Auto merge of rust-lang#112239 - jieyouxu:targeted-no-method-suggestions, r=cjgillot

Add `#[rustc_confusables]` attribute to allow targeted "no method" error suggestions on standard library types

After this PR, the standard library developer can annotate methods on e.g. `BTreeSet::push` with `#[rustc_confusables("insert")]`. When the user mistypes `btreeset.push()`, `BTreeSet::insert` will be suggested if there are no other candidates to suggest. This PR lays the foundations for contributors to add `rustc_confusables` annotations to standard library types for targeted suggestions, as specified in rust-lang#59450, or to address cases such as rust-lang#108437.

### Example

Assume `BTreeSet` is the standard library type:

```
// Standard library definition
#![feature(rustc_attrs)]

struct BTreeSet;

impl BTreeSet {
    #[rustc_confusables("push")]
    fn insert(&self) {}
}

// User code
fn main() {
    let x = BTreeSet {};
    x.push();
}
```

A new suggestion (which has lower precedence than suggestions for misspellings and only is shown when there are no misspellings suggestions) will be added to hint the user maybe they intended to write `x.insert()` instead:

```
error[E0599]: no method named `push` found for struct `BTreeSet` in the current scope
  --> test.rs:12:7
   |
3  | struct BTreeSet;
   | --------------- method `push` not found for this struct
...
12 |     x.push();
   |       ^^^^ method not found in `BTreeSet`
   |
help: you might have meant to use `insert`
   |
12 |     x.insert();
   |       ~~~~~~

error: aborting due to previous error
```

Author: bors

Cargo.lock

@@ -3665,6 +3665,7 @@ name = "rustc_hir_typeck"
 version = "0.1.0"
 dependencies = [
  "rustc_ast",
+ "rustc_attr",
  "rustc_data_structures",
  "rustc_errors",
  "rustc_fluent_macro",

compiler/rustc_attr/src/builtin.rs

@@ -1217,3 +1217,20 @@ pub fn parse_alignment(node: &ast::LitKind) -> Result<u32, &'static str> {
         Err("not an unsuffixed integer")
     }
 }
+
+/// Read the content of a `rustc_confusables` attribute, and return the list of candidate names.
+pub fn parse_confusables(attr: &Attribute) -> Option<Vec<Symbol>> {
+    let meta = attr.meta()?;
+    let MetaItem { kind: MetaItemKind::List(ref metas), .. } = meta else { return None };
+
+    let mut candidates = Vec::new();
+
+    for meta in metas {
+        let NestedMetaItem::Lit(meta_lit) = meta else {
+            return None;
+        };
+        candidates.push(meta_lit.symbol);
+    }
+
+    return Some(candidates);
+}

compiler/rustc_feature/src/builtin_attrs.rs

@@ -625,6 +625,12 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         ErrorFollowing,
         INTERNAL_UNSTABLE
     ),
+    rustc_attr!(
+        rustc_confusables, Normal,
+        template!(List: r#""name1", "name2", ..."#),
+        ErrorFollowing,
+        INTERNAL_UNSTABLE,
+    ),
     // Enumerates "identity-like" conversion methods to suggest on type mismatch.
     rustc_attr!(
         rustc_conversion_suggestion, Normal, template!(Word), WarnFollowing, INTERNAL_UNSTABLE

compiler/rustc_hir_typeck/Cargo.toml

@@ -9,6 +9,7 @@ edition = "2021"
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
 tracing = "0.1"
 rustc_ast = { path = "../rustc_ast" }
+rustc_attr = { path = "../rustc_attr" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_graphviz = { path = "../rustc_graphviz" }

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -2,13 +2,12 @@
 //! found or is otherwise invalid.
 
 use crate::errors;
-use crate::errors::CandidateTraitNote;
-use crate::errors::NoAssociatedItem;
+use crate::errors::{CandidateTraitNote, NoAssociatedItem};
 use crate::Expectation;
 use crate::FnCtxt;
 use rustc_ast::ast::Mutability;
-use rustc_data_structures::fx::FxIndexMap;
-use rustc_data_structures::fx::FxIndexSet;
+use rustc_attr::parse_confusables;
+use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::unord::UnordSet;
 use rustc_errors::StashKey;
 use rustc_errors::{
@@ -1038,6 +1037,28 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             "the {item_kind} was found for\n{}{}",
                             type_candidates, additional_types
                         ));
+                    } else {
+                        'outer: for inherent_impl_did in self.tcx.inherent_impls(adt.did()) {
+                            for inherent_method in
+                                self.tcx.associated_items(inherent_impl_did).in_definition_order()
+                            {
+                                if let Some(attr) = self.tcx.get_attr(inherent_method.def_id, sym::rustc_confusables)
+                                    && let Some(candidates) = parse_confusables(attr)
+                                    && candidates.contains(&item_name.name)
+                                {
+                                    err.span_suggestion_verbose(
+                                        item_name.span,
+                                        format!(
+                                            "you might have meant to use `{}`",
+                                            inherent_method.name.as_str()
+                                        ),
+                                        inherent_method.name.as_str(),
+                                        Applicability::MaybeIncorrect,
+                                    );
+                                    break 'outer;
+                                }
+                            }
+                        }
                     }
                 }
             } else {

compiler/rustc_passes/messages.ftl

@@ -98,6 +98,9 @@ passes_collapse_debuginfo =
     `collapse_debuginfo` attribute should be applied to macro definitions
     .label = not a macro definition
 
+passes_confusables = attribute should be applied to an inherent method
+    .label = not an inherent method
+
 passes_const_impl_const_trait =
     const `impl`s must be for traits marked with `#[const_trait]`
     .note = this trait must be annotated with `#[const_trait]`
@@ -266,6 +269,9 @@ passes_duplicate_lang_item_crate_depends =
     .first_definition_path = first definition in `{$orig_crate_name}` loaded from {$orig_path}
     .second_definition_path = second definition in `{$crate_name}` loaded from {$path}
 
+passes_empty_confusables =
+    expected at least one confusable name
+
 passes_export_name =
     attribute should be applied to a free function, impl method or static
     .label = not a free function, impl method or static
@@ -326,6 +332,9 @@ passes_implied_feature_not_exist =
 passes_incorrect_do_not_recommend_location =
     `#[do_not_recommend]` can only be placed on trait implementations
 
+passes_incorrect_meta_item = expected a quoted string literal
+passes_incorrect_meta_item_suggestion = consider surrounding this with quotes
+
 passes_incorrect_target =
     `{$name}` language item must be applied to a {$kind} with {$at_least ->
         [true] at least {$num}

compiler/rustc_passes/src/check_attr.rs

@@ -183,6 +183,7 @@ impl CheckAttrVisitor<'_> {
                 | sym::rustc_allowed_through_unstable_modules
                 | sym::rustc_promotable => self.check_stability_promotable(&attr, span, target),
                 sym::link_ordinal => self.check_link_ordinal(&attr, span, target),
+                sym::rustc_confusables => self.check_confusables(&attr, target),
                 _ => true,
             };
 
@@ -1985,6 +1986,46 @@ impl CheckAttrVisitor<'_> {
         }
     }
 
+    fn check_confusables(&self, attr: &Attribute, target: Target) -> bool {
+        match target {
+            Target::Method(MethodKind::Inherent) => {
+                let Some(meta) = attr.meta() else {
+                    return false;
+                };
+                let ast::MetaItem { kind: MetaItemKind::List(ref metas), .. } = meta else {
+                    return false;
+                };
+
+                let mut candidates = Vec::new();
+
+                for meta in metas {
+                    let NestedMetaItem::Lit(meta_lit) = meta else {
+                        self.tcx.sess.emit_err(errors::IncorrectMetaItem {
+                            span: meta.span(),
+                            suggestion: errors::IncorrectMetaItemSuggestion {
+                                lo: meta.span().shrink_to_lo(),
+                                hi: meta.span().shrink_to_hi(),
+                            },
+                        });
+                        return false;
+                    };
+                    candidates.push(meta_lit.symbol);
+                }
+
+                if candidates.is_empty() {
+                    self.tcx.sess.emit_err(errors::EmptyConfusables { span: attr.span });
+                    return false;
+                }
+
+                true
+            }
+            _ => {
+                self.tcx.sess.emit_err(errors::Confusables { attr_span: attr.span });
+                false
+            }
+        }
+    }
+
     fn check_deprecated(&self, hir_id: HirId, attr: &Attribute, _span: Span, target: Target) {
         match target {
             Target::Closure | Target::Expression | Target::Statement | Target::Arm => {

compiler/rustc_passes/src/errors.rs

@@ -617,6 +617,38 @@ pub struct LinkOrdinal {
     pub attr_span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(passes_confusables)]
+pub struct Confusables {
+    #[primary_span]
+    pub attr_span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(passes_empty_confusables)]
+pub(crate) struct EmptyConfusables {
+    #[primary_span]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
+#[diag(passes_incorrect_meta_item, code = "E0539")]
+pub(crate) struct IncorrectMetaItem {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub suggestion: IncorrectMetaItemSuggestion,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(passes_incorrect_meta_item_suggestion, applicability = "maybe-incorrect")]
+pub(crate) struct IncorrectMetaItemSuggestion {
+    #[suggestion_part(code = "\"")]
+    pub lo: Span,
+    #[suggestion_part(code = "\"")]
+    pub hi: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(passes_stability_promotable)]
 pub struct StabilityPromotable {

compiler/rustc_span/src/symbol.rs

@@ -1265,6 +1265,7 @@ symbols! {
         rustc_clean,
         rustc_coherence_is_core,
         rustc_coinductive,
+        rustc_confusables,
         rustc_const_stable,
         rustc_const_unstable,
         rustc_conversion_suggestion,

tests/ui/attributes/auxiliary/rustc_confusables_across_crate.rs

@@ -0,0 +1,11 @@
+#![feature(rustc_attrs)]
+
+pub struct BTreeSet;
+
+impl BTreeSet {
+    #[rustc_confusables("push", "test_b")]
+    pub fn insert(&self) {}
+
+    #[rustc_confusables("pulled")]
+    pub fn pull(&self) {}
+}