Emit an error when RTN is used with ty/ct params

compiler/rustc_hir_analysis/src/errors.rs

@@ -857,3 +857,21 @@ pub(crate) enum DropImplPolarity {
         span: Span,
     },
 }
+
+#[derive(Diagnostic)]
+pub(crate) enum ReturnTypeNotationIllegalParam {
+    #[diag(hir_analysis_return_type_notation_illegal_param_type)]
+    Type {
+        #[primary_span]
+        span: Span,
+        #[label]
+        param_span: Span,
+    },
+    #[diag(hir_analysis_return_type_notation_illegal_param_const)]
+    Const {
+        #[primary_span]
+        span: Span,
+        #[label]
+        param_span: Span,
+    },
+}