Suggest imports of unresolved macros

compiler/rustc_resolve/src/diagnostics.rs

@@ -929,6 +929,17 @@ impl<'a> Resolver<'a> {
         );
         self.add_typo_suggestion(err, suggestion, ident.span);
 
+        let import_suggestions = self.lookup_import_candidates(
+            ident,
+            Namespace::MacroNS,
+            parent_scope,
+            |res| match res {
+                Res::Def(DefKind::Macro(MacroKind::Bang), _) => true,
+                _ => false,
+            },
+        );
+        show_candidates(err, None, &import_suggestions, false, true);
+
         if macro_kind == MacroKind::Derive && (ident.name == sym::Send || ident.name == sym::Sync) {
             let msg = format!("unsafe traits like `{}` should be implemented explicitly", ident);
             err.span_note(ident.span, &msg);

src/test/ui/empty/empty-macro-use.stderr

@@ -3,6 +3,9 @@ error: cannot find macro `macro_two` in this scope
    |
 LL |     macro_two!();
    |     ^^^^^^^^^
+   |
+   = note: consider importing this macro:
+           two_macros::macro_two
 
 error: aborting due to previous error
 

src/test/ui/hygiene/no_implicit_prelude-2018.stderr

@@ -3,6 +3,9 @@ error: cannot find macro `print` in this scope
    |
 LL |         print!();
    |         ^^^^^
+   |
+   = note: consider importing this macro:
+           std::print
 
 error: aborting due to previous error
 

src/test/ui/hygiene/no_implicit_prelude.stderr

@@ -4,6 +4,9 @@ error: cannot find macro `panic` in this scope
 LL |         assert_eq!(0, 0);
    |         ^^^^^^^^^^^^^^^^^
    |
+   = note: consider importing one of these items:
+           core::panic
+           std::panic
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0433]: failed to resolve: use of undeclared type `Vec`

src/test/ui/macros/macro-use-wrong-name.stderr

@@ -8,6 +8,9 @@ LL |     macro_two!();
    |
 LL | macro_rules! macro_one { () => ("one") }
    | ---------------------- similarly named macro `macro_one` defined here
+   |
+   = note: consider importing this macro:
+           two_macros::macro_two
 
 error: aborting due to previous error
 

src/test/ui/missing/missing-macro-use.stderr

@@ -3,6 +3,9 @@ error: cannot find macro `macro_two` in this scope
    |
 LL |     macro_two!();
    |     ^^^^^^^^^
+   |
+   = note: consider importing this macro:
+           two_macros::macro_two
 
 error: aborting due to previous error