Add do_not_recommend typo help

Author: mejrs

compiler/rustc_resolve/src/macros.rs

@@ -28,7 +28,7 @@ use rustc_session::lint::builtin::{
     UNUSED_MACRO_RULES, UNUSED_MACROS,
 };
 use rustc_session::parse::feature_err;
-use rustc_span::edit_distance::edit_distance;
+use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::{self, AstPass, ExpnData, ExpnKind, LocalExpnId, MacroKind};
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, kw, sym};
@@ -652,13 +652,13 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         if res == Res::NonMacroAttr(NonMacroAttrKind::Tool)
             && let [namespace, attribute, ..] = &*path.segments
             && namespace.ident.name == sym::diagnostic
-            && !(attribute.ident.name == sym::on_unimplemented
-                || attribute.ident.name == sym::do_not_recommend)
+            && ![sym::on_unimplemented, sym::do_not_recommend].contains(&attribute.ident.name)
         {
-            let distance =
-                edit_distance(attribute.ident.name.as_str(), sym::on_unimplemented.as_str(), 5);
-
-            let typo_name = distance.map(|_| sym::on_unimplemented);
+            let typo_name = find_best_match_for_name(
+                &[sym::on_unimplemented, sym::do_not_recommend],
+                attribute.ident.name,
+                Some(5),
+            );
 
             self.tcx.sess.psess.buffer_lint(
                 UNKNOWN_OR_MALFORMED_DIAGNOSTIC_ATTRIBUTES,

src/tools/cargo

@@ -16,4 +16,9 @@ trait Y{}
 //~^^HELP an attribute with a similar name exists
 trait Z{}
 
+#[diagnostic::dont_recommend]
+//~^ERROR unknown diagnostic attribute
+//~^^HELP an attribute with a similar name exists
+impl X for u8 {}
+
 fn main(){}

tests/ui/diagnostic_namespace/suggest_typos.rs

@@ -37,5 +37,17 @@ help: an attribute with a similar name exists
 LL | #[diagnostic::on_unimplemented]
    |                  ++
 
-error: aborting due to 3 previous errors
+error: unknown diagnostic attribute
+  --> $DIR/suggest_typos.rs:19:15
+   |
+LL | #[diagnostic::dont_recommend]
+   |               ^^^^^^^^^^^^^^
+   |
+help: an attribute with a similar name exists
+   |
+LL - #[diagnostic::dont_recommend]
+LL + #[diagnostic::do_not_recommend]
+   |
+
+error: aborting due to 4 previous errors