type outs
 
 hir_analysis_inherent_ty_outside_new = cannot define inherent `impl` for a type outside of the crate where the type is defined
  .label = impl for type defined outside of crate
- .note = define and implement a trait or new type instead
+ .help = consider defining a trait and implementing it for the type or using a newtype wrapper like `struct MyType(ExternalType);` and implement it
+ .note = For more details about orphan rules, see <https://doc.rust-lang.org/reference/items/implementations.html?highlight=orphan#orphan-rules>
+
+hir_analysis_inherent_ty_outside_new_alias_note = `{$ty_name}` does not define a new type, just alias of `{$alias_ty_name}` defined here
 
 hir_analysis_inherent_ty_outside_primitive = cannot define inherent `impl` for primitive types outside of `core`
  .help = consider moving this inherent impl into `core` if possible

compiler/rustc_hir_analysis/src/coherence/inherent_impls.rs

@@ -107,7 +107,22 @@ impl<'tcx> InherentCollect<'tcx> {
  Ok(())
  } else {
  let impl_span = self.tcx.def_span(impl_def_id);
- Err(self.tcx.dcx().emit_err(errors::InherentTyOutsideNew { span: impl_span }))
+ let mut err = errors::InherentTyOutsideNew { span: impl_span, note: None };
+
+ if let hir::TyKind::Path(rustc_hir::QPath::Resolved(_, path)) =
+ self.tcx.hir_node_by_def_id(impl_def_id).expect_item().expect_impl().self_ty.kind
+ && let rustc_hir::def::Res::Def(DefKind::TyAlias, def_id) = path.res
+ {
+ let ty_name = self.tcx.def_path_str(def_id);
+ let alias_ty_name = self.tcx.type_of(def_id).skip_binder().to_string();
+ err.note = Some(errors::InherentTyOutsideNewAliasNote {
+ span: self.tcx.def_span(def_id),
+ ty_name,
+ alias_ty_name,
+ });
+ }
+
+ Err(self.tcx.dcx().emit_err(err))
  }
  }
 

compiler/rustc_hir_analysis/src/errors.rs

@@ -1178,11 +1178,23 @@ pub(crate) struct InherentTyOutsideRelevant {
 
 #[derive(Diagnostic)]
 #[diag(hir_analysis_inherent_ty_outside_new, code = E0116)]
+#[help]
 #[note]
 pub(crate) struct InherentTyOutsideNew {
  #[primary_span]
  #[label]
  pub span: Span,
+ #[subdiagnostic]
+ pub note: Option<InherentTyOutsideNewAliasNote>,
+}
+
+#[derive(Subdiagnostic)]
+#[note(hir_analysis_inherent_ty_outside_new_alias_note)]
+pub(crate) struct InherentTyOutsideNewAliasNote {
+ #[primary_span]
+ pub span: Span,
+ pub ty_name: String,
+ pub alias_ty_name: String,
 }
 
 #[derive(Diagnostic)]

tests/ui/error-codes/E0116.stderr

@@ -4,7 +4,8 @@ error[E0116]: cannot define inherent `impl` for a type outside of the crate wher
 LL | impl Vec<u8> {}
  | ^^^^^^^^^^^^ impl for type defined outside of crate
  |
- = note: define and implement a trait or new type instead
+ = help: consider defining a trait and implementing it for the type or using a newtype wrapper like `struct MyType(ExternalType);` and implement it
+ = note: For more details about orphan rules, see <https://doc.rust-lang.org/reference/items/implementations.html?highlight=orphan#orphan-rules>
 
 error: aborting due to 1 previous error
 

tests/ui/incoherent-inherent-impls/insufficient-suggestion-issue-141679.rs

@@ -0,0 +1,8 @@
+use std::rc::Rc;
+pub struct Foo;
+
+pub type Function = Rc<Foo>;
+
+impl Function {}
+//~^ ERROR cannot define inherent `impl` for a type outside of the crate where the type is defined [E0116]
+fn main(){}

tests/ui/incoherent-inherent-impls/insufficient-suggestion-issue-141679.stderr

@@ -0,0 +1,17 @@
+error[E0116]: cannot define inherent `impl` for a type outside of the crate where the type is defined
+ --> $DIR/insufficient-suggestion-issue-141679.rs:6:1
+ |
+LL | impl Function {}
+ | ^^^^^^^^^^^^^ impl for type defined outside of crate
+ |
+ = help: consider defining a trait and implementing it for the type or using a newtype wrapper like `struct MyType(ExternalType);` and implement it
+ = note: For more details about orphan rules, see <https://doc.rust-lang.org/reference/items/implementations.html?highlight=orphan#orphan-rules>
+note: `Function` does not define a new type, just alias of `Rc<Foo>` defined here
+ --> $DIR/insufficient-suggestion-issue-141679.rs:4:1
+ |
+LL | pub type Function = Rc<Foo>;
+ | ^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0116`.

tests/ui/incoherent-inherent-impls/no-attr-empty-impl.stderr

@@ -4,31 +4,35 @@ error[E0116]: cannot define inherent `impl` for a type outside of the crate wher
 LL | impl extern_crate::StructWithAttr {}
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl for type defined outside of crate
  |
- = note: define and implement a trait or new type instead
+ = help: consider defining a trait and implementing it for the type or using a newtype wrapper like `struct MyType(ExternalType);` and implement it
+ = note: For more details about orphan rules, see <https://doc.rust-lang.org/reference/items/implementations.html?highlight=orphan#orphan-rules>
 
 error[E0116]: cannot define inherent `impl` for a type outside of the crate where the type is defined
  --> $DIR/no-attr-empty-impl.rs:7:1
  |
 LL | impl extern_crate::StructNoAttr {}
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl for type defined outside of crate
  |
- = note: define and implement a trait or new type instead
+ = help: consider defining a trait and implementing it for the type or using a newtype wrapper like `struct MyType(ExternalType);` and implement it
+ = note: For more details about orphan rules, see <https://doc.rust-lang.org/reference/items/implementations.html?highlight=orphan#orphan-rules>
 
 error[E0116]: cannot define inherent `impl` for a type outside of the crate where the type is defined
  --> $DIR/no-attr-empty-impl.rs:10:1
  |
 LL | impl extern_crate::EnumWithAttr {}
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl for type defined outside of crate
  |
- = note: define and implement a trait or new type instead
+ = help: consider defining a trait and implementing it for the type or using a newtype wrapper like `struct MyType(ExternalType);` and implement it
+ = note: For more details about orphan rules, see <https://doc.rust-lang.org/reference/items/implementations.html?highlight=orphan#orphan-rules>
 
 error[E0116]: cannot define inherent `impl` for a type outside of the crate where the type is defined
  --> $DIR/no-attr-empty-impl.rs:13:1
  |
 LL | impl extern_crate::EnumNoAttr {}
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl for type defined outside of crate
  |
- = note: define and implement a trait or new type instead
+ = help: consider defining a trait and implementing it for the type or using a newtype wrapper like `struct MyType(ExternalType);` and implement it
+ = note: For more details about orphan rules, see <https://doc.rust-lang.org/reference/items/implementations.html?highlight=orphan#orphan-rules>
 
 error[E0390]: cannot define inherent `impl` for primitive types
  --> $DIR/no-attr-empty-impl.rs:16:1

tests/ui/incoherent-inherent-impls/no-other-unrelated-errors.stderr

@@ -4,7 +4,8 @@ error[E0116]: cannot define inherent `impl` for a type outside of the crate wher
 LL | impl Vec<usize> {}
  | ^^^^^^^^^^^^^^^ impl for type defined outside of crate
  |
- = note: define and implement a trait or new type instead
+ = help: consider defining a trait and implementing it for the type or using a newtype wrapper like `struct MyType(ExternalType);` and implement it
+ = note: For more details about orphan rules, see <https://doc.rust-lang.org/reference/items/implementations.html?highlight=orphan#orphan-rules>
 
 error: aborting due to 1 previous error
 

tests/ui/traits/trait-or-new-type-instead.stderr

@@ -4,7 +4,8 @@ error[E0116]: cannot define inherent `impl` for a type outside of the crate wher
 LL | impl<T> Option<T> {
  | ^^^^^^^^^^^^^^^^^ impl for type defined outside of crate
  |
- = note: define and implement a trait or new type instead
+ = help: consider defining a trait and implementing it for the type or using a newtype wrapper like `struct MyType(ExternalType);` and implement it
+ = note: For more details about orphan rules, see <https://doc.rust-lang.org/reference/items/implementations.html?highlight=orphan#orphan-rules>
 
 error: aborting due to 1 previous error