Fix a bad binop error when we need a call

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -27,8 +27,8 @@ use rustc_middle::traits::util::supertraits;
 use rustc_middle::ty::fast_reject::DeepRejectCtxt;
 use rustc_middle::ty::fast_reject::{simplify_type, TreatParams};
 use rustc_middle::ty::print::{with_crate_prefix, with_forced_trimmed_paths};
+use rustc_middle::ty::IsSuggestable;
 use rustc_middle::ty::{self, GenericArgKind, Ty, TyCtxt, TypeVisitableExt};
-use rustc_middle::ty::{IsSuggestable, ToPolyTraitRef};
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::Symbol;
 use rustc_span::{edit_distance, source_map, ExpnKind, FileName, MacroKind, Span};
@@ -2068,7 +2068,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let mut derives = Vec::<(String, Span, Symbol)>::new();
         let mut traits = Vec::new();
         for (pred, _, _) in unsatisfied_predicates {
-            let ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)) = pred.kind().skip_binder() else { continue };
+            let Some(ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred))) =
+                pred.kind().no_bound_vars()
+            else {
+                continue
+            };
             let adt = match trait_pred.self_ty().ty_adt_def() {
                 Some(adt) if adt.did().is_local() => adt,
                 _ => continue,
@@ -2085,22 +2089,31 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     | sym::Hash
                     | sym::Debug => true,
                     _ => false,
+                } && match trait_pred.trait_ref.substs.as_slice() {
+                    // Only suggest deriving if lhs == rhs...
+                    [lhs, rhs] => {
+                        if let Some(lhs) = lhs.as_type()
+                            && let Some(rhs) = rhs.as_type()
+                        {
+                            self.can_eq(self.param_env, lhs, rhs)
+                        } else {
+                            false
+                        }
+                    },
+                    // Unary ops can always be derived
+                    [_] => true,
+                    _ => false,
                 };
                 if can_derive {
                     let self_name = trait_pred.self_ty().to_string();
                     let self_span = self.tcx.def_span(adt.did());
-                    if let Some(poly_trait_ref) = pred.to_opt_poly_trait_pred() {
-                        for super_trait in supertraits(self.tcx, poly_trait_ref.to_poly_trait_ref())
+                    for super_trait in
+                        supertraits(self.tcx, ty::Binder::dummy(trait_pred.trait_ref))
+                    {
+                        if let Some(parent_diagnostic_name) =
+                            self.tcx.get_diagnostic_name(super_trait.def_id())
                         {
-                            if let Some(parent_diagnostic_name) =
-                                self.tcx.get_diagnostic_name(super_trait.def_id())
-                            {
-                                derives.push((
-                                    self_name.clone(),
-                                    self_span,
-                                    parent_diagnostic_name,
-                                ));
-                            }
+                            derives.push((self_name.clone(), self_span, parent_diagnostic_name));
                         }
                     }
                     derives.push((self_name, self_span, diagnostic_name));

compiler/rustc_hir_typeck/src/op.rs

@@ -408,7 +408,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     }
                 };
 
-                let is_compatible = |lhs_ty, rhs_ty| {
+                let is_compatible_after_call = |lhs_ty, rhs_ty| {
                     self.lookup_op_method(
                         lhs_ty,
                         Some((rhs_expr, rhs_ty)),
@@ -416,6 +416,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         expected,
                     )
                     .is_ok()
+                        // Suggest calling even if, after calling, the types don't
+                        // implement the operator, since it'll lead to better
+                        // diagnostics later.
+                        || self.can_eq(self.param_env, lhs_ty, rhs_ty)
                 };
 
                 // We should suggest `a + b` => `*a + b` if `a` is copy, and suggest
@@ -436,16 +440,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         suggest_deref_binop(*lhs_deref_ty);
                     }
                 } else if self.suggest_fn_call(&mut err, lhs_expr, lhs_ty, |lhs_ty| {
-                    is_compatible(lhs_ty, rhs_ty)
+                    is_compatible_after_call(lhs_ty, rhs_ty)
                 }) || self.suggest_fn_call(&mut err, rhs_expr, rhs_ty, |rhs_ty| {
-                    is_compatible(lhs_ty, rhs_ty)
+                    is_compatible_after_call(lhs_ty, rhs_ty)
                 }) || self.suggest_two_fn_call(
                     &mut err,
                     rhs_expr,
                     rhs_ty,
                     lhs_expr,
                     lhs_ty,
-                    |lhs_ty, rhs_ty| is_compatible(lhs_ty, rhs_ty),
+                    |lhs_ty, rhs_ty| is_compatible_after_call(lhs_ty, rhs_ty),
                 ) {
                     // Cool
                 }

tests/ui/issues/issue-62375.stderr

@@ -11,11 +11,12 @@ note: an implementation of `PartialEq<fn(()) -> A {A::Value}>` might be missing
    |
 LL | enum A {
    | ^^^^^^ must implement `PartialEq<fn(()) -> A {A::Value}>`
-help: consider annotating `A` with `#[derive(PartialEq)]`
-   |
-LL + #[derive(PartialEq)]
-LL | enum A {
+note: the trait `PartialEq` must be implemented
+  --> $SRC_DIR/core/src/cmp.rs:LL:COL
+help: use parentheses to construct this tuple variant
    |
+LL |     a == A::Value(/* () */);
+   |                  ++++++++++
 
 error: aborting due to previous error