Migrate 'cast enum with drop to int' diagnostic

compiler/rustc_hir_typeck/messages.ftl

@@ -21,6 +21,8 @@ hir_typeck_cannot_cast_to_bool = cannot cast `{$expr_ty}` as `bool`
     .help = compare with zero instead
     .label = unsupported cast
 
+hir_typeck_cast_enum_drop = cannot cast enum `{$expr_ty}` into integer `{$cast_ty}` because it implements `Drop`
+
 hir_typeck_cast_unknown_pointer = cannot cast {$to ->
     [true] to
     *[false] from

compiler/rustc_hir_typeck/src/cast.rs

@@ -33,7 +33,7 @@
 use crate::errors;
 use crate::type_error_struct;
 use hir::ExprKind;
-use rustc_errors::{Applicability, DelayDm, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
+use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::mir::Mutability;
@@ -935,17 +935,17 @@ fn cenum_impl_drop_lint(&self, fcx: &FnCtxt<'a, 'tcx>) {
         if let ty::Adt(d, _) = self.expr_ty.kind()
             && d.has_dtor(fcx.tcx)
         {
-            fcx.tcx.struct_span_lint_hir(
+            let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);
+            let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
+
+            fcx.tcx.emit_spanned_lint(
                 lint::builtin::CENUM_IMPL_DROP_CAST,
                 self.expr.hir_id,
                 self.span,
-                DelayDm(|| format!(
+                errors::CastEnumDrop {
-                    "cannot cast enum `{}` into integer `{}` because it implements `Drop`",
+                    expr_ty,
-                    self.expr_ty, self.cast_ty
+                    cast_ty,
-                )),
+                }
-                |lint| {
-                    lint
-                },
             );
         }
     }

compiler/rustc_hir_typeck/src/errors.rs

@@ -574,6 +574,13 @@ pub struct CannotCastToBool<'tcx> {
     pub help: CannotCastToBoolHelp,
 }
 
+#[derive(LintDiagnostic)]
+#[diag(hir_typeck_cast_enum_drop)]
+pub struct CastEnumDrop<'tcx> {
+    pub expr_ty: Ty<'tcx>,
+    pub cast_ty: Ty<'tcx>,
+}
+
 #[derive(Diagnostic)]
 #[diag(hir_typeck_cast_unknown_pointer, code = "E0641")]
 pub struct CastUnknownPointer {