Adjust #[macro_export]/doctest help suggestion for non_local_defs lint

compiler/rustc_lint/messages.ftl

@@ -456,6 +456,8 @@ lint_non_local_definitions_macro_rules = non-local `macro_rules!` definition, th
             [one] `{$body_name}`
            *[other] `{$body_name}` and up {$depth} bodies
         }
+    .help_doctest =
+        remove the `#[macro_export]` or make this doc-test a standalone test with its own `fn main() {"{"} ... {"}"}`
     .non_local = a `macro_rules!` definition is non-local if it is nested inside an item and has a `#[macro_export]` attribute
     .exception = one exception to the rule are anon-const (`const _: () = {"{"} ... {"}"}`) at top-level module
 

compiler/rustc_lint/src/lints.rs

@@ -1350,14 +1350,18 @@ pub enum NonLocalDefinitionsDiag {
         const_anon: Option<Span>,
     },
     #[diag(lint_non_local_definitions_macro_rules)]
-    #[help]
-    #[note(lint_non_local)]
-    #[note(lint_exception)]
-    #[note(lint_non_local_definitions_deprecation)]
     MacroRules {
         depth: u32,
         body_kind_descr: &'static str,
         body_name: String,
+        #[help]
+        help: Option<()>,
+        #[help(lint_help_doctest)]
+        doctest_help: Option<()>,
+        #[note(lint_non_local)]
+        #[note(lint_exception)]
+        #[note(lint_non_local_definitions_deprecation)]
+        notes: (),
         #[subdiagnostic]
         cargo_update: Option<NonLocalDefinitionsCargoUpdateNote>,
     },

compiler/rustc_lint/src/non_local_def.rs

@@ -232,6 +232,12 @@ impl<'tcx> LateLintPass<'tcx> for NonLocalDefinitions {
             ItemKind::Macro(_macro, MacroKind::Bang)
                 if cx.tcx.has_attr(item.owner_id.def_id, sym::macro_export) =>
             {
+                // determining we if are in a doctest context can't currently be determined
+                // by the code it-self (no specific attrs), but fortunatly rustdoc sets a
+                // perma-unstable env for libtest so we just re-use that env for now
+                let is_at_toplevel_doctest =
+                    self.body_depth == 2 && std::env::var("UNSTABLE_RUSTDOC_TEST_PATH").is_ok();
+
                 cx.emit_span_lint(
                     NON_LOCAL_DEFINITIONS,
                     item.span,
@@ -242,6 +248,9 @@ impl<'tcx> LateLintPass<'tcx> for NonLocalDefinitions {
                             .map(|s| s.to_ident_string())
                             .unwrap_or_else(|| "<unnameable>".to_string()),
                         cargo_update: cargo_update(),
+                        help: (!is_at_toplevel_doctest).then_some(()),
+                        doctest_help: is_at_toplevel_doctest.then_some(()),
+                        notes: (),
                     },
                 )
             }