Explicitly reject negative and reservation drop impls

compiler/rustc_hir_analysis/src/errors.rs

@@ -815,3 +815,17 @@ pub(crate) struct MissingTildeConst {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+pub(crate) enum DropImplPolarity {
+    #[diag(hir_analysis_drop_impl_negative)]
+    Negative {
+        #[primary_span]
+        span: Span,
+    },
+    #[diag(hir_analysis_drop_impl_reservation)]
+    Reservation {
+        #[primary_span]
+        span: Span,
+    },
+}