Auto merge of #120730 - estebank:confusable-api, r=oli-obk

Provide suggestions through `rustc_confusables` annotations

Help with common API confusion, like asking for `push` when the data structure really has `append`.

```
error[E0599]: no method named `size` found for struct `Vec<{integer}>` in the current scope
  --> $DIR/rustc_confusables_std_cases.rs:17:7
   |
LL |     x.size();
   |       ^^^^
   |
help: you might have meant to use `len`
   |
LL |     x.len();
   |       ~~~
help: there is a method with a similar name
   |
LL |     x.resize();
   |       ~~~~~~
```

Fix #59450 (we can open subsequent tickets for specific cases).

Fix #108437:

```
error[E0599]: `Option<{integer}>` is not an iterator
   --> f101.rs:3:9
    |
3   |     opt.flat_map(|val| Some(val));
    |         ^^^^^^^^ `Option<{integer}>` is not an iterator
    |
   ::: /home/gh-estebank/rust/library/core/src/option.rs:571:1
    |
571 | pub enum Option<T> {
    | ------------------ doesn't satisfy `Option<{integer}>: Iterator`
    |
    = note: the following trait bounds were not satisfied:
            `Option<{integer}>: Iterator`
            which is required by `&mut Option<{integer}>: Iterator`
help: you might have meant to use `and_then`
    |
3   |     opt.and_then(|val| Some(val));
    |         ~~~~~~~~
```

On type error of method call arguments, look at confusables for suggestion. Fix #87212:

```
error[E0308]: mismatched types
    --> f101.rs:8:18
     |
8    |     stuff.append(Thing);
     |           ------ ^^^^^ expected `&mut Vec<Thing>`, found `Thing`
     |           |
     |           arguments to this method are incorrect
     |
     = note: expected mutable reference `&mut Vec<Thing>`
                           found struct `Thing`
note: method defined here
    --> /home/gh-estebank/rust/library/alloc/src/vec/mod.rs:2025:12
     |
2025 |     pub fn append(&mut self, other: &mut Self) {
     |            ^^^^^^
help: you might have meant to use `push`
     |
8    |     stuff.push(Thing);
     |           ~~~~
```

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -1,7 +1,11 @@
 use crate::coercion::CoerceMany;
 use crate::errors::SuggestPtrNullMut;
 use crate::fn_ctxt::arg_matrix::{ArgMatrix, Compatibility, Error, ExpectedIdx, ProvidedIdx};
+use crate::fn_ctxt::infer::FnCall;
 use crate::gather_locals::Declaration;
+use crate::method::probe::IsSuggestion;
+use crate::method::probe::Mode::MethodCall;
+use crate::method::probe::ProbeScope::TraitsInScope;
 use crate::method::MethodCallee;
 use crate::TupleArgumentsFlag::*;
 use crate::{errors, Expectation::*};
@@ -451,7 +455,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         call_expr: &'tcx hir::Expr<'tcx>,
     ) -> ErrorGuaranteed {
         // Next, let's construct the error
-        let (error_span, full_call_span, call_name, is_method) = match &call_expr.kind {
+        let (error_span, call_ident, full_call_span, call_name, is_method) = match &call_expr.kind {
             hir::ExprKind::Call(
                 hir::Expr { hir_id, span, kind: hir::ExprKind::Path(qpath), .. },
                 _,
@@ -463,20 +467,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         CtorOf::Struct => "struct",
                         CtorOf::Variant => "enum variant",
                     };
-                    (call_span, *span, name, false)
+                    (call_span, None, *span, name, false)
                 } else {
-                    (call_span, *span, "function", false)
+                    (call_span, None, *span, "function", false)
                 }
             }
-            hir::ExprKind::Call(hir::Expr { span, .. }, _) => (call_span, *span, "function", false),
+            hir::ExprKind::Call(hir::Expr { span, .. }, _) => {
+                (call_span, None, *span, "function", false)
+            }
             hir::ExprKind::MethodCall(path_segment, _, _, span) => {
                 let ident_span = path_segment.ident.span;
                 let ident_span = if let Some(args) = path_segment.args {
                     ident_span.with_hi(args.span_ext.hi())
                 } else {
                     ident_span
                 };
-                (*span, ident_span, "method", true)
+                (*span, Some(path_segment.ident), ident_span, "method", true)
             }
             k => span_bug!(call_span, "checking argument types on a non-call: `{:?}`", k),
         };
@@ -530,6 +536,104 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let callee_ty = callee_expr
             .and_then(|callee_expr| self.typeck_results.borrow().expr_ty_adjusted_opt(callee_expr));
 
+        // Obtain another method on `Self` that have similar name.
+        let similar_assoc = |call_name: Ident| -> Option<(ty::AssocItem, ty::FnSig<'_>)> {
+            if let Some(callee_ty) = callee_ty
+                && let Ok(Some(assoc)) = self.probe_op(
+                    call_name.span,
+                    MethodCall,
+                    Some(call_name),
+                    None,
+                    IsSuggestion(true),
+                    callee_ty.peel_refs(),
+                    callee_expr.unwrap().hir_id,
+                    TraitsInScope,
+                    |mut ctxt| ctxt.probe_for_similar_candidate(),
+                )
+                && let ty::AssocKind::Fn = assoc.kind
+                && assoc.fn_has_self_parameter
+            {
+                let args = self.infcx.fresh_args_for_item(call_name.span, assoc.def_id);
+                let fn_sig = tcx.fn_sig(assoc.def_id).instantiate(tcx, args);
+                let fn_sig =
+                    self.instantiate_binder_with_fresh_vars(call_name.span, FnCall, fn_sig);
+                Some((assoc, fn_sig));
+            }
+            None
+        };
+
+        let suggest_confusable = |err: &mut DiagnosticBuilder<'_>| {
+            let Some(call_name) = call_ident else {
+                return;
+            };
+            let Some(callee_ty) = callee_ty else {
+                return;
+            };
+            let input_types: Vec<Ty<'_>> = provided_arg_tys.iter().map(|(ty, _)| *ty).collect();
+            // Check for other methods in the following order
+            //  - methods marked as `rustc_confusables` with the provided arguments
+            //  - methods with the same argument type/count and short levenshtein distance
+            //  - methods marked as `rustc_confusables` (done)
+            //  - methods with short levenshtein distance
+
+            // Look for commonly confusable method names considering arguments.
+            if let Some(_name) = self.confusable_method_name(
+                err,
+                callee_ty.peel_refs(),
+                call_name,
+                Some(input_types.clone()),
+            ) {
+                return;
+            }
+            // Look for method names with short levenshtein distance, considering arguments.
+            if let Some((assoc, fn_sig)) = similar_assoc(call_name)
+                && fn_sig.inputs()[1..]
+                    .iter()
+                    .zip(input_types.iter())
+                    .all(|(expected, found)| self.can_coerce(*expected, *found))
+                && fn_sig.inputs()[1..].len() == input_types.len()
+            {
+                err.span_suggestion_verbose(
+                    call_name.span,
+                    format!("you might have meant to use `{}`", assoc.name),
+                    assoc.name,
+                    Applicability::MaybeIncorrect,
+                );
+                return;
+            }
+            // Look for commonly confusable method names disregarding arguments.
+            if let Some(_name) =
+                self.confusable_method_name(err, callee_ty.peel_refs(), call_name, None)
+            {
+                return;
+            }
+            // Look for similarly named methods with levenshtein distance with the right
+            // number of arguments.
+            if let Some((assoc, fn_sig)) = similar_assoc(call_name)
+                && fn_sig.inputs()[1..].len() == input_types.len()
+            {
+                err.span_note(
+                    tcx.def_span(assoc.def_id),
+                    format!(
+                        "there's is a method with similar name `{}`, but the arguments don't match",
+                        assoc.name,
+                    ),
+                );
+                return;
+            }
+            // Fallthrough: look for similarly named methods with levenshtein distance.
+            if let Some((assoc, _)) = similar_assoc(call_name) {
+                err.span_note(
+                    tcx.def_span(assoc.def_id),
+                    format!(
+                        "there's is a method with similar name `{}`, but their argument count \
+                         doesn't match",
+                        assoc.name,
+                    ),
+                );
+                return;
+            }
+        };
         // A "softer" version of the `demand_compatible`, which checks types without persisting them,
         // and treats error types differently
         // This will allow us to "probe" for other argument orders that would likely have been correct
@@ -694,6 +798,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         Some(mismatch_idx),
                         is_method,
                     );
+                    suggest_confusable(&mut err);
                     return err.emit();
                 }
             }
@@ -718,7 +823,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             if cfg!(debug_assertions) {
                 span_bug!(error_span, "expected errors from argument matrix");
             } else {
-                return tcx.dcx().emit_err(errors::ArgMismatchIndeterminate { span: error_span });
+                let mut err =
+                    tcx.dcx().create_err(errors::ArgMismatchIndeterminate { span: error_span });
+                suggest_confusable(&mut err);
+                return err.emit();
             }
         }
 
@@ -733,7 +841,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let trace =
                 mk_trace(provided_span, formal_and_expected_inputs[*expected_idx], provided_ty);
             if !matches!(trace.cause.as_failure_code(*e), FailureCode::Error0308) {
-                reported = Some(self.err_ctxt().report_and_explain_type_error(trace, *e).emit());
+                let mut err = self.err_ctxt().report_and_explain_type_error(trace, *e);
+                suggest_confusable(&mut err);
+                reported = Some(err.emit());
                 return false;
             }
             true
@@ -802,6 +912,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 Some(expected_idx.as_usize()),
                 is_method,
             );
+            suggest_confusable(&mut err);
             return err.emit();
         }
 
@@ -829,6 +940,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .with_code(err_code.to_owned())
         };
 
+        suggest_confusable(&mut err);
         // As we encounter issues, keep track of what we want to provide for the suggestion
         let mut labels = vec![];
         // If there is a single error, we give a specific suggestion; otherwise, we change to

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -54,7 +54,7 @@ pub use self::PickKind::*;
 #[derive(Clone, Copy, Debug)]
 pub struct IsSuggestion(pub bool);
 
-struct ProbeContext<'a, 'tcx> {
+pub(crate) struct ProbeContext<'a, 'tcx> {
     fcx: &'a FnCtxt<'a, 'tcx>,
     span: Span,
     mode: Mode,
@@ -355,7 +355,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         .unwrap()
     }
 
-    fn probe_op<OP, R>(
+    pub(crate) fn probe_op<OP, R>(
         &'a self,
         span: Span,
         mode: Mode,
@@ -1750,7 +1750,9 @@ 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
     /// edit distance based suggestions, we provide at most one such suggestion.
-    fn probe_for_similar_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
+    pub(crate) fn probe_for_similar_candidate(
+        &mut self,
+    ) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> {
         debug!("probing for method names similar to {:?}", self.method_name);
 
         self.probe(|_| {
@@ -1766,6 +1768,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             );
             pcx.allow_similar_names = true;
             pcx.assemble_inherent_candidates();
+            pcx.assemble_extension_candidates_for_all_traits();
 
             let method_names = pcx.candidate_method_names(|_| true);
             pcx.allow_similar_names = false;
@@ -1775,6 +1778,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     pcx.reset();
                     pcx.method_name = Some(method_name);
                     pcx.assemble_inherent_candidates();
+                    pcx.assemble_extension_candidates_for_all_traits();
                     pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item)
                 })
                 .collect();
@@ -1942,7 +1946,21 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         let hir_id = self.fcx.tcx.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 {
+            if sym::doc == attr.name_or_empty() {
+            } else if sym::rustc_confusables == attr.name_or_empty() {
+                let Some(confusables) = attr.meta_item_list() else {
+                    continue;
+                };
+                // #[rustc_confusables("foo", "bar"))]
+                for n in confusables {
+                    if let Some(lit) = n.lit()
+                        && name.as_str() == lit.symbol.as_str()
+                    {
+                        return true;
+                    }
+                }
+                continue;
+            } else {
                 continue;
             };
             let Some(values) = attr.meta_item_list() else {