Suggest using integration tests for proc-macros

compiler/rustc_resolve/src/errors.rs

@@ -508,3 +508,12 @@ pub(crate) struct RemoveSurroundingDerive {
 pub(crate) struct AddAsNonDerive<'a> {
     pub(crate) macro_path: &'a str,
 }
+
+#[derive(Diagnostic)]
+#[diag(resolve_proc_macro_same_crate)]
+pub(crate) struct ProcMacroSameCrate {
+    #[primary_span]
+    pub(crate) span: Span,
+    #[help]
+    pub(crate) is_test: bool,
+}