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Rollup merge of #126403 - compiler-errors:better-type-errors, r=lcnr
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Actually report normalization-based type errors correctly for alias-relate obligations in new solver

We have some special casing to report type mismatch errors that come from projection predicates, but we don't do that for alias-relate obligations. This PR implements that. There's a bit of code duplication, but 🤷

Best reviewed without whitespace.

r? lcnr
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@jhpratt
jhpratt authored Jul 3, 2024
2 parents db59225 + ecdaff2 commit b1b9804
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Showing 9 changed files with 140 additions and 57 deletions.
149 changes: 101 additions & 48 deletions compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1586,60 +1586,113 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
}

self.probe(|_| {
let ocx = ObligationCtxt::new(self);

// try to find the mismatched types to report the error with.
//
// this can fail if the problem was higher-ranked, in which
// cause I have no idea for a good error message.
let bound_predicate = predicate.kind();
let (values, err) = if let ty::PredicateKind::Clause(ty::ClauseKind::Projection(data)) =
bound_predicate.skip_binder()
{
let data = self.instantiate_binder_with_fresh_vars(
obligation.cause.span,
infer::BoundRegionConversionTime::HigherRankedType,
bound_predicate.rebind(data),
);
let unnormalized_term = data.projection_term.to_term(self.tcx);
// FIXME(-Znext-solver): For diagnostic purposes, it would be nice
// to deeply normalize this type.
let normalized_term =
ocx.normalize(&obligation.cause, obligation.param_env, unnormalized_term);

debug!(?obligation.cause, ?obligation.param_env);

debug!(?normalized_term, data.ty = ?data.term);
let (values, err) = match bound_predicate.skip_binder() {
ty::PredicateKind::Clause(ty::ClauseKind::Projection(data)) => {
let ocx = ObligationCtxt::new(self);

let data = self.instantiate_binder_with_fresh_vars(
obligation.cause.span,
infer::BoundRegionConversionTime::HigherRankedType,
bound_predicate.rebind(data),
);
let unnormalized_term = data.projection_term.to_term(self.tcx);
// FIXME(-Znext-solver): For diagnostic purposes, it would be nice
// to deeply normalize this type.
let normalized_term =
ocx.normalize(&obligation.cause, obligation.param_env, unnormalized_term);

let is_normalized_term_expected = !matches!(
obligation.cause.code().peel_derives(),
ObligationCauseCode::WhereClause(..)
| ObligationCauseCode::WhereClauseInExpr(..)
| ObligationCauseCode::Coercion { .. }
);

let is_normalized_term_expected = !matches!(
obligation.cause.code().peel_derives(),
|ObligationCauseCode::WhereClause(..)| ObligationCauseCode::WhereClauseInExpr(
..
) | ObligationCauseCode::Coercion { .. }
);
let (expected, actual) = if is_normalized_term_expected {
(normalized_term, data.term)
} else {
(data.term, normalized_term)
};

let (expected, actual) = if is_normalized_term_expected {
(normalized_term, data.term)
} else {
(data.term, normalized_term)
};
// constrain inference variables a bit more to nested obligations from normalize so
// we can have more helpful errors.
//
// we intentionally drop errors from normalization here,
// since the normalization is just done to improve the error message.
let _ = ocx.select_where_possible();

// constrain inference variables a bit more to nested obligations from normalize so
// we can have more helpful errors.
//
// we intentionally drop errors from normalization here,
// since the normalization is just done to improve the error message.
let _ = ocx.select_where_possible();
if let Err(new_err) =
ocx.eq(&obligation.cause, obligation.param_env, expected, actual)
{
(
Some((
data.projection_term,
is_normalized_term_expected,
self.resolve_vars_if_possible(normalized_term),
data.term,
)),
new_err,
)
} else {
(None, error.err)
}
}
ty::PredicateKind::AliasRelate(lhs, rhs, _) => {
let derive_better_type_error =
|alias_term: ty::AliasTerm<'tcx>, expected_term: ty::Term<'tcx>| {
let ocx = ObligationCtxt::new(self);
let normalized_term = match expected_term.unpack() {
ty::TermKind::Ty(_) => self.next_ty_var(DUMMY_SP).into(),
ty::TermKind::Const(_) => self.next_const_var(DUMMY_SP).into(),
};
ocx.register_obligation(Obligation::new(
self.tcx,
ObligationCause::dummy(),
obligation.param_env,
ty::PredicateKind::NormalizesTo(ty::NormalizesTo {
alias: alias_term,
term: normalized_term,
}),
));
let _ = ocx.select_where_possible();
if let Err(terr) = ocx.eq(
&ObligationCause::dummy(),
obligation.param_env,
expected_term,
normalized_term,
) {
Some((terr, self.resolve_vars_if_possible(normalized_term)))
} else {
None
}
};

if let Err(new_err) =
ocx.eq(&obligation.cause, obligation.param_env, expected, actual)
{
(Some((data, is_normalized_term_expected, normalized_term, data.term)), new_err)
} else {
(None, error.err)
if let Some(lhs) = lhs.to_alias_term()
&& let Some((better_type_err, expected_term)) =
derive_better_type_error(lhs, rhs)
{
(
Some((lhs, true, self.resolve_vars_if_possible(expected_term), rhs)),
better_type_err,
)
} else if let Some(rhs) = rhs.to_alias_term()
&& let Some((better_type_err, expected_term)) =
derive_better_type_error(rhs, lhs)
{
(
Some((rhs, true, self.resolve_vars_if_possible(expected_term), lhs)),
better_type_err,
)
} else {
(None, error.err)
}
}
} else {
(None, error.err)
_ => (None, error.err),
};

let msg = values
Expand Down Expand Up @@ -1737,15 +1790,15 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {

fn maybe_detailed_projection_msg(
&self,
pred: ty::ProjectionPredicate<'tcx>,
projection_term: ty::AliasTerm<'tcx>,
normalized_ty: ty::Term<'tcx>,
expected_ty: ty::Term<'tcx>,
) -> Option<String> {
let trait_def_id = pred.projection_term.trait_def_id(self.tcx);
let self_ty = pred.projection_term.self_ty();
let trait_def_id = projection_term.trait_def_id(self.tcx);
let self_ty = projection_term.self_ty();

with_forced_trimmed_paths! {
if self.tcx.is_lang_item(pred.projection_term.def_id,LangItem::FnOnceOutput) {
if self.tcx.is_lang_item(projection_term.def_id, LangItem::FnOnceOutput) {
let fn_kind = self_ty.prefix_string(self.tcx);
let item = match self_ty.kind() {
ty::FnDef(def, _) => self.tcx.item_name(*def).to_string(),
Expand Down
5 changes: 4 additions & 1 deletion tests/ui/diagnostic_namespace/do_not_recommend/as_expression.next.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,10 @@ error[E0271]: type mismatch resolving `<SelectInt as Expression>::SqlType == Tex
--> $DIR/as_expression.rs:57:5
|
LL | SelectInt.check("bar");
| ^^^^^^^^^^^^^^^^^^^^^^ types differ
| ^^^^^^^^^^^^^^^^^^^^^^ expected `Integer`, found `Text`
|
= note: expected struct `Integer`
found struct `Text`

error: aborting due to 3 previous errors

Expand Down
5 changes: 4 additions & 1 deletion tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.nn.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,10 @@ error[E0271]: type mismatch resolving `<() as Index>::Output == &mut <() as Inde
--> $DIR/issue-100222.rs:34:12
|
LL | fn foo(&mut self, x: <Self as Index>::Output) -> <Self as Index>::Output
| ^^^^^^^^^ types differ
| ^^^^^^^^^ expected `()`, found `&mut <() as Index>::Output`
|
= note: expected unit type `()`
found mutable reference `&mut <() as Index>::Output`

error: aborting due to 1 previous error

Expand Down
5 changes: 4 additions & 1 deletion tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.ny.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,10 @@ error[E0271]: type mismatch resolving `<() as Index>::Output == &mut <() as Inde
--> $DIR/issue-100222.rs:25:12
|
LL | fn foo(&mut self, x: <Self as Index>::Output) -> <Self as Index>::Output
| ^^^^^^^^^ types differ
| ^^^^^^^^^ expected `()`, found `&mut <() as Index>::Output`
|
= note: expected unit type `()`
found mutable reference `&mut <() as Index>::Output`

error: aborting due to 1 previous error

Expand Down
5 changes: 4 additions & 1 deletion tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.yn.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,10 @@ error[E0271]: type mismatch resolving `<() as Index>::Output == &mut <() as Inde
--> $DIR/issue-100222.rs:34:12
|
LL | fn foo(&mut self, x: <Self as Index>::Output) -> <Self as Index>::Output
| ^^^^^^^^^ types differ
| ^^^^^^^^^ expected `()`, found `&mut <() as Index>::Output`
|
= note: expected unit type `()`
found mutable reference `&mut <() as Index>::Output`

error: aborting due to 1 previous error

Expand Down
5 changes: 4 additions & 1 deletion tests/ui/rfcs/rfc-2632-const-trait-impl/issue-100222.yy.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,10 @@ error[E0271]: type mismatch resolving `<() as Index>::Output == &mut <() as Inde
--> $DIR/issue-100222.rs:25:12
|
LL | fn foo(&mut self, x: <Self as Index>::Output) -> <Self as Index>::Output
| ^^^^^^^^^ types differ
| ^^^^^^^^^ expected `()`, found `&mut <() as Index>::Output`
|
= note: expected unit type `()`
found mutable reference `&mut <() as Index>::Output`

error: aborting due to 1 previous error

Expand Down
6 changes: 4 additions & 2 deletions tests/ui/traits/next-solver/async.fail.stderr
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Original file line number Diff line number Diff line change
@@ -1,11 +1,13 @@
error[E0271]: type mismatch resolving `<{async block@$DIR/async.rs:12:17: 12:22} as Future>::Output == i32`
error[E0271]: expected `{async block@$DIR/async.rs:12:17: 12:22}` to be a future that resolves to `i32`, but it resolves to `()`
--> $DIR/async.rs:12:17
|
LL | needs_async(async {});
| ----------- ^^^^^^^^ types differ
| ----------- ^^^^^^^^ expected `()`, found `i32`
| |
| required by a bound introduced by this call
|
= note: expected unit type `()`
found type `i32`
note: required by a bound in `needs_async`
--> $DIR/async.rs:8:31
|
Expand Down
2 changes: 1 addition & 1 deletion tests/ui/traits/next-solver/async.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ fn needs_async(_: impl Future<Output = i32>) {}
#[cfg(fail)]
fn main() {
needs_async(async {});
//[fail]~^ ERROR type mismatch
//[fail]~^ ERROR expected `{async block@$DIR/async.rs:12:17: 12:22}` to be a future that resolves to `i32`, but it resolves to `()`
}

#[cfg(pass)]
Expand Down
15 changes: 14 additions & 1 deletion tests/ui/traits/next-solver/more-object-bound.stderr
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Original file line number Diff line number Diff line change
@@ -1,9 +1,22 @@
error[E0271]: type mismatch resolving `<dyn Trait<A = A, B = B> as SuperTrait>::A == B`
--> $DIR/more-object-bound.rs:12:5
|
LL | fn transmute<A, B>(x: A) -> B {
| - -
| | |
| | expected type parameter
| | found type parameter
| found type parameter
| expected type parameter
LL | foo::<A, B, dyn Trait<A = A, B = B>>(x)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ types differ
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected type parameter `A`, found type parameter `B`
|
= note: expected type parameter `A`
found type parameter `B`
= note: a type parameter was expected, but a different one was found; you might be missing a type parameter or trait bound
= note: for more information, visit https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters
= note: a type parameter was expected, but a different one was found; you might be missing a type parameter or trait bound
= note: for more information, visit https://doc.rust-lang.org/book/ch10-02-traits.html#traits-as-parameters
= note: required because it appears within the type `dyn Trait<A = A, B = B>`
note: required by a bound in `foo`
--> $DIR/more-object-bound.rs:18:8
Expand Down

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