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recommend using a HashMap if a HashSet's second generic parameter doesn't implement BuildHasher
1 parent bbcbc78 commit 263ccbb

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5 files changed

+104
-10
lines changed

5 files changed

+104
-10
lines changed

‎compiler/rustc_hir_typeck/src/method/suggest.rs‎

Lines changed: 44 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -1337,6 +1337,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
13371337
but its trait bounds were not satisfied"
13381338
)
13391339
});
1340+
13401341
err.primary_message(primary_message);
13411342
if let Some(label) = label {
13421343
custom_span_label = true;
@@ -1353,6 +1354,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
13531354

13541355
suggested_derive = self.suggest_derive(&mut err, unsatisfied_predicates);
13551356

1357+
if let ty::Adt(adt_def, _) = rcvr_ty.kind()
1358+
&& self.tcx.is_diagnostic_item(sym::HashSet, adt_def.did())
1359+
&& unsatisfied_predicates.iter().any(|(pred, _parent, _cause)| {
1360+
if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) =
1361+
pred.kind().skip_binder()
1362+
{
1363+
self.tcx.is_diagnostic_item(sym::BuildHasher, pred.def_id())
1364+
} else {
1365+
false
1366+
}
1367+
})
1368+
{
1369+
err.span_help(span, "you might have intended to use a HashMap instead");
1370+
}
1371+
13561372
unsatisfied_bounds = true;
13571373
}
13581374
} else if let ty::Adt(def, targs) = rcvr_ty.kind()
@@ -2925,7 +2941,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
29252941
.filter_map(|e| match e.obligation.predicate.kind().skip_binder() {
29262942
ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
29272943
match pred.self_ty().kind() {
2928-
ty::Adt(_, _) => Some(pred),
2944+
ty::Adt(_, _) => Some((
2945+
(e.root_obligation.predicate, e.root_obligation.cause.span),
2946+
pred,
2947+
)),
29292948
_ => None,
29302949
}
29312950
}
@@ -2935,18 +2954,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
29352954

29362955
// Note for local items and foreign items respectively.
29372956
let (mut local_preds, mut foreign_preds): (Vec<_>, Vec<_>) =
2938-
preds.iter().partition(|&pred| {
2957+
preds.iter().partition(|&(_, pred)| {
29392958
if let ty::Adt(def, _) = pred.self_ty().kind() {
29402959
def.did().is_local()
29412960
} else {
29422961
false
29432962
}
29442963
});
29452964

2946-
local_preds.sort_by_key(|pred: &&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
2965+
local_preds.sort_by_key(|(_, pred)| pred.trait_ref.to_string());
29472966
let local_def_ids = local_preds
29482967
.iter()
2949-
.filter_map(|pred| match pred.self_ty().kind() {
2968+
.filter_map(|(_, pred)| match pred.self_ty().kind() {
29502969
ty::Adt(def, _) => Some(def.did()),
29512970
_ => None,
29522971
})
@@ -2959,7 +2978,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
29592978
})
29602979
.collect::<Vec<_>>()
29612980
.into();
2962-
for pred in &local_preds {
2981+
for (_, pred) in &local_preds {
29632982
if let ty::Adt(def, _) = pred.self_ty().kind() {
29642983
local_spans.push_span_label(
29652984
self.tcx.def_span(def.did()),
@@ -2968,7 +2987,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
29682987
}
29692988
}
29702989
if local_spans.primary_span().is_some() {
2971-
let msg = if let [local_pred] = local_preds.as_slice() {
2990+
let msg = if let [(_, local_pred)] = local_preds.as_slice() {
29722991
format!(
29732992
"an implementation of `{}` might be missing for `{}`",
29742993
local_pred.trait_ref.print_trait_sugared(),
@@ -2986,10 +3005,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
29863005
err.span_note(local_spans, msg);
29873006
}
29883007

2989-
foreign_preds.sort_by_key(|pred: &&ty::TraitPredicate<'_>| pred.trait_ref.to_string());
3008+
foreign_preds.sort_by_key(|(_, pred)| pred.trait_ref.to_string());
29903009
let foreign_def_ids = foreign_preds
29913010
.iter()
2992-
.filter_map(|pred| match pred.self_ty().kind() {
3011+
.filter_map(|(_, pred)| match pred.self_ty().kind() {
29933012
ty::Adt(def, _) => Some(def.did()),
29943013
_ => None,
29953014
})
@@ -3002,7 +3021,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
30023021
})
30033022
.collect::<Vec<_>>()
30043023
.into();
3005-
for pred in &foreign_preds {
3024+
for (_, pred) in &foreign_preds {
30063025
if let ty::Adt(def, _) = pred.self_ty().kind() {
30073026
foreign_spans.push_span_label(
30083027
self.tcx.def_span(def.did()),
@@ -3011,7 +3030,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
30113030
}
30123031
}
30133032
if foreign_spans.primary_span().is_some() {
3014-
let msg = if let [foreign_pred] = foreign_preds.as_slice() {
3033+
let msg = if let [(_, foreign_pred)] = foreign_preds.as_slice() {
30153034
format!(
30163035
"the foreign item type `{}` doesn't implement `{}`",
30173036
foreign_pred.self_ty(),
@@ -3027,6 +3046,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
30273046
)
30283047
};
30293048
err.span_note(foreign_spans, msg);
3049+
3050+
if let Some(span) = foreign_preds.iter().find_map(|&((root_pred, span), pred)| {
3051+
match root_pred.kind().skip_binder() {
3052+
ty::PredicateKind::Clause(ty::ClauseKind::Trait(root_pred))
3053+
if let Some(root_adt) = root_pred.self_ty().ty_adt_def()
3054+
&& self.tcx.is_diagnostic_item(sym::HashSet, root_adt.did())
3055+
&& self.tcx.is_diagnostic_item(sym::BuildHasher, pred.def_id()) =>
3056+
{
3057+
Some(span)
3058+
}
3059+
_ => None,
3060+
}
3061+
}) {
3062+
err.span_help(span, "you might have intended to use a HashMap instead");
3063+
}
30303064
}
30313065

30323066
let preds: Vec<_> = errors

‎compiler/rustc_span/src/symbol.rs‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -191,6 +191,7 @@ symbols! {
191191
Borrow,
192192
BorrowMut,
193193
Break,
194+
BuildHasher,
194195
C,
195196
CStr,
196197
C_dash_unwind: "C-unwind",

‎library/core/src/hash/mod.rs‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -633,6 +633,7 @@ impl<H: Hasher + ?Sized> Hasher for &mut H {
633633
///
634634
/// [`build_hasher`]: BuildHasher::build_hasher
635635
/// [`HashMap`]: ../../std/collections/struct.HashMap.html
636+
#[cfg_attr(not(test), rustc_diagnostic_item = "BuildHasher")]
636637
#[stable(since = "1.7.0", feature = "build_hasher")]
637638
pub trait BuildHasher {
638639
/// Type of the hasher that will be created.

‎tests/ui/hashmap/hashset_generics.rs‎

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,18 @@
1+
use std::collections::HashSet;
2+
3+
#[derive(PartialEq)]
4+
//~^ NOTE in this expansion of
5+
//~| NOTE in this expansion of
6+
//~| NOTE in this expansion of
7+
pub struct MyStruct {
8+
pub parameters: HashSet<String, String>,
9+
//~^ NOTE the foreign item type
10+
//~| ERROR binary operation
11+
}
12+
13+
fn main() {
14+
let h1 = HashSet::<usize, usize>::with_hasher(0);
15+
h1.insert(1);
16+
//~^ ERROR its trait bounds were not satisfied
17+
//~| NOTE the following trait bounds
18+
}

‎tests/ui/hashmap/hashset_generics.stderr‎

Lines changed: 40 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,40 @@
1+
error[E0369]: binary operation `==` cannot be applied to type `HashSet<String, String>`
2+
--> $DIR/hashset_generics.rs:8:5
3+
|
4+
LL | #[derive(PartialEq)]
5+
| --------- in this derive macro expansion
6+
...
7+
LL | pub parameters: HashSet<String, String>,
8+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
9+
|
10+
note: the foreign item type `String` doesn't implement `BuildHasher`
11+
--> $SRC_DIR/alloc/src/string.rs:LL:COL
12+
|
13+
= note: not implement `BuildHasher`
14+
help: you might have intended to use a HashMap instead
15+
--> $DIR/hashset_generics.rs:8:5
16+
|
17+
LL | #[derive(PartialEq)]
18+
| --------- in this derive macro expansion
19+
...
20+
LL | pub parameters: HashSet<String, String>,
21+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
22+
23+
error[E0599]: the method `insert` exists for struct `HashSet<usize, usize>`, but its trait bounds were not satisfied
24+
--> $DIR/hashset_generics.rs:15:8
25+
|
26+
LL | h1.insert(1);
27+
| ^^^^^^
28+
|
29+
= note: the following trait bounds were not satisfied:
30+
`usize: BuildHasher`
31+
help: you might have intended to use a HashMap instead
32+
--> $DIR/hashset_generics.rs:15:8
33+
|
34+
LL | h1.insert(1);
35+
| ^^^^^^
36+
37+
error: aborting due to 2 previous errors
38+
39+
Some errors have detailed explanations: E0369, E0599.
40+
For more information about an error, try `rustc --explain E0369`.

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