use proper spans

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

@@ -147,4 +147,6 @@ 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
+hir_analysis_self_in_impl_self = 
+    `Self` is not valid in the self type of an impl block
+    .note = replace `Self` with a different type

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -322,7 +322,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                 ItemKind::Impl(
                     hir::Impl { self_ty, .. }
                 ) => {
-                    struct MyVisitor(bool);
+                    struct MyVisitor(Vec<Span>);
                     impl<'v> hir::intravisit::Visitor<'v> for MyVisitor {
                         fn visit_ty(&mut self, t: &'v Ty<'v>) {
                             if matches!(
@@ -335,19 +335,22 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                                     },
                                 ))
                             ) {
-                                self.0 = true;
+                                self.0.push(t.span);
                                 return;
                             }
                             hir::intravisit::walk_ty(self, t);
                         }
                     }
 
-                    let mut my_visitor = MyVisitor(false);
+                    let mut my_visitor = MyVisitor(vec![]);
                     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() },
+                        spans if spans.len() > 0 => { 
-                        false => icx.to_ty(*self_ty),
+                            tcx.sess.emit_err(crate::errors::SelfInImplSelf { span: spans.into(), note: (), });
+                            tcx.ty_error() 
+                        },
+                        _ => icx.to_ty(*self_ty),
                     }
                 },
                 ItemKind::Fn(..) => {

compiler/rustc_hir_analysis/src/errors.rs

@@ -1,7 +1,7 @@
 //! Errors emitted by `rustc_hir_analysis`.
 
-use rustc_errors::IntoDiagnostic;
 use rustc_errors::{error_code, Applicability, DiagnosticBuilder, ErrorGuaranteed, Handler};
+use rustc_errors::{IntoDiagnostic, MultiSpan};
 use rustc_macros::{Diagnostic, LintDiagnostic};
 use rustc_middle::ty::Ty;
 use rustc_span::{symbol::Ident, Span, Symbol};
@@ -275,5 +275,7 @@ pub struct ConstBoundForNonConstTrait {
 #[diag(hir_analysis_self_in_impl_self)]
 pub struct SelfInImplSelf {
     #[primary_span]
-    pub span: Span,
+    pub span: MultiSpan,
+    #[note]
+    pub note: (),
 }

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

@@ -3,6 +3,6 @@ pub trait ToNbt<T> {
 }
 
 impl dyn ToNbt<Self> {}
-//~^ ERROR `Self` is not valid at this location
+//~^ ERROR `Self` is not valid in the self type of an impl block
 
 fn main() {}

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

@@ -1,8 +1,10 @@
-error: `Self` is not valid at this location
+error: `Self` is not valid in the self type of an impl block
-  --> $DIR/issue-23305.rs:5:6
+  --> $DIR/issue-23305.rs:5:16
    |
 LL | impl dyn ToNbt<Self> {}
-   |      ^^^^^^^^^^^^^^^
+   |                ^^^^
+   |
+   = note: replace `Self` with a different type
 
 error: aborting due to previous error
 

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

@@ -11,10 +11,11 @@ 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 `Self` is not valid at this location
+impl Tr for Self {} //~ ERROR `Self` is not valid in the self type of an impl block
-impl Tr for S<Self> {} //~ ERROR `Self` is not valid at this location
+impl Tr for S<Self> {} //~ ERROR `Self` is not valid in the self type of an impl block
-impl Self {} //~ ERROR `Self` is not valid at this location
+impl Self {} //~ ERROR `Self` is not valid in the self type of an impl block
-impl S<Self> {} //~ ERROR `Self` is not valid at this location
+impl S<Self> {} //~ ERROR `Self` is not valid in the self type of an impl block
+impl (Self, Self) {} //~ ERROR `Self` is not valid in the self type of an impl block
 impl Tr<Self::A> for S {} //~ ERROR cycle detected
 
 fn main() {}

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

@@ -1,34 +1,50 @@
-error: `Self` is not valid at this location
+error: `Self` is not valid in the self type of an impl block
   --> $DIR/resolve-self-in-impl.rs:14:13
    |
 LL | impl Tr for Self {}
    |             ^^^^
+   |
+   = note: replace `Self` with a different type
 
-error: `Self` is not valid at this location
+error: `Self` is not valid in the self type of an impl block
-  --> $DIR/resolve-self-in-impl.rs:15:13
+  --> $DIR/resolve-self-in-impl.rs:15:15
    |
 LL | impl Tr for S<Self> {}
-   |             ^^^^^^^
+   |               ^^^^
+   |
+   = note: replace `Self` with a different type
 
-error: `Self` is not valid at this location
+error: `Self` is not valid in the self type of an impl block
   --> $DIR/resolve-self-in-impl.rs:16:6
    |
 LL | impl Self {}
    |      ^^^^
+   |
+   = note: replace `Self` with a different type
 
-error: `Self` is not valid at this location
+error: `Self` is not valid in the self type of an impl block
-  --> $DIR/resolve-self-in-impl.rs:17:6
+  --> $DIR/resolve-self-in-impl.rs:17:8
    |
 LL | impl S<Self> {}
-   |      ^^^^^^^
+   |        ^^^^
+   |
+   = note: replace `Self` with a different type
 
-error[E0391]: cycle detected when computing trait implemented by `<impl at $DIR/resolve-self-in-impl.rs:18:1: 18:23>`
+error: `Self` is not valid in the self type of an impl block
-  --> $DIR/resolve-self-in-impl.rs:18:1
+  --> $DIR/resolve-self-in-impl.rs:18:7
+   |
+LL | impl (Self, Self) {}
+   |       ^^^^  ^^^^
+   |
+   = note: replace `Self` with a different type
+
+error[E0391]: cycle detected when computing trait implemented by `<impl at $DIR/resolve-self-in-impl.rs:19:1: 19:23>`
+  --> $DIR/resolve-self-in-impl.rs:19:1
    |
 LL | impl Tr<Self::A> for S {}
    | ^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: ...which immediately requires computing trait implemented by `<impl at $DIR/resolve-self-in-impl.rs:18:1: 18:23>` again
+   = note: ...which immediately requires computing trait implemented by `<impl at $DIR/resolve-self-in-impl.rs:19:1: 19:23>` again
 note: cycle used when collecting item types in top-level module
   --> $DIR/resolve-self-in-impl.rs:1:1
    |
@@ -41,6 +57,6 @@ LL | |
 LL | | fn main() {}
    | |____________^
 
-error: aborting due to 5 previous errors
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0391`.