DoIt

compiler/rustc_error_messages/locales/en-US/hir_analysis.ftl

@@ -146,3 +146,5 @@ hir_analysis_const_impl_for_non_const_trait =
 
 hir_analysis_const_bound_for_non_const_trait =
     ~const can only be applied to `#[const_trait]` traits
+
+hir_analysis_self_in_impl_self = `Self` is not valid at this location

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -319,7 +319,37 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                     }
                 }
                 ItemKind::TyAlias(self_ty, _) => icx.to_ty(self_ty),
-                ItemKind::Impl(hir::Impl { self_ty, .. }) => icx.to_ty(*self_ty),
+                ItemKind::Impl(
+                    hir::Impl { self_ty, .. }
+                ) => {
+                    struct MyVisitor(bool);
+                    impl<'v> hir::intravisit::Visitor<'v> for MyVisitor {
+                        fn visit_ty(&mut self, t: &'v Ty<'v>) {
+                            if matches!(
+                                &t.kind,
+                                TyKind::Path(hir::QPath::Resolved(
+                                    _,
+                                    Path {
+                                        res: hir::def::Res::SelfTyAlias { .. },
+                                        ..
+                                    },
+                                ))
+                            ) {
+                                self.0 = true;
+                                return;
+                            }
+                            hir::intravisit::walk_ty(self, t);
+                        }
+                    }
+
+                    let mut my_visitor = MyVisitor(false);
+                    my_visitor.visit_ty(self_ty);
+
+                    match my_visitor.0 {
+                        true => { tcx.sess.emit_err(crate::errors::SelfInImplSelf { span: self_ty.span}); tcx.ty_error() },
+                        false => icx.to_ty(*self_ty),
+                    }
+                },
                 ItemKind::Fn(..) => {
                     let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
                     tcx.mk_fn_def(def_id.to_def_id(), substs)

compiler/rustc_hir_analysis/src/errors.rs

@@ -270,3 +270,10 @@ pub struct ConstBoundForNonConstTrait {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_self_in_impl_self)]
+pub struct SelfInImplSelf {
+    #[primary_span]
+    pub span: Span,
+}

src/test/ui/resolve/issue-23305.rs

@@ -3,6 +3,6 @@ pub trait ToNbt<T> {
 }
 
 impl dyn ToNbt<Self> {}
-//~^ ERROR cycle detected
+//~^ ERROR `Self` is not valid at this location
 
 fn main() {}

src/test/ui/resolve/issue-23305.stderr

@@ -1,22 +1,8 @@
-error[E0391]: cycle detected when computing type of `<impl at $DIR/issue-23305.rs:5:1: 5:21>`
+error: `Self` is not valid at this location
-  --> $DIR/issue-23305.rs:5:16
+  --> $DIR/issue-23305.rs:5:6
    |
 LL | impl dyn ToNbt<Self> {}
-   |                ^^^^
+   |      ^^^^^^^^^^^^^^^
-   |
-   = note: ...which immediately requires computing type of `<impl at $DIR/issue-23305.rs:5:1: 5:21>` again
-note: cycle used when collecting item types in top-level module
-  --> $DIR/issue-23305.rs:1:1
-   |
-LL | / pub trait ToNbt<T> {
-LL | |     fn new(val: T) -> Self;
-LL | | }
-LL | |
-...  |
-LL | |
-LL | | fn main() {}
-   | |____________^
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0391`.

src/test/ui/resolve/resolve-self-in-impl.rs

@@ -11,10 +11,10 @@ impl Tr for S where Self: Copy {} // OK
 impl Tr for S where S<Self>: Copy {} // OK
 impl Tr for S where Self::A: Copy {} // OK
 
-impl Tr for Self {} //~ ERROR cycle detected
+impl Tr for Self {} //~ ERROR `Self` is not valid at this location
-impl Tr for S<Self> {} //~ ERROR cycle detected
+impl Tr for S<Self> {} //~ ERROR `Self` is not valid at this location
-impl Self {} //~ ERROR cycle detected
+impl Self {} //~ ERROR `Self` is not valid at this location
-impl S<Self> {} //~ ERROR cycle detected
+impl S<Self> {} //~ ERROR `Self` is not valid at this location
 impl Tr<Self::A> for S {} //~ ERROR cycle detected
 
 fn main() {}

src/test/ui/resolve/resolve-self-in-impl.stderr

@@ -1,78 +1,26 @@
-error[E0391]: cycle detected when computing type of `<impl at $DIR/resolve-self-in-impl.rs:14:1: 14:17>`
+error: `Self` is not valid at this location
   --> $DIR/resolve-self-in-impl.rs:14:13
    |
 LL | impl Tr for Self {}
    |             ^^^^
-   |
-   = note: ...which immediately requires computing type of `<impl at $DIR/resolve-self-in-impl.rs:14:1: 14:17>` again
-note: cycle used when collecting item types in top-level module
-  --> $DIR/resolve-self-in-impl.rs:1:1
-   |
-LL | / #![feature(associated_type_defaults)]
-LL | |
-LL | | struct S<T = u8>(T);
-LL | | trait Tr<T = u8> {
-...  |
-LL | |
-LL | | fn main() {}
-   | |____________^
 
-error[E0391]: cycle detected when computing type of `<impl at $DIR/resolve-self-in-impl.rs:15:1: 15:20>`
+error: `Self` is not valid at this location
-  --> $DIR/resolve-self-in-impl.rs:15:15
+  --> $DIR/resolve-self-in-impl.rs:15:13
    |
 LL | impl Tr for S<Self> {}
-   |               ^^^^
+   |             ^^^^^^^
-   |
-   = note: ...which immediately requires computing type of `<impl at $DIR/resolve-self-in-impl.rs:15:1: 15:20>` again
-note: cycle used when collecting item types in top-level module
-  --> $DIR/resolve-self-in-impl.rs:1:1
-   |
-LL | / #![feature(associated_type_defaults)]
-LL | |
-LL | | struct S<T = u8>(T);
-LL | | trait Tr<T = u8> {
-...  |
-LL | |
-LL | | fn main() {}
-   | |____________^
 
-error[E0391]: cycle detected when computing type of `<impl at $DIR/resolve-self-in-impl.rs:16:1: 16:10>`
+error: `Self` is not valid at this location
   --> $DIR/resolve-self-in-impl.rs:16:6
    |
 LL | impl Self {}
    |      ^^^^
-   |
-   = note: ...which immediately requires computing type of `<impl at $DIR/resolve-self-in-impl.rs:16:1: 16:10>` again
-note: cycle used when collecting item types in top-level module
-  --> $DIR/resolve-self-in-impl.rs:1:1
-   |
-LL | / #![feature(associated_type_defaults)]
-LL | |
-LL | | struct S<T = u8>(T);
-LL | | trait Tr<T = u8> {
-...  |
-LL | |
-LL | | fn main() {}
-   | |____________^
 
-error[E0391]: cycle detected when computing type of `<impl at $DIR/resolve-self-in-impl.rs:17:1: 17:13>`
+error: `Self` is not valid at this location
-  --> $DIR/resolve-self-in-impl.rs:17:8
+  --> $DIR/resolve-self-in-impl.rs:17:6
    |
 LL | impl S<Self> {}
-   |        ^^^^
+   |      ^^^^^^^
-   |
-   = note: ...which immediately requires computing type of `<impl at $DIR/resolve-self-in-impl.rs:17:1: 17:13>` again
-note: cycle used when collecting item types in top-level module
-  --> $DIR/resolve-self-in-impl.rs:1:1
-   |
-LL | / #![feature(associated_type_defaults)]
-LL | |
-LL | | struct S<T = u8>(T);
-LL | | trait Tr<T = u8> {
-...  |
-LL | |
-LL | | fn main() {}
-   | |____________^
 
 error[E0391]: cycle detected when computing trait implemented by `<impl at $DIR/resolve-self-in-impl.rs:18:1: 18:23>`
   --> $DIR/resolve-self-in-impl.rs:18:1