Consider doc(alias) when providing typo suggestions

This means that

```rust
impl Foo {
    #[doc(alias = "quux")]
    fn bar(&self) {}
}

fn main() {
    (Foo {}).quux();
}
```

will suggest `bar`. This currently uses the "there is a method with a
similar name" help text, because the point where we choose and emit a
suggestion is different from where we gather the suggestions. Changes
have mainly been made to the latter.

The selection code will now fall back to aliased candidates, but
generally only if there is no candidate that matches based on the
existing Levenshtein methodology.

Fixes #83968.

compiler/rustc_hir_typeck/src/method/mod.rs

@@ -76,7 +76,7 @@ pub struct NoMatchData<'tcx> {
     pub unsatisfied_predicates:
         Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>,
     pub out_of_scope_traits: Vec<DefId>,
-    pub lev_candidate: Option<ty::AssocItem>,
+    pub similar_candidate: Option<ty::AssocItem>,
     pub mode: probe::Mode,
 }
 

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -461,7 +461,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     static_candidates: Vec::new(),
                     unsatisfied_predicates: Vec::new(),
                     out_of_scope_traits: Vec::new(),
-                    lev_candidate: None,
+                    similar_candidate: None,
                     mode,
                 }));
             }
@@ -1076,13 +1076,13 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         if let Some((kind, def_id)) = private_candidate {
             return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits));
         }
-        let lev_candidate = self.probe_for_lev_candidate()?;
+        let similar_candidate = self.probe_for_similar_candidate()?;
 
         Err(MethodError::NoMatch(NoMatchData {
             static_candidates,
             unsatisfied_predicates,
             out_of_scope_traits,
-            lev_candidate,
+            similar_candidate,
             mode: self.mode,
         }))
     }
@@ -1787,7 +1787,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
     /// Similarly to `probe_for_return_type`, this method attempts to find the best matching
     /// candidate method where the method name may have been misspelled. Similarly to other
     /// Levenshtein based suggestions, we provide at most one such suggestion.
-    fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
+    fn probe_for_similar_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
         debug!("probing for method names similar to {:?}", self.method_name);
 
         let steps = self.steps.clone();
@@ -1831,6 +1831,12 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                         None,
                     )
                 }
+                .or_else(|| {
+                    applicable_close_candidates
+                        .iter()
+                        .find(|cand| self.matches_by_doc_alias(cand.def_id))
+                        .map(|cand| cand.name)
+                })
                 .unwrap();
                 Ok(applicable_close_candidates.into_iter().find(|method| method.name == best_name))
             }
@@ -1981,6 +1987,38 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         }
     }
 
+    /// Determine if the associated item withe the given DefId matches
+    /// the desired name via a doc alias.
+    fn matches_by_doc_alias(&self, def_id: DefId) -> bool {
+        let Some(name) = self.method_name else { return false; };
+        let Some(local_def_id) = def_id.as_local() else { return false; };
+        let hir_id = self.fcx.tcx.hir().local_def_id_to_hir_id(local_def_id);
+        let attrs = self.fcx.tcx.hir().attrs(hir_id);
+        for attr in attrs {
+            let sym::doc = attr.name_or_empty() else { continue; };
+            let Some(values) = attr.meta_item_list() else { continue; };
+            for v in values {
+                if v.name_or_empty() != sym::alias {
+                    continue;
+                }
+                if let Some(nested) = v.meta_item_list() {
+                    // #[doc(alias("foo", "bar"))]
+                    for n in nested {
+                        if let Some(lit) = n.lit() && name.as_str() == lit.symbol.as_str() {
+                            return true;
+                        }
+                    }
+                } else if let Some(meta) = v.meta_item()
+                    && let Some(lit) = meta.name_value_literal()
+                    && name.as_str() == lit.symbol.as_str() {
+                        // #[doc(alias = "foo")]
+                        return true;
+                }
+            }
+        }
+        false
+    }
+
     /// Finds the method with the appropriate name (or return type, as the case may be). If
     /// `allow_similar_names` is set, find methods with close-matching names.
     // The length of the returned iterator is nearly always 0 or 1 and this
@@ -1996,6 +2034,9 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                         if !self.is_relevant_kind_for_mode(x.kind) {
                             return false;
                         }
+                        if self.matches_by_doc_alias(x.def_id) {
+                            return true;
+                        }
                         match lev_distance_with_substrings(name.as_str(), x.name.as_str(), max_dist)
                         {
                             Some(d) => d > 0,

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -262,7 +262,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let ty_str = with_forced_trimmed_paths!(self.ty_to_string(rcvr_ty));
         let is_method = mode == Mode::MethodCall;
         let unsatisfied_predicates = &no_match_data.unsatisfied_predicates;
-        let lev_candidate = no_match_data.lev_candidate;
+        let similar_candidate = no_match_data.similar_candidate;
         let item_kind = if is_method {
             "method"
         } else if rcvr_ty.is_enum() {
@@ -937,7 +937,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // give a helping note that it has to be called as `(x.f)(...)`.
         if let SelfSource::MethodCall(expr) = source {
             if !self.suggest_calling_field_as_fn(span, rcvr_ty, expr, item_name, &mut err)
-                && lev_candidate.is_none()
+                && similar_candidate.is_none()
                 && !custom_span_label
             {
                 label_span_not_found(&mut err);
@@ -1015,20 +1015,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             if fallback_span {
                 err.span_label(span, msg);
             }
-        } else if let Some(lev_candidate) = lev_candidate {
+        } else if let Some(similar_candidate) = similar_candidate {
             // Don't emit a suggestion if we found an actual method
             // that had unsatisfied trait bounds
             if unsatisfied_predicates.is_empty() {
-                let def_kind = lev_candidate.kind.as_def_kind();
+                let def_kind = similar_candidate.kind.as_def_kind();
                 // Methods are defined within the context of a struct and their first parameter is always self,
                 // which represents the instance of the struct the method is being called on
                 // Associated functions don’t take self as a parameter and
                 // they are not methods because they don’t have an instance of the struct to work with.
-                if def_kind == DefKind::AssocFn && lev_candidate.fn_has_self_parameter {
+                if def_kind == DefKind::AssocFn && similar_candidate.fn_has_self_parameter {
                     err.span_suggestion(
                         span,
                         "there is a method with a similar name",
-                        lev_candidate.name,
+                        similar_candidate.name,
                         Applicability::MaybeIncorrect,
                     );
                 } else {
@@ -1037,9 +1037,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         &format!(
                             "there is {} {} with a similar name",
                             def_kind.article(),
-                            def_kind.descr(lev_candidate.def_id),
+                            def_kind.descr(similar_candidate.def_id),
                         ),
-                        lev_candidate.name,
+                        similar_candidate.name,
                         Applicability::MaybeIncorrect,
                     );
                 }

tests/ui/methods/method-not-found-but-doc-alias.rs

@@ -0,0 +1,11 @@
+struct Foo;
+
+impl Foo {
+    #[doc(alias = "quux")]
+    fn bar(&self) {}
+}
+
+fn main() {
+    Foo.quux();
+    //~^ ERROR  no method named `quux` found for struct `Foo` in the current scope
+}

tests/ui/methods/method-not-found-but-doc-alias.stderr

@@ -0,0 +1,12 @@
+error[E0599]: no method named `quux` found for struct `Foo` in the current scope
+  --> $DIR/method-not-found-but-doc-alias.rs:9:9
+   |
+LL | struct Foo;
+   | ---------- method `quux` not found for this struct
+...
+LL |     Foo.quux();
+   |         ^^^^ help: there is a method with a similar name: `bar`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0599`.