Add infrastructure #[rustc_confusables] attribute to allow targeted

"no method" errors on standard library types

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.

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: "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/messages.ftl

@@ -50,6 +50,9 @@ hir_typeck_functional_record_update_on_non_struct =
 
 hir_typeck_help_set_edition_cargo = set `edition = "{$edition}"` in `Cargo.toml`
 hir_typeck_help_set_edition_standalone = pass `--edition {$edition}` to `rustc`
+
+hir_typeck_invalid_rustc_confusable_attr = invalid `rustc_confusable` attribute
+
 hir_typeck_lang_start_expected_sig_note = the `start` lang item should have the signature `fn(fn() -> T, isize, *const *const u8, u8) -> isize`
 
 hir_typeck_lang_start_incorrect_number_params = incorrect number of parameters for the `start` lang item

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -7,6 +7,9 @@ use crate::errors::NoAssociatedItem;
 use crate::Expectation;
 use crate::FnCtxt;
 use rustc_ast::ast::Mutability;
+use rustc_ast::token;
+use rustc_ast::tokenstream::TokenTree;
+use rustc_ast::{AttrArgs, AttrKind, Attribute, DelimArgs, NormalAttr};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::StashKey;
 use rustc_errors::{
@@ -24,6 +27,7 @@ use rustc_infer::infer::{
     type_variable::{TypeVariableOrigin, TypeVariableOriginKind},
     RegionVariableOrigin,
 };
+use rustc_macros::Diagnostic;
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
 use rustc_middle::traits::util::supertraits;
 use rustc_middle::ty::fast_reject::DeepRejectCtxt;
@@ -48,6 +52,42 @@ use rustc_hir::intravisit::Visitor;
 use std::cmp::{self, Ordering};
 use std::iter;
 
+#[derive(Debug)]
+struct ConfusablesDirective {
+    names: Vec<String>,
+}
+
+#[derive(Diagnostic)]
+#[diag(hir_typeck_invalid_rustc_confusable_attr)]
+struct ConfusablesDirectiveParseErr {
+    #[primary_span]
+    #[label]
+    span: Span,
+}
+
+impl ConfusablesDirective {
+    fn try_parse(attr: &NormalAttr) -> Result<Self, ConfusablesDirectiveParseErr> {
+        let AttrArgs::Delimited(DelimArgs { tokens, .. }) = &attr.item.args else {
+            return Err(ConfusablesDirectiveParseErr {
+                span: attr.item.span(),
+            });
+        };
+
+        let mut names = Vec::new();
+        for tok in tokens.trees() {
+            if let TokenTree::Token(tok, _) = tok
+                && let token::Token { kind, .. } = tok
+                && let token::TokenKind::Literal(lit) = kind
+                && let token::Lit { kind: token::LitKind::Str, symbol, .. } = lit
+            {
+                names.push(symbol.to_string());
+            }
+        }
+
+        Ok(ConfusablesDirective { names })
+    }
+}
+
 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     fn is_fn_ty(&self, ty: Ty<'tcx>, span: Span) -> bool {
         let tcx = self.tcx;
@@ -1026,6 +1066,44 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             "the {item_kind} was found for\n{}{}",
                             type_candidates, additional_types
                         ));
+                    } else {
+                        let mut candidate_confusable = None;
+
+                        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(Attribute { kind: AttrKind::Normal(attr), .. }) = self
+                                    .tcx
+                                    .get_attr(inherent_method.def_id, sym::rustc_confusables)
+                                {
+                                    match ConfusablesDirective::try_parse(attr) {
+                                        Ok(c) => {
+                                            if c.names.contains(&item_name.to_string()) {
+                                                candidate_confusable = Some(inherent_method);
+                                                break;
+                                            }
+                                        }
+                                        Err(e) => {
+                                            self.sess().emit_err(e);
+                                            break;
+                                        }
+                                    }
+                                }
+                            }
+                        }
+
+                        if let Some(candidate_confusable) = candidate_confusable {
+                            err.span_suggestion_verbose(
+                                item_name.span,
+                                format!(
+                                    "you might have meant to use `{}`",
+                                    candidate_confusable.name.as_str()
+                                ),
+                                candidate_confusable.name.as_str(),
+                                Applicability::MaybeIncorrect,
+                            );
+                        }
                     }
                 }
             } else {

compiler/rustc_span/src/symbol.rs

@@ -1257,6 +1257,7 @@ 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) {}
+}

tests/ui/attributes/rustc_confusables.rs

@@ -0,0 +1,20 @@
+// aux-build: rustc_confusables_across_crate.rs
+
+extern crate rustc_confusables_across_crate;
+
+use rustc_confusables_across_crate::BTreeSet;
+
+fn main() {
+    // Misspellings (similarly named methods) take precedence over `rustc_confusables`.
+    let x = BTreeSet {};
+    x.inser();
+    //~^ ERROR no method named
+    x.foo();
+    //~^ ERROR no method named
+    x.push();
+    //~^ ERROR no method named
+    x.test();
+    //~^ ERROR no method named
+    x.pulled();
+    //~^ ERROR no method named
+}

tests/ui/attributes/rustc_confusables.stderr

@@ -0,0 +1,38 @@
+error[E0599]: no method named `inser` found for struct `rustc_confusables_across_crate::BTreeSet` in the current scope
+  --> $DIR/rustc_confusables.rs:10:7
+   |
+LL |     x.inser();
+   |       ^^^^^ help: there is a method with a similar name: `insert`
+
+error[E0599]: no method named `foo` found for struct `rustc_confusables_across_crate::BTreeSet` in the current scope
+  --> $DIR/rustc_confusables.rs:12:7
+   |
+LL |     x.foo();
+   |       ^^^ method not found in `BTreeSet`
+
+error[E0599]: no method named `push` found for struct `rustc_confusables_across_crate::BTreeSet` in the current scope
+  --> $DIR/rustc_confusables.rs:14:7
+   |
+LL |     x.push();
+   |       ^^^^ method not found in `BTreeSet`
+   |
+help: you might have meant to use `insert`
+   |
+LL |     x.insert();
+   |       ~~~~~~
+
+error[E0599]: no method named `test` found for struct `rustc_confusables_across_crate::BTreeSet` in the current scope
+  --> $DIR/rustc_confusables.rs:16:7
+   |
+LL |     x.test();
+   |       ^^^^ method not found in `BTreeSet`
+
+error[E0599]: no method named `pulled` found for struct `rustc_confusables_across_crate::BTreeSet` in the current scope
+  --> $DIR/rustc_confusables.rs:18:7
+   |
+LL |     x.pulled();
+   |       ^^^^^^ help: there is a method with a similar name: `pull`
+
+error: aborting due to 5 previous errors
+
+For more information about this error, try `rustc --explain E0599`.