7 files changed, 30 insertions, 78 deletions
diff --git a/compiler/rustc_hir_analysis/messages.ftl b/compiler/rustc_hir_analysis/messages.ftl
index 064d9c077b0..91b1506d1e4 100644
--- a/compiler/rustc_hir_analysis/messages.ftl
+++ b/compiler/rustc_hir_analysis/messages.ftl
@@ -55,8 +55,6 @@ hir_analysis_cannot_capture_late_bound_ty =
     cannot capture late-bound type parameter in {$what}
     .label = parameter defined here
 
-hir_analysis_cast_thin_pointer_to_fat_pointer = cannot cast thin pointer `{$expr_ty}` to fat pointer `{$cast_ty}`
-
 hir_analysis_closure_implicit_hrtb = implicit types in closure signatures are forbidden when `for<...>` is present
     .label = `for<...>` is here
 
diff --git a/compiler/rustc_hir_analysis/src/errors.rs b/compiler/rustc_hir_analysis/src/errors.rs
index 3ffb51fa992..79e948ae7d9 100644
--- a/compiler/rustc_hir_analysis/src/errors.rs
+++ b/compiler/rustc_hir_analysis/src/errors.rs
@@ -708,15 +708,6 @@ pub(crate) struct PassToVariadicFunction<'tcx, 'a> {
 }
 
 #[derive(Diagnostic)]
-#[diag(hir_analysis_cast_thin_pointer_to_fat_pointer, code = E0607)]
-pub(crate) struct CastThinPointerToFatPointer<'tcx> {
-    #[primary_span]
-    pub span: Span,
-    pub expr_ty: Ty<'tcx>,
-    pub cast_ty: String,
-}
-
-#[derive(Diagnostic)]
 #[diag(hir_analysis_invalid_union_field, code = E0740)]
 pub(crate) struct InvalidUnionField {
     #[primary_span]
diff --git a/compiler/rustc_hir_analysis/src/structured_errors.rs b/compiler/rustc_hir_analysis/src/structured_errors.rs
index 5abfd25dd95..61a2400f9e4 100644
--- a/compiler/rustc_hir_analysis/src/structured_errors.rs
+++ b/compiler/rustc_hir_analysis/src/structured_errors.rs
@@ -1,10 +1,7 @@
 mod missing_cast_for_variadic_arg;
-mod sized_unsized_cast;
 mod wrong_number_of_generic_args;
 
-pub use self::{
-    missing_cast_for_variadic_arg::*, sized_unsized_cast::*, wrong_number_of_generic_args::*,
-};
+pub use self::{missing_cast_for_variadic_arg::*, wrong_number_of_generic_args::*};
 
 use rustc_errors::{Diag, ErrCode};
 use rustc_session::Session;
diff --git a/compiler/rustc_hir_analysis/src/structured_errors/sized_unsized_cast.rs b/compiler/rustc_hir_analysis/src/structured_errors/sized_unsized_cast.rs
deleted file mode 100644
index 9e871ff9af0..00000000000
--- a/compiler/rustc_hir_analysis/src/structured_errors/sized_unsized_cast.rs
+++ /dev/null
@@ -1,56 +0,0 @@
-use crate::{errors, structured_errors::StructuredDiag};
-use rustc_errors::{codes::*, Diag};
-use rustc_middle::ty::{Ty, TypeVisitableExt};
-use rustc_session::Session;
-use rustc_span::Span;
-
-pub struct SizedUnsizedCast<'tcx> {
-    pub sess: &'tcx Session,
-    pub span: Span,
-    pub expr_ty: Ty<'tcx>,
-    pub cast_ty: String,
-}
-
-impl<'tcx> StructuredDiag<'tcx> for SizedUnsizedCast<'tcx> {
-    fn session(&self) -> &Session {
-        self.sess
-    }
-
-    fn code(&self) -> ErrCode {
-        E0607
-    }
-
-    fn diagnostic_common(&self) -> Diag<'tcx> {
-        let mut err = self.sess.dcx().create_err(errors::CastThinPointerToFatPointer {
-            span: self.span,
-            expr_ty: self.expr_ty,
-            cast_ty: self.cast_ty.to_owned(),
-        });
-
-        if self.expr_ty.references_error() {
-            err.downgrade_to_delayed_bug();
-        }
-
-        err
-    }
-
-    fn diagnostic_extended(&self, mut err: Diag<'tcx>) -> Diag<'tcx> {
-        err.help(
-            "Thin pointers are \"simple\" pointers: they are purely a reference to a
-memory address.
-
-Fat pointers are pointers referencing \"Dynamically Sized Types\" (also
-called DST). DST don't have a statically known size, therefore they can
-only exist behind some kind of pointers that contain additional
-information. Slices and trait objects are DSTs. In the case of slices,
-the additional information the fat pointer holds is their size.
-
-To fix this error, don't try to cast directly between thin and fat
-pointers.
-
-For more information about casts, take a look at The Book:
-https://doc.rust-lang.org/reference/expressions/operator-expr.html#type-cast-expressions",
-        );
-        err
-    }
-}
diff --git a/compiler/rustc_hir_typeck/messages.ftl b/compiler/rustc_hir_typeck/messages.ftl
index d6f3f4d640b..3c5070bd006 100644
--- a/compiler/rustc_hir_typeck/messages.ftl
+++ b/compiler/rustc_hir_typeck/messages.ftl
@@ -23,6 +23,21 @@ hir_typeck_cannot_cast_to_bool = cannot cast `{$expr_ty}` as `bool`
 
 hir_typeck_cast_enum_drop = cannot cast enum `{$expr_ty}` into integer `{$cast_ty}` because it implements `Drop`
 
+hir_typeck_cast_thin_pointer_to_fat_pointer = cannot cast thin pointer `{$expr_ty}` to fat pointer `{$cast_ty}`
+    .teach_help = Thin pointers are "simple" pointers: they are purely a reference to a
+        memory address.
+
+        Fat pointers are pointers referencing "Dynamically Sized Types" (also
+        called DST). DST don't have a statically known size, therefore they can
+        only exist behind some kind of pointers that contain additional
+        information. Slices and trait objects are DSTs. In the case of slices,
+        the additional information the fat pointer holds is their size.
+
+        To fix this error, don't try to cast directly between thin and fat
+        pointers.
+
+        For more information about casts, take a look at The Book:
+        https://doc.rust-lang.org/reference/expressions/operator-expr.html#type-cast-expressions",
 hir_typeck_cast_unknown_pointer = cannot cast {$to ->
     [true] to
     *[false] from
diff --git a/compiler/rustc_hir_typeck/src/cast.rs b/compiler/rustc_hir_typeck/src/cast.rs
index cb1a412d17e..53e44d6bcae 100644
--- a/compiler/rustc_hir_typeck/src/cast.rs
+++ b/compiler/rustc_hir_typeck/src/cast.rs
@@ -500,16 +500,12 @@ impl<'a, 'tcx> CastCheck<'tcx> {
                 err.emit();
             }
             CastError::SizedUnsizedCast => {
-                use rustc_hir_analysis::structured_errors::{SizedUnsizedCast, StructuredDiag};
-
-                SizedUnsizedCast {
-                    sess: fcx.tcx.sess,
+                fcx.dcx().emit_err(errors::CastThinPointerToFatPointer {
                     span: self.span,
                     expr_ty: self.expr_ty,
                     cast_ty: fcx.ty_to_string(self.cast_ty),
-                }
-                .diagnostic()
-                .emit();
+                    teach: fcx.tcx.sess.teach(E0607).then_some(()),
+                });
             }
             CastError::IntToFatCast(known_metadata) => {
                 let expr_if_nightly = fcx.tcx.sess.is_nightly_build().then_some(self.expr_span);
diff --git a/compiler/rustc_hir_typeck/src/errors.rs b/compiler/rustc_hir_typeck/src/errors.rs
index 98add86252c..e49b921e63c 100644
--- a/compiler/rustc_hir_typeck/src/errors.rs
+++ b/compiler/rustc_hir_typeck/src/errors.rs
@@ -689,3 +689,14 @@ pub struct ReplaceWithName {
     pub span: Span,
     pub name: String,
 }
+
+#[derive(Diagnostic)]
+#[diag(hir_typeck_cast_thin_pointer_to_fat_pointer, code = E0607)]
+pub(crate) struct CastThinPointerToFatPointer<'tcx> {
+    #[primary_span]
+    pub span: Span,
+    pub expr_ty: Ty<'tcx>,
+    pub cast_ty: String,
+    #[note(hir_typeck_teach_help)]
+    pub(crate) teach: Option<()>,
+}