add error message when #[naked] is used with #[test]

compiler/rustc_builtin_macros/messages.ftl

@@ -216,6 +216,11 @@ builtin_macros_multiple_defaults = multiple declared defaults
     .note = only one variant can be default
     .suggestion = make `{$ident}` default
 
+builtin_macros_naked_functions_testing_attribute =
+    cannot use `#[naked]` with testing attributes
+    .label = function marked with testing attribute here
+    .naked_attribute = `#[naked]` is incompatible with testing attributes
+
 builtin_macros_no_default_variant = no default declared
     .help = make a unit variant default by placing `#[default]` above it
     .suggestion = make `{$ident}` default

compiler/rustc_builtin_macros/src/errors.rs

@@ -912,3 +912,13 @@ pub(crate) struct ExpectedItem<'a> {
     pub span: Span,
     pub token: &'a str,
 }
+
+#[derive(Diagnostic)]
+#[diag(builtin_macros_naked_functions_testing_attribute, code = E0798)]
+pub struct NakedFunctionTestingAttribute {
+    #[primary_span]
+    #[label(builtin_macros_naked_attribute)]
+    pub naked_span: Span,
+    #[label]
+    pub testing_span: Span,
+}

compiler/rustc_builtin_macros/src/test.rs

@@ -133,6 +133,14 @@ pub(crate) fn expand_test_or_bench(
         };
     };
 
+    if let Some(attr) = attr::find_by_name(&item.attrs, sym::naked) {
+        cx.dcx().emit_err(errors::NakedFunctionTestingAttribute {
+            testing_span: attr_sp,
+            naked_span: attr.span,
+        });
+        return vec![Annotatable::Item(item)];
+    }
+
     // check_*_signature will report any errors in the type so compilation
     // will fail. We shouldn't try to expand in this case because the errors
     // would be spurious.

compiler/rustc_error_codes/src/error_codes/E0798.md

@@ -0,0 +1,14 @@
+Testing attributes cannot be applied to functions marked with `#[naked]`.
+
+Erroneous code example:
+
+```ignore (requires test runner)
+#[test]
+#[should_panic]
+#[naked]
+fn foo() {}
+```
+
+See [the reference page for testing attributes] for more information.
+
+[the reference page for testing attributes]: https://doc.rust-lang.org/reference/attributes/testing.html

compiler/rustc_error_codes/src/lib.rs

@@ -536,6 +536,7 @@ E0794: 0794,
 E0795: 0795,
 E0796: 0796,
 E0797: 0797,
+E0798: 0798,
         );
     )
 }