Rollup merge of #147171 - Qelxiros:hashmap_diag, r=fee1-dead

recommend using a HashMap if a HashSet's second generic parameter doesn't implement BuildHasher
closes#147147
~The suggestion span is wrong, but I'm not sure how to find the right one.~ fixed
I'm relatively new to the diagnostics ecosystem, so I'm not sure if `span_help` is the right choice. `span_suggestion_*` might be better, but the output from `x test` looks weird in that case.

Author: matthiaskrgr

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1754,6 +1754,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.note(note);
 }
 
+iflet ty::Adt(adt_def, _) = rcvr_ty.kind(){
+ unsatisfied_predicates.iter().find(|(pred, _parent, _cause)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) =
+ pred.kind().skip_binder()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(
+ err,&pred,*adt_def,
+)
+}else{
+false
+}
+});
+}
+
 *suggested_derive = self.suggest_derive(err, unsatisfied_predicates);
 *unsatisfied_bounds = true;
 }
@@ -2990,7 +3004,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 .filter_map(|e| match e.obligation.predicate.kind().skip_binder(){
  ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
 match pred.self_ty().kind(){
- ty::Adt(_, _) => Some(pred),
+ ty::Adt(_, _) => Some((e.root_obligation.predicate,pred)),
  _ => None,
 }
 }
@@ -3000,18 +3014,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 // Note for local items and foreign items respectively.
 let(mut local_preds,mut foreign_preds):(Vec<_>,Vec<_>) =
- preds.iter().partition(|&pred| {
+ preds.iter().partition(|&(_,pred)| {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  def.did().is_local()
 }else{
 false
 }
 });
 
- local_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ local_preds.sort_by_key(|(_, pred)| pred.trait_ref.to_string());
 let local_def_ids = local_preds
 .iter()
-.filter_map(|pred| match pred.self_ty().kind(){
+.filter_map(|(_,pred)| match pred.self_ty().kind(){
  ty::Adt(def, _) => Some(def.did()),
  _ => None,
 })
@@ -3024,7 +3038,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 })
 .collect::<Vec<_>>()
 .into();
-for pred in&local_preds {
+for(_,pred)in&local_preds {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  local_spans.push_span_label(
 self.tcx.def_span(def.did()),
@@ -3033,7 +3047,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 }
 }
 if local_spans.primary_span().is_some(){
-let msg = iflet[local_pred] = local_preds.as_slice(){
+let msg = iflet[(_,local_pred)] = local_preds.as_slice(){
 format!(
 "an implementation of `{}` might be missing for `{}`",
  local_pred.trait_ref.print_trait_sugared(),
@@ -3051,9 +3065,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.span_note(local_spans, msg);
 }
 
- foreign_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ foreign_preds
+.sort_by_key(|(_, pred):&(_, ty::TraitPredicate<'_>)| pred.trait_ref.to_string());
 
-for pred in foreign_preds {
+for(_,pred)in&foreign_preds {
 let ty = pred.self_ty();
 let ty::Adt(def, _) = ty.kind()else{continue};
 let span = self.tcx.def_span(def.did());
@@ -3066,6 +3081,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  mspan,
 format!("`{ty}` does not implement `{}`", pred.trait_ref.print_trait_sugared()),
 );
+
+ foreign_preds.iter().find(|&(root_pred, pred)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(root_pred)) =
+ root_pred.kind().skip_binder()
+ && letSome(root_adt) = root_pred.self_ty().ty_adt_def()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(err, pred, root_adt)
+}else{
+false
+}
+});
 }
 
 let preds:Vec<_> = errors
@@ -4388,6 +4414,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 self.autoderef(span, rcvr_ty).silence_errors().any(|(ty, _)| is_local(ty))
 }
+
+fnsuggest_hashmap_on_unsatisfied_hashset_buildhasher(
+&self,
+err:&mutDiag<'_>,
+pred:&ty::TraitPredicate<'_>,
+adt: ty::AdtDef<'_>,
+) -> bool{
+ifself.tcx.is_diagnostic_item(sym::HashSet, adt.did())
+ && self.tcx.is_diagnostic_item(sym::BuildHasher, pred.def_id())
+{
+ err.help("you might have intended to use a HashMap instead");
+true
+}else{
+false
+}
+}
 }
 
 #[derive(Copy,Clone,Debug)]

compiler/rustc_span/src/symbol.rs

@@ -191,6 +191,7 @@ symbols! {
 Borrow,
 BorrowMut,
 Break,
+BuildHasher,
 C,
 CStr,
 C_dash_unwind:"C-unwind",

library/core/src/hash/mod.rs

@@ -633,6 +633,7 @@ impl<H: Hasher + ?Sized> Hasher for &mut H {
 ///
 /// [`build_hasher`]: BuildHasher::build_hasher
 /// [`HashMap`]: ../../std/collections/struct.HashMap.html
+#[cfg_attr(not(test), rustc_diagnostic_item = "BuildHasher")]
 #[stable(since = "1.7.0", feature = "build_hasher")]
 pubtraitBuildHasher{
 /// Type of the hasher that will be created.

tests/ui/hashmap/hashset_generics.rs

@@ -0,0 +1,20 @@
+use std::collections::HashSet;
+
+#[derive(PartialEq)]
+//~^ NOTE in this expansion of
+//~| NOTE in this expansion of
+//~| NOTE in this expansion of
+pubstructMyStruct{
+pubparameters:HashSet<String,String>,
+//~^ NOTE `String` does not implement `BuildHasher`
+//~| ERROR binary operation
+//~| HELP use a HashMap
+}
+
+fnmain(){
+let h1 = HashSet::<usize,usize>::with_hasher(0);
+ h1.insert(1);
+//~^ ERROR its trait bounds were not satisfied
+//~| NOTE the following trait bounds
+//~| HELP use a HashMap
+}

tests/ui/hashmap/hashset_generics.stderr

@@ -0,0 +1,29 @@
+error[E0369]: binary operation `==` cannot be applied to type `HashSet<String, String>`
+ --> $DIR/hashset_generics.rs:8:5
+ |
+LL | #[derive(PartialEq)]
+ | --------- in this derive macro expansion
+...
+LL | pub parameters: HashSet<String, String>,
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+note: `String` does not implement `BuildHasher`
+ --> $SRC_DIR/alloc/src/string.rs:LL:COL
+ |
+ = note: `String` is defined in another crate
+ = help: you might have intended to use a HashMap instead
+
+error[E0599]: the method `insert` exists for struct `HashSet<usize, usize>`, but its trait bounds were not satisfied
+ --> $DIR/hashset_generics.rs:16:8
+ |
+LL | h1.insert(1);
+ | ^^^^^^
+ |
+ = note: the following trait bounds were not satisfied:
+ `usize: BuildHasher`
+ = help: you might have intended to use a HashMap instead
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0369, E0599.
+For more information about an error, try `rustc --explain E0369`.

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1754,6 +1754,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.note(note);
 }
 
+iflet ty::Adt(adt_def, _) = rcvr_ty.kind(){
+ unsatisfied_predicates.iter().find(|(pred, _parent, _cause)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) =
+ pred.kind().skip_binder()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(
+ err,&pred,*adt_def,
+)
+}else{
+false
+}
+});
+}
+
 *suggested_derive = self.suggest_derive(err, unsatisfied_predicates);
 *unsatisfied_bounds = true;
 }
@@ -2990,7 +3004,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 .filter_map(|e| match e.obligation.predicate.kind().skip_binder(){
  ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
 match pred.self_ty().kind(){
- ty::Adt(_, _) => Some(pred),
+ ty::Adt(_, _) => Some((e.root_obligation.predicate,pred)),
  _ => None,
 }
 }
@@ -3000,18 +3014,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 // Note for local items and foreign items respectively.
 let(mut local_preds,mut foreign_preds):(Vec<_>,Vec<_>) =
- preds.iter().partition(|&pred| {
+ preds.iter().partition(|&(_,pred)| {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  def.did().is_local()
 }else{
 false
 }
 });
 
- local_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ local_preds.sort_by_key(|(_, pred)| pred.trait_ref.to_string());
 let local_def_ids = local_preds
 .iter()
-.filter_map(|pred| match pred.self_ty().kind(){
+.filter_map(|(_,pred)| match pred.self_ty().kind(){
  ty::Adt(def, _) => Some(def.did()),
  _ => None,
 })
@@ -3024,7 +3038,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 })
 .collect::<Vec<_>>()
 .into();
-for pred in&local_preds {
+for(_,pred)in&local_preds {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  local_spans.push_span_label(
 self.tcx.def_span(def.did()),
@@ -3033,7 +3047,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 }
 }
 if local_spans.primary_span().is_some(){
-let msg = iflet[local_pred] = local_preds.as_slice(){
+let msg = iflet[(_,local_pred)] = local_preds.as_slice(){
 format!(
 "an implementation of `{}` might be missing for `{}`",
  local_pred.trait_ref.print_trait_sugared(),
@@ -3051,9 +3065,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.span_note(local_spans, msg);
 }
 
- foreign_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ foreign_preds
+.sort_by_key(|(_, pred):&(_, ty::TraitPredicate<'_>)| pred.trait_ref.to_string());
 
-for pred in foreign_preds {
+for(_,pred)in&foreign_preds {
 let ty = pred.self_ty();
 let ty::Adt(def, _) = ty.kind()else{continue};
 let span = self.tcx.def_span(def.did());
@@ -3066,6 +3081,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  mspan,
 format!("`{ty}` does not implement `{}`", pred.trait_ref.print_trait_sugared()),
 );
+
+ foreign_preds.iter().find(|&(root_pred, pred)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(root_pred)) =
+ root_pred.kind().skip_binder()
+ && letSome(root_adt) = root_pred.self_ty().ty_adt_def()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(err, pred, root_adt)
+}else{
+false
+}
+});
 }
 
 let preds:Vec<_> = errors
@@ -4388,6 +4414,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 self.autoderef(span, rcvr_ty).silence_errors().any(|(ty, _)| is_local(ty))
 }
+
+fnsuggest_hashmap_on_unsatisfied_hashset_buildhasher(
+&self,
+err:&mutDiag<'_>,
+pred:&ty::TraitPredicate<'_>,
+adt: ty::AdtDef<'_>,
+) -> bool{
+ifself.tcx.is_diagnostic_item(sym::HashSet, adt.did())
+ && self.tcx.is_diagnostic_item(sym::BuildHasher, pred.def_id())
+{
+ err.help("you might have intended to use a HashMap instead");
+true
+}else{
+false
+}
+}
 }
 
 #[derive(Copy,Clone,Debug)]

compiler/rustc_span/src/symbol.rs

@@ -191,6 +191,7 @@ symbols! {
 Borrow,
 BorrowMut,
 Break,
+BuildHasher,
 C,
 CStr,
 C_dash_unwind:"C-unwind",

library/core/src/hash/mod.rs

@@ -633,6 +633,7 @@ impl<H: Hasher + ?Sized> Hasher for &mut H {
 ///
 /// [`build_hasher`]: BuildHasher::build_hasher
 /// [`HashMap`]: ../../std/collections/struct.HashMap.html
+#[cfg_attr(not(test), rustc_diagnostic_item = "BuildHasher")]
 #[stable(since = "1.7.0", feature = "build_hasher")]
 pubtraitBuildHasher{
 /// Type of the hasher that will be created.

tests/ui/hashmap/hashset_generics.rs

@@ -0,0 +1,20 @@
+use std::collections::HashSet;
+
+#[derive(PartialEq)]
+//~^ NOTE in this expansion of
+//~| NOTE in this expansion of
+//~| NOTE in this expansion of
+pubstructMyStruct{
+pubparameters:HashSet<String,String>,
+//~^ NOTE `String` does not implement `BuildHasher`
+//~| ERROR binary operation
+//~| HELP use a HashMap
+}
+
+fnmain(){
+let h1 = HashSet::<usize,usize>::with_hasher(0);
+ h1.insert(1);
+//~^ ERROR its trait bounds were not satisfied
+//~| NOTE the following trait bounds
+//~| HELP use a HashMap
+}

tests/ui/hashmap/hashset_generics.stderr

@@ -0,0 +1,29 @@
+error[E0369]: binary operation `==` cannot be applied to type `HashSet<String, String>`
+ --> $DIR/hashset_generics.rs:8:5
+ |
+LL | #[derive(PartialEq)]
+ | --------- in this derive macro expansion
+...
+LL | pub parameters: HashSet<String, String>,
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+note: `String` does not implement `BuildHasher`
+ --> $SRC_DIR/alloc/src/string.rs:LL:COL
+ |
+ = note: `String` is defined in another crate
+ = help: you might have intended to use a HashMap instead
+
+error[E0599]: the method `insert` exists for struct `HashSet<usize, usize>`, but its trait bounds were not satisfied
+ --> $DIR/hashset_generics.rs:16:8
+ |
+LL | h1.insert(1);
+ | ^^^^^^
+ |
+ = note: the following trait bounds were not satisfied:
+ `usize: BuildHasher`
+ = help: you might have intended to use a HashMap instead
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0369, E0599.
+For more information about an error, try `rustc --explain E0369`.

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1754,6 +1754,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.note(note);
 }
 
+iflet ty::Adt(adt_def, _) = rcvr_ty.kind(){
+ unsatisfied_predicates.iter().find(|(pred, _parent, _cause)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) =
+ pred.kind().skip_binder()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(
+ err,&pred,*adt_def,
+)
+}else{
+false
+}
+});
+}
+
 *suggested_derive = self.suggest_derive(err, unsatisfied_predicates);
 *unsatisfied_bounds = true;
 }
@@ -2990,7 +3004,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 .filter_map(|e| match e.obligation.predicate.kind().skip_binder(){
  ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
 match pred.self_ty().kind(){
- ty::Adt(_, _) => Some(pred),
+ ty::Adt(_, _) => Some((e.root_obligation.predicate,pred)),
  _ => None,
 }
 }
@@ -3000,18 +3014,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 // Note for local items and foreign items respectively.
 let(mut local_preds,mut foreign_preds):(Vec<_>,Vec<_>) =
- preds.iter().partition(|&pred| {
+ preds.iter().partition(|&(_,pred)| {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  def.did().is_local()
 }else{
 false
 }
 });
 
- local_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ local_preds.sort_by_key(|(_, pred)| pred.trait_ref.to_string());
 let local_def_ids = local_preds
 .iter()
-.filter_map(|pred| match pred.self_ty().kind(){
+.filter_map(|(_,pred)| match pred.self_ty().kind(){
  ty::Adt(def, _) => Some(def.did()),
  _ => None,
 })
@@ -3024,7 +3038,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 })
 .collect::<Vec<_>>()
 .into();
-for pred in&local_preds {
+for(_,pred)in&local_preds {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  local_spans.push_span_label(
 self.tcx.def_span(def.did()),
@@ -3033,7 +3047,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 }
 }
 if local_spans.primary_span().is_some(){
-let msg = iflet[local_pred] = local_preds.as_slice(){
+let msg = iflet[(_,local_pred)] = local_preds.as_slice(){
 format!(
 "an implementation of `{}` might be missing for `{}`",
  local_pred.trait_ref.print_trait_sugared(),
@@ -3051,9 +3065,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.span_note(local_spans, msg);
 }
 
- foreign_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ foreign_preds
+.sort_by_key(|(_, pred):&(_, ty::TraitPredicate<'_>)| pred.trait_ref.to_string());
 
-for pred in foreign_preds {
+for(_,pred)in&foreign_preds {
 let ty = pred.self_ty();
 let ty::Adt(def, _) = ty.kind()else{continue};
 let span = self.tcx.def_span(def.did());
@@ -3066,6 +3081,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  mspan,
 format!("`{ty}` does not implement `{}`", pred.trait_ref.print_trait_sugared()),
 );
+
+ foreign_preds.iter().find(|&(root_pred, pred)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(root_pred)) =
+ root_pred.kind().skip_binder()
+ && letSome(root_adt) = root_pred.self_ty().ty_adt_def()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(err, pred, root_adt)
+}else{
+false
+}
+});
 }
 
 let preds:Vec<_> = errors
@@ -4388,6 +4414,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 self.autoderef(span, rcvr_ty).silence_errors().any(|(ty, _)| is_local(ty))
 }
+
+fnsuggest_hashmap_on_unsatisfied_hashset_buildhasher(
+&self,
+err:&mutDiag<'_>,
+pred:&ty::TraitPredicate<'_>,
+adt: ty::AdtDef<'_>,
+) -> bool{
+ifself.tcx.is_diagnostic_item(sym::HashSet, adt.did())
+ && self.tcx.is_diagnostic_item(sym::BuildHasher, pred.def_id())
+{
+ err.help("you might have intended to use a HashMap instead");
+true
+}else{
+false
+}
+}
 }
 
 #[derive(Copy,Clone,Debug)]

compiler/rustc_span/src/symbol.rs

@@ -191,6 +191,7 @@ symbols! {
 Borrow,
 BorrowMut,
 Break,
+BuildHasher,
 C,
 CStr,
 C_dash_unwind:"C-unwind",

library/core/src/hash/mod.rs

@@ -633,6 +633,7 @@ impl<H: Hasher + ?Sized> Hasher for &mut H {
 ///
 /// [`build_hasher`]: BuildHasher::build_hasher
 /// [`HashMap`]: ../../std/collections/struct.HashMap.html
+#[cfg_attr(not(test), rustc_diagnostic_item = "BuildHasher")]
 #[stable(since = "1.7.0", feature = "build_hasher")]
 pubtraitBuildHasher{
 /// Type of the hasher that will be created.

tests/ui/hashmap/hashset_generics.rs

@@ -0,0 +1,20 @@
+use std::collections::HashSet;
+
+#[derive(PartialEq)]
+//~^ NOTE in this expansion of
+//~| NOTE in this expansion of
+//~| NOTE in this expansion of
+pubstructMyStruct{
+pubparameters:HashSet<String,String>,
+//~^ NOTE `String` does not implement `BuildHasher`
+//~| ERROR binary operation
+//~| HELP use a HashMap
+}
+
+fnmain(){
+let h1 = HashSet::<usize,usize>::with_hasher(0);
+ h1.insert(1);
+//~^ ERROR its trait bounds were not satisfied
+//~| NOTE the following trait bounds
+//~| HELP use a HashMap
+}

tests/ui/hashmap/hashset_generics.stderr

@@ -0,0 +1,29 @@
+error[E0369]: binary operation `==` cannot be applied to type `HashSet<String, String>`
+ --> $DIR/hashset_generics.rs:8:5
+ |
+LL | #[derive(PartialEq)]
+ | --------- in this derive macro expansion
+...
+LL | pub parameters: HashSet<String, String>,
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+note: `String` does not implement `BuildHasher`
+ --> $SRC_DIR/alloc/src/string.rs:LL:COL
+ |
+ = note: `String` is defined in another crate
+ = help: you might have intended to use a HashMap instead
+
+error[E0599]: the method `insert` exists for struct `HashSet<usize, usize>`, but its trait bounds were not satisfied
+ --> $DIR/hashset_generics.rs:16:8
+ |
+LL | h1.insert(1);
+ | ^^^^^^
+ |
+ = note: the following trait bounds were not satisfied:
+ `usize: BuildHasher`
+ = help: you might have intended to use a HashMap instead
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0369, E0599.
+For more information about an error, try `rustc --explain E0369`.

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1754,6 +1754,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.note(note);
 }
 
+iflet ty::Adt(adt_def, _) = rcvr_ty.kind(){
+ unsatisfied_predicates.iter().find(|(pred, _parent, _cause)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) =
+ pred.kind().skip_binder()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(
+ err,&pred,*adt_def,
+)
+}else{
+false
+}
+});
+}
+
 *suggested_derive = self.suggest_derive(err, unsatisfied_predicates);
 *unsatisfied_bounds = true;
 }
@@ -2990,7 +3004,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 .filter_map(|e| match e.obligation.predicate.kind().skip_binder(){
  ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
 match pred.self_ty().kind(){
- ty::Adt(_, _) => Some(pred),
+ ty::Adt(_, _) => Some((e.root_obligation.predicate,pred)),
  _ => None,
 }
 }
@@ -3000,18 +3014,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 // Note for local items and foreign items respectively.
 let(mut local_preds,mut foreign_preds):(Vec<_>,Vec<_>) =
- preds.iter().partition(|&pred| {
+ preds.iter().partition(|&(_,pred)| {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  def.did().is_local()
 }else{
 false
 }
 });
 
- local_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ local_preds.sort_by_key(|(_, pred)| pred.trait_ref.to_string());
 let local_def_ids = local_preds
 .iter()
-.filter_map(|pred| match pred.self_ty().kind(){
+.filter_map(|(_,pred)| match pred.self_ty().kind(){
  ty::Adt(def, _) => Some(def.did()),
  _ => None,
 })
@@ -3024,7 +3038,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 })
 .collect::<Vec<_>>()
 .into();
-for pred in&local_preds {
+for(_,pred)in&local_preds {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  local_spans.push_span_label(
 self.tcx.def_span(def.did()),
@@ -3033,7 +3047,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 }
 }
 if local_spans.primary_span().is_some(){
-let msg = iflet[local_pred] = local_preds.as_slice(){
+let msg = iflet[(_,local_pred)] = local_preds.as_slice(){
 format!(
 "an implementation of `{}` might be missing for `{}`",
  local_pred.trait_ref.print_trait_sugared(),
@@ -3051,9 +3065,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.span_note(local_spans, msg);
 }
 
- foreign_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ foreign_preds
+.sort_by_key(|(_, pred):&(_, ty::TraitPredicate<'_>)| pred.trait_ref.to_string());
 
-for pred in foreign_preds {
+for(_,pred)in&foreign_preds {
 let ty = pred.self_ty();
 let ty::Adt(def, _) = ty.kind()else{continue};
 let span = self.tcx.def_span(def.did());
@@ -3066,6 +3081,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  mspan,
 format!("`{ty}` does not implement `{}`", pred.trait_ref.print_trait_sugared()),
 );
+
+ foreign_preds.iter().find(|&(root_pred, pred)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(root_pred)) =
+ root_pred.kind().skip_binder()
+ && letSome(root_adt) = root_pred.self_ty().ty_adt_def()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(err, pred, root_adt)
+}else{
+false
+}
+});
 }
 
 let preds:Vec<_> = errors
@@ -4388,6 +4414,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 self.autoderef(span, rcvr_ty).silence_errors().any(|(ty, _)| is_local(ty))
 }
+
+fnsuggest_hashmap_on_unsatisfied_hashset_buildhasher(
+&self,
+err:&mutDiag<'_>,
+pred:&ty::TraitPredicate<'_>,
+adt: ty::AdtDef<'_>,
+) -> bool{
+ifself.tcx.is_diagnostic_item(sym::HashSet, adt.did())
+ && self.tcx.is_diagnostic_item(sym::BuildHasher, pred.def_id())
+{
+ err.help("you might have intended to use a HashMap instead");
+true
+}else{
+false
+}
+}
 }
 
 #[derive(Copy,Clone,Debug)]

compiler/rustc_span/src/symbol.rs

@@ -191,6 +191,7 @@ symbols! {
 Borrow,
 BorrowMut,
 Break,
+BuildHasher,
 C,
 CStr,
 C_dash_unwind:"C-unwind",

library/core/src/hash/mod.rs

@@ -633,6 +633,7 @@ impl<H: Hasher + ?Sized> Hasher for &mut H {
 ///
 /// [`build_hasher`]: BuildHasher::build_hasher
 /// [`HashMap`]: ../../std/collections/struct.HashMap.html
+#[cfg_attr(not(test), rustc_diagnostic_item = "BuildHasher")]
 #[stable(since = "1.7.0", feature = "build_hasher")]
 pubtraitBuildHasher{
 /// Type of the hasher that will be created.

tests/ui/hashmap/hashset_generics.rs

@@ -0,0 +1,20 @@
+use std::collections::HashSet;
+
+#[derive(PartialEq)]
+//~^ NOTE in this expansion of
+//~| NOTE in this expansion of
+//~| NOTE in this expansion of
+pubstructMyStruct{
+pubparameters:HashSet<String,String>,
+//~^ NOTE `String` does not implement `BuildHasher`
+//~| ERROR binary operation
+//~| HELP use a HashMap
+}
+
+fnmain(){
+let h1 = HashSet::<usize,usize>::with_hasher(0);
+ h1.insert(1);
+//~^ ERROR its trait bounds were not satisfied
+//~| NOTE the following trait bounds
+//~| HELP use a HashMap
+}

tests/ui/hashmap/hashset_generics.stderr

@@ -0,0 +1,29 @@
+error[E0369]: binary operation `==` cannot be applied to type `HashSet<String, String>`
+ --> $DIR/hashset_generics.rs:8:5
+ |
+LL | #[derive(PartialEq)]
+ | --------- in this derive macro expansion
+...
+LL | pub parameters: HashSet<String, String>,
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+note: `String` does not implement `BuildHasher`
+ --> $SRC_DIR/alloc/src/string.rs:LL:COL
+ |
+ = note: `String` is defined in another crate
+ = help: you might have intended to use a HashMap instead
+
+error[E0599]: the method `insert` exists for struct `HashSet<usize, usize>`, but its trait bounds were not satisfied
+ --> $DIR/hashset_generics.rs:16:8
+ |
+LL | h1.insert(1);
+ | ^^^^^^
+ |
+ = note: the following trait bounds were not satisfied:
+ `usize: BuildHasher`
+ = help: you might have intended to use a HashMap instead
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0369, E0599.
+For more information about an error, try `rustc --explain E0369`.

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1754,6 +1754,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.note(note);
 }
 
+iflet ty::Adt(adt_def, _) = rcvr_ty.kind(){
+ unsatisfied_predicates.iter().find(|(pred, _parent, _cause)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) =
+ pred.kind().skip_binder()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(
+ err,&pred,*adt_def,
+)
+}else{
+false
+}
+});
+}
+
 *suggested_derive = self.suggest_derive(err, unsatisfied_predicates);
 *unsatisfied_bounds = true;
 }
@@ -2990,7 +3004,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 .filter_map(|e| match e.obligation.predicate.kind().skip_binder(){
  ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
 match pred.self_ty().kind(){
- ty::Adt(_, _) => Some(pred),
+ ty::Adt(_, _) => Some((e.root_obligation.predicate,pred)),
  _ => None,
 }
 }
@@ -3000,18 +3014,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 // Note for local items and foreign items respectively.
 let(mut local_preds,mut foreign_preds):(Vec<_>,Vec<_>) =
- preds.iter().partition(|&pred| {
+ preds.iter().partition(|&(_,pred)| {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  def.did().is_local()
 }else{
 false
 }
 });
 
- local_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ local_preds.sort_by_key(|(_, pred)| pred.trait_ref.to_string());
 let local_def_ids = local_preds
 .iter()
-.filter_map(|pred| match pred.self_ty().kind(){
+.filter_map(|(_,pred)| match pred.self_ty().kind(){
  ty::Adt(def, _) => Some(def.did()),
  _ => None,
 })
@@ -3024,7 +3038,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 })
 .collect::<Vec<_>>()
 .into();
-for pred in&local_preds {
+for(_,pred)in&local_preds {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  local_spans.push_span_label(
 self.tcx.def_span(def.did()),
@@ -3033,7 +3047,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 }
 }
 if local_spans.primary_span().is_some(){
-let msg = iflet[local_pred] = local_preds.as_slice(){
+let msg = iflet[(_,local_pred)] = local_preds.as_slice(){
 format!(
 "an implementation of `{}` might be missing for `{}`",
  local_pred.trait_ref.print_trait_sugared(),
@@ -3051,9 +3065,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.span_note(local_spans, msg);
 }
 
- foreign_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ foreign_preds
+.sort_by_key(|(_, pred):&(_, ty::TraitPredicate<'_>)| pred.trait_ref.to_string());
 
-for pred in foreign_preds {
+for(_,pred)in&foreign_preds {
 let ty = pred.self_ty();
 let ty::Adt(def, _) = ty.kind()else{continue};
 let span = self.tcx.def_span(def.did());
@@ -3066,6 +3081,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  mspan,
 format!("`{ty}` does not implement `{}`", pred.trait_ref.print_trait_sugared()),
 );
+
+ foreign_preds.iter().find(|&(root_pred, pred)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(root_pred)) =
+ root_pred.kind().skip_binder()
+ && letSome(root_adt) = root_pred.self_ty().ty_adt_def()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(err, pred, root_adt)
+}else{
+false
+}
+});
 }
 
 let preds:Vec<_> = errors
@@ -4388,6 +4414,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 self.autoderef(span, rcvr_ty).silence_errors().any(|(ty, _)| is_local(ty))
 }
+
+fnsuggest_hashmap_on_unsatisfied_hashset_buildhasher(
+&self,
+err:&mutDiag<'_>,
+pred:&ty::TraitPredicate<'_>,
+adt: ty::AdtDef<'_>,
+) -> bool{
+ifself.tcx.is_diagnostic_item(sym::HashSet, adt.did())
+ && self.tcx.is_diagnostic_item(sym::BuildHasher, pred.def_id())
+{
+ err.help("you might have intended to use a HashMap instead");
+true
+}else{
+false
+}
+}
 }
 
 #[derive(Copy,Clone,Debug)]

compiler/rustc_span/src/symbol.rs

@@ -191,6 +191,7 @@ symbols! {
 Borrow,
 BorrowMut,
 Break,
+BuildHasher,
 C,
 CStr,
 C_dash_unwind:"C-unwind",

library/core/src/hash/mod.rs

@@ -633,6 +633,7 @@ impl<H: Hasher + ?Sized> Hasher for &mut H {
 ///
 /// [`build_hasher`]: BuildHasher::build_hasher
 /// [`HashMap`]: ../../std/collections/struct.HashMap.html
+#[cfg_attr(not(test), rustc_diagnostic_item = "BuildHasher")]
 #[stable(since = "1.7.0", feature = "build_hasher")]
 pubtraitBuildHasher{
 /// Type of the hasher that will be created.

tests/ui/hashmap/hashset_generics.rs

@@ -0,0 +1,20 @@
+use std::collections::HashSet;
+
+#[derive(PartialEq)]
+//~^ NOTE in this expansion of
+//~| NOTE in this expansion of
+//~| NOTE in this expansion of
+pubstructMyStruct{
+pubparameters:HashSet<String,String>,
+//~^ NOTE `String` does not implement `BuildHasher`
+//~| ERROR binary operation
+//~| HELP use a HashMap
+}
+
+fnmain(){
+let h1 = HashSet::<usize,usize>::with_hasher(0);
+ h1.insert(1);
+//~^ ERROR its trait bounds were not satisfied
+//~| NOTE the following trait bounds
+//~| HELP use a HashMap
+}

tests/ui/hashmap/hashset_generics.stderr

@@ -0,0 +1,29 @@
+error[E0369]: binary operation `==` cannot be applied to type `HashSet<String, String>`
+ --> $DIR/hashset_generics.rs:8:5
+ |
+LL | #[derive(PartialEq)]
+ | --------- in this derive macro expansion
+...
+LL | pub parameters: HashSet<String, String>,
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+note: `String` does not implement `BuildHasher`
+ --> $SRC_DIR/alloc/src/string.rs:LL:COL
+ |
+ = note: `String` is defined in another crate
+ = help: you might have intended to use a HashMap instead
+
+error[E0599]: the method `insert` exists for struct `HashSet<usize, usize>`, but its trait bounds were not satisfied
+ --> $DIR/hashset_generics.rs:16:8
+ |
+LL | h1.insert(1);
+ | ^^^^^^
+ |
+ = note: the following trait bounds were not satisfied:
+ `usize: BuildHasher`
+ = help: you might have intended to use a HashMap instead
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0369, E0599.
+For more information about an error, try `rustc --explain E0369`.

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1754,6 +1754,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.note(note);
 }
 
+iflet ty::Adt(adt_def, _) = rcvr_ty.kind(){
+ unsatisfied_predicates.iter().find(|(pred, _parent, _cause)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) =
+ pred.kind().skip_binder()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(
+ err,&pred,*adt_def,
+)
+}else{
+false
+}
+});
+}
+
 *suggested_derive = self.suggest_derive(err, unsatisfied_predicates);
 *unsatisfied_bounds = true;
 }
@@ -2990,7 +3004,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 .filter_map(|e| match e.obligation.predicate.kind().skip_binder(){
  ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
 match pred.self_ty().kind(){
- ty::Adt(_, _) => Some(pred),
+ ty::Adt(_, _) => Some((e.root_obligation.predicate,pred)),
  _ => None,
 }
 }
@@ -3000,18 +3014,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 // Note for local items and foreign items respectively.
 let(mut local_preds,mut foreign_preds):(Vec<_>,Vec<_>) =
- preds.iter().partition(|&pred| {
+ preds.iter().partition(|&(_,pred)| {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  def.did().is_local()
 }else{
 false
 }
 });
 
- local_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ local_preds.sort_by_key(|(_, pred)| pred.trait_ref.to_string());
 let local_def_ids = local_preds
 .iter()
-.filter_map(|pred| match pred.self_ty().kind(){
+.filter_map(|(_,pred)| match pred.self_ty().kind(){
  ty::Adt(def, _) => Some(def.did()),
  _ => None,
 })
@@ -3024,7 +3038,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 })
 .collect::<Vec<_>>()
 .into();
-for pred in&local_preds {
+for(_,pred)in&local_preds {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  local_spans.push_span_label(
 self.tcx.def_span(def.did()),
@@ -3033,7 +3047,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 }
 }
 if local_spans.primary_span().is_some(){
-let msg = iflet[local_pred] = local_preds.as_slice(){
+let msg = iflet[(_,local_pred)] = local_preds.as_slice(){
 format!(
 "an implementation of `{}` might be missing for `{}`",
  local_pred.trait_ref.print_trait_sugared(),
@@ -3051,9 +3065,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.span_note(local_spans, msg);
 }
 
- foreign_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ foreign_preds
+.sort_by_key(|(_, pred):&(_, ty::TraitPredicate<'_>)| pred.trait_ref.to_string());
 
-for pred in foreign_preds {
+for(_,pred)in&foreign_preds {
 let ty = pred.self_ty();
 let ty::Adt(def, _) = ty.kind()else{continue};
 let span = self.tcx.def_span(def.did());
@@ -3066,6 +3081,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  mspan,
 format!("`{ty}` does not implement `{}`", pred.trait_ref.print_trait_sugared()),
 );
+
+ foreign_preds.iter().find(|&(root_pred, pred)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(root_pred)) =
+ root_pred.kind().skip_binder()
+ && letSome(root_adt) = root_pred.self_ty().ty_adt_def()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(err, pred, root_adt)
+}else{
+false
+}
+});
 }
 
 let preds:Vec<_> = errors
@@ -4388,6 +4414,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 self.autoderef(span, rcvr_ty).silence_errors().any(|(ty, _)| is_local(ty))
 }
+
+fnsuggest_hashmap_on_unsatisfied_hashset_buildhasher(
+&self,
+err:&mutDiag<'_>,
+pred:&ty::TraitPredicate<'_>,
+adt: ty::AdtDef<'_>,
+) -> bool{
+ifself.tcx.is_diagnostic_item(sym::HashSet, adt.did())
+ && self.tcx.is_diagnostic_item(sym::BuildHasher, pred.def_id())
+{
+ err.help("you might have intended to use a HashMap instead");
+true
+}else{
+false
+}
+}
 }
 
 #[derive(Copy,Clone,Debug)]

compiler/rustc_span/src/symbol.rs

@@ -191,6 +191,7 @@ symbols! {
 Borrow,
 BorrowMut,
 Break,
+BuildHasher,
 C,
 CStr,
 C_dash_unwind:"C-unwind",

library/core/src/hash/mod.rs

@@ -633,6 +633,7 @@ impl<H: Hasher + ?Sized> Hasher for &mut H {
 ///
 /// [`build_hasher`]: BuildHasher::build_hasher
 /// [`HashMap`]: ../../std/collections/struct.HashMap.html
+#[cfg_attr(not(test), rustc_diagnostic_item = "BuildHasher")]
 #[stable(since = "1.7.0", feature = "build_hasher")]
 pubtraitBuildHasher{
 /// Type of the hasher that will be created.

tests/ui/hashmap/hashset_generics.rs

@@ -0,0 +1,20 @@
+use std::collections::HashSet;
+
+#[derive(PartialEq)]
+//~^ NOTE in this expansion of
+//~| NOTE in this expansion of
+//~| NOTE in this expansion of
+pubstructMyStruct{
+pubparameters:HashSet<String,String>,
+//~^ NOTE `String` does not implement `BuildHasher`
+//~| ERROR binary operation
+//~| HELP use a HashMap
+}
+
+fnmain(){
+let h1 = HashSet::<usize,usize>::with_hasher(0);
+ h1.insert(1);
+//~^ ERROR its trait bounds were not satisfied
+//~| NOTE the following trait bounds
+//~| HELP use a HashMap
+}

tests/ui/hashmap/hashset_generics.stderr

@@ -0,0 +1,29 @@
+error[E0369]: binary operation `==` cannot be applied to type `HashSet<String, String>`
+ --> $DIR/hashset_generics.rs:8:5
+ |
+LL | #[derive(PartialEq)]
+ | --------- in this derive macro expansion
+...
+LL | pub parameters: HashSet<String, String>,
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+note: `String` does not implement `BuildHasher`
+ --> $SRC_DIR/alloc/src/string.rs:LL:COL
+ |
+ = note: `String` is defined in another crate
+ = help: you might have intended to use a HashMap instead
+
+error[E0599]: the method `insert` exists for struct `HashSet<usize, usize>`, but its trait bounds were not satisfied
+ --> $DIR/hashset_generics.rs:16:8
+ |
+LL | h1.insert(1);
+ | ^^^^^^
+ |
+ = note: the following trait bounds were not satisfied:
+ `usize: BuildHasher`
+ = help: you might have intended to use a HashMap instead
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0369, E0599.
+For more information about an error, try `rustc --explain E0369`.

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1754,6 +1754,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.note(note);
 }
 
+iflet ty::Adt(adt_def, _) = rcvr_ty.kind(){
+ unsatisfied_predicates.iter().find(|(pred, _parent, _cause)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) =
+ pred.kind().skip_binder()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(
+ err,&pred,*adt_def,
+)
+}else{
+false
+}
+});
+}
+
 *suggested_derive = self.suggest_derive(err, unsatisfied_predicates);
 *unsatisfied_bounds = true;
 }
@@ -2990,7 +3004,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 .filter_map(|e| match e.obligation.predicate.kind().skip_binder(){
  ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
 match pred.self_ty().kind(){
- ty::Adt(_, _) => Some(pred),
+ ty::Adt(_, _) => Some((e.root_obligation.predicate,pred)),
  _ => None,
 }
 }
@@ -3000,18 +3014,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 // Note for local items and foreign items respectively.
 let(mut local_preds,mut foreign_preds):(Vec<_>,Vec<_>) =
- preds.iter().partition(|&pred| {
+ preds.iter().partition(|&(_,pred)| {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  def.did().is_local()
 }else{
 false
 }
 });
 
- local_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ local_preds.sort_by_key(|(_, pred)| pred.trait_ref.to_string());
 let local_def_ids = local_preds
 .iter()
-.filter_map(|pred| match pred.self_ty().kind(){
+.filter_map(|(_,pred)| match pred.self_ty().kind(){
  ty::Adt(def, _) => Some(def.did()),
  _ => None,
 })
@@ -3024,7 +3038,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 })
 .collect::<Vec<_>>()
 .into();
-for pred in&local_preds {
+for(_,pred)in&local_preds {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  local_spans.push_span_label(
 self.tcx.def_span(def.did()),
@@ -3033,7 +3047,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 }
 }
 if local_spans.primary_span().is_some(){
-let msg = iflet[local_pred] = local_preds.as_slice(){
+let msg = iflet[(_,local_pred)] = local_preds.as_slice(){
 format!(
 "an implementation of `{}` might be missing for `{}`",
  local_pred.trait_ref.print_trait_sugared(),
@@ -3051,9 +3065,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.span_note(local_spans, msg);
 }
 
- foreign_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ foreign_preds
+.sort_by_key(|(_, pred):&(_, ty::TraitPredicate<'_>)| pred.trait_ref.to_string());
 
-for pred in foreign_preds {
+for(_,pred)in&foreign_preds {
 let ty = pred.self_ty();
 let ty::Adt(def, _) = ty.kind()else{continue};
 let span = self.tcx.def_span(def.did());
@@ -3066,6 +3081,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  mspan,
 format!("`{ty}` does not implement `{}`", pred.trait_ref.print_trait_sugared()),
 );
+
+ foreign_preds.iter().find(|&(root_pred, pred)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(root_pred)) =
+ root_pred.kind().skip_binder()
+ && letSome(root_adt) = root_pred.self_ty().ty_adt_def()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(err, pred, root_adt)
+}else{
+false
+}
+});
 }
 
 let preds:Vec<_> = errors
@@ -4388,6 +4414,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 self.autoderef(span, rcvr_ty).silence_errors().any(|(ty, _)| is_local(ty))
 }
+
+fnsuggest_hashmap_on_unsatisfied_hashset_buildhasher(
+&self,
+err:&mutDiag<'_>,
+pred:&ty::TraitPredicate<'_>,
+adt: ty::AdtDef<'_>,
+) -> bool{
+ifself.tcx.is_diagnostic_item(sym::HashSet, adt.did())
+ && self.tcx.is_diagnostic_item(sym::BuildHasher, pred.def_id())
+{
+ err.help("you might have intended to use a HashMap instead");
+true
+}else{
+false
+}
+}
 }
 
 #[derive(Copy,Clone,Debug)]

compiler/rustc_span/src/symbol.rs

@@ -191,6 +191,7 @@ symbols! {
 Borrow,
 BorrowMut,
 Break,
+BuildHasher,
 C,
 CStr,
 C_dash_unwind:"C-unwind",

library/core/src/hash/mod.rs

@@ -633,6 +633,7 @@ impl<H: Hasher + ?Sized> Hasher for &mut H {
 ///
 /// [`build_hasher`]: BuildHasher::build_hasher
 /// [`HashMap`]: ../../std/collections/struct.HashMap.html
+#[cfg_attr(not(test), rustc_diagnostic_item = "BuildHasher")]
 #[stable(since = "1.7.0", feature = "build_hasher")]
 pubtraitBuildHasher{
 /// Type of the hasher that will be created.

tests/ui/hashmap/hashset_generics.rs

@@ -0,0 +1,20 @@
+use std::collections::HashSet;
+
+#[derive(PartialEq)]
+//~^ NOTE in this expansion of
+//~| NOTE in this expansion of
+//~| NOTE in this expansion of
+pubstructMyStruct{
+pubparameters:HashSet<String,String>,
+//~^ NOTE `String` does not implement `BuildHasher`
+//~| ERROR binary operation
+//~| HELP use a HashMap
+}
+
+fnmain(){
+let h1 = HashSet::<usize,usize>::with_hasher(0);
+ h1.insert(1);
+//~^ ERROR its trait bounds were not satisfied
+//~| NOTE the following trait bounds
+//~| HELP use a HashMap
+}

tests/ui/hashmap/hashset_generics.stderr

@@ -0,0 +1,29 @@
+error[E0369]: binary operation `==` cannot be applied to type `HashSet<String, String>`
+ --> $DIR/hashset_generics.rs:8:5
+ |
+LL | #[derive(PartialEq)]
+ | --------- in this derive macro expansion
+...
+LL | pub parameters: HashSet<String, String>,
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+note: `String` does not implement `BuildHasher`
+ --> $SRC_DIR/alloc/src/string.rs:LL:COL
+ |
+ = note: `String` is defined in another crate
+ = help: you might have intended to use a HashMap instead
+
+error[E0599]: the method `insert` exists for struct `HashSet<usize, usize>`, but its trait bounds were not satisfied
+ --> $DIR/hashset_generics.rs:16:8
+ |
+LL | h1.insert(1);
+ | ^^^^^^
+ |
+ = note: the following trait bounds were not satisfied:
+ `usize: BuildHasher`
+ = help: you might have intended to use a HashMap instead
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0369, E0599.
+For more information about an error, try `rustc --explain E0369`.

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1754,6 +1754,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.note(note);
 }
 
+iflet ty::Adt(adt_def, _) = rcvr_ty.kind(){
+ unsatisfied_predicates.iter().find(|(pred, _parent, _cause)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) =
+ pred.kind().skip_binder()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(
+ err,&pred,*adt_def,
+)
+}else{
+false
+}
+});
+}
+
 *suggested_derive = self.suggest_derive(err, unsatisfied_predicates);
 *unsatisfied_bounds = true;
 }
@@ -2990,7 +3004,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 .filter_map(|e| match e.obligation.predicate.kind().skip_binder(){
  ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
 match pred.self_ty().kind(){
- ty::Adt(_, _) => Some(pred),
+ ty::Adt(_, _) => Some((e.root_obligation.predicate,pred)),
  _ => None,
 }
 }
@@ -3000,18 +3014,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 // Note for local items and foreign items respectively.
 let(mut local_preds,mut foreign_preds):(Vec<_>,Vec<_>) =
- preds.iter().partition(|&pred| {
+ preds.iter().partition(|&(_,pred)| {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  def.did().is_local()
 }else{
 false
 }
 });
 
- local_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ local_preds.sort_by_key(|(_, pred)| pred.trait_ref.to_string());
 let local_def_ids = local_preds
 .iter()
-.filter_map(|pred| match pred.self_ty().kind(){
+.filter_map(|(_,pred)| match pred.self_ty().kind(){
  ty::Adt(def, _) => Some(def.did()),
  _ => None,
 })
@@ -3024,7 +3038,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 })
 .collect::<Vec<_>>()
 .into();
-for pred in&local_preds {
+for(_,pred)in&local_preds {
 iflet ty::Adt(def, _) = pred.self_ty().kind(){
  local_spans.push_span_label(
 self.tcx.def_span(def.did()),
@@ -3033,7 +3047,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 }
 }
 if local_spans.primary_span().is_some(){
-let msg = iflet[local_pred] = local_preds.as_slice(){
+let msg = iflet[(_,local_pred)] = local_preds.as_slice(){
 format!(
 "an implementation of `{}` might be missing for `{}`",
  local_pred.trait_ref.print_trait_sugared(),
@@ -3051,9 +3065,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  err.span_note(local_spans, msg);
 }
 
- foreign_preds.sort_by_key(|pred:&&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
+ foreign_preds
+.sort_by_key(|(_, pred):&(_, ty::TraitPredicate<'_>)| pred.trait_ref.to_string());
 
-for pred in foreign_preds {
+for(_,pred)in&foreign_preds {
 let ty = pred.self_ty();
 let ty::Adt(def, _) = ty.kind()else{continue};
 let span = self.tcx.def_span(def.did());
@@ -3066,6 +3081,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  mspan,
 format!("`{ty}` does not implement `{}`", pred.trait_ref.print_trait_sugared()),
 );
+
+ foreign_preds.iter().find(|&(root_pred, pred)| {
+iflet ty::PredicateKind::Clause(ty::ClauseKind::Trait(root_pred)) =
+ root_pred.kind().skip_binder()
+ && letSome(root_adt) = root_pred.self_ty().ty_adt_def()
+{
+self.suggest_hashmap_on_unsatisfied_hashset_buildhasher(err, pred, root_adt)
+}else{
+false
+}
+});
 }
 
 let preds:Vec<_> = errors
@@ -4388,6 +4414,22 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
 self.autoderef(span, rcvr_ty).silence_errors().any(|(ty, _)| is_local(ty))
 }
+
+fnsuggest_hashmap_on_unsatisfied_hashset_buildhasher(
+&self,
+err:&mutDiag<'_>,
+pred:&ty::TraitPredicate<'_>,
+adt: ty::AdtDef<'_>,
+) -> bool{
+ifself.tcx.is_diagnostic_item(sym::HashSet, adt.did())
+ && self.tcx.is_diagnostic_item(sym::BuildHasher, pred.def_id())
+{
+ err.help("you might have intended to use a HashMap instead");
+true
+}else{
+false
+}
+}
 }
 
 #[derive(Copy,Clone,Debug)]

compiler/rustc_span/src/symbol.rs

@@ -191,6 +191,7 @@ symbols! {
 Borrow,
 BorrowMut,
 Break,
+BuildHasher,
 C,
 CStr,
 C_dash_unwind:"C-unwind",

library/core/src/hash/mod.rs

@@ -633,6 +633,7 @@ impl<H: Hasher + ?Sized> Hasher for &mut H {
 ///
 /// [`build_hasher`]: BuildHasher::build_hasher
 /// [`HashMap`]: ../../std/collections/struct.HashMap.html
+#[cfg_attr(not(test), rustc_diagnostic_item = "BuildHasher")]
 #[stable(since = "1.7.0", feature = "build_hasher")]
 pubtraitBuildHasher{
 /// Type of the hasher that will be created.

tests/ui/hashmap/hashset_generics.rs

@@ -0,0 +1,20 @@
+use std::collections::HashSet;
+
+#[derive(PartialEq)]
+//~^ NOTE in this expansion of
+//~| NOTE in this expansion of
+//~| NOTE in this expansion of
+pubstructMyStruct{
+pubparameters:HashSet<String,String>,
+//~^ NOTE `String` does not implement `BuildHasher`
+//~| ERROR binary operation
+//~| HELP use a HashMap
+}
+
+fnmain(){
+let h1 = HashSet::<usize,usize>::with_hasher(0);
+ h1.insert(1);
+//~^ ERROR its trait bounds were not satisfied
+//~| NOTE the following trait bounds
+//~| HELP use a HashMap
+}

tests/ui/hashmap/hashset_generics.stderr

@@ -0,0 +1,29 @@
+error[E0369]: binary operation `==` cannot be applied to type `HashSet<String, String>`
+ --> $DIR/hashset_generics.rs:8:5
+ |
+LL | #[derive(PartialEq)]
+ | --------- in this derive macro expansion
+...
+LL | pub parameters: HashSet<String, String>,
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+note: `String` does not implement `BuildHasher`
+ --> $SRC_DIR/alloc/src/string.rs:LL:COL
+ |
+ = note: `String` is defined in another crate
+ = help: you might have intended to use a HashMap instead
+
+error[E0599]: the method `insert` exists for struct `HashSet<usize, usize>`, but its trait bounds were not satisfied
+ --> $DIR/hashset_generics.rs:16:8
+ |
+LL | h1.insert(1);
+ | ^^^^^^
+ |
+ = note: the following trait bounds were not satisfied:
+ `usize: BuildHasher`
+ = help: you might have intended to use a HashMap instead
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0369, E0599.
+For more information about an error, try `rustc --explain E0369`.