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Actually use the #[do_not_recommend] attribute if present

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This change tweaks the error message generation to actually use the
`#[do_not_recommend]` attribute if present by just skipping the marked
trait impl in favour of the parent impl. It also adds a compile test for
this behaviour. Without this change the test would output the following
error:

```
error[E0277]: the trait bound `&str: Expression` is not satisfied
  --> /home/weiznich/Documents/rust/rust/tests/ui/diagnostic_namespace/do_not_recommend.rs:53:15
   |
LL |     SelectInt.check("bar");
   |               ^^^^^ the trait `Expression` is not implemented for `&str`, which is required by `&str: AsExpression<Integer>`
   |
   = help: the following other types implement trait `Expression`:
             Bound<T>
             SelectInt
note: required for `&str` to implement `AsExpression<Integer>`
  --> /home/weiznich/Documents/rust/rust/tests/ui/diagnostic_namespace/do_not_recommend.rs:26:13
   |
LL | impl<T, ST> AsExpression<ST> for T
   |             ^^^^^^^^^^^^^^^^     ^
LL | where
LL |     T: Expression<SqlType = ST>,
   |        ------------------------ unsatisfied trait bound introduced here
```

Note how that mentions `&str: Expression` before and now mentions `&str:
AsExpression<Integer>` instead which is much more helpful for users.

Open points for further changes before stabilization:

* We likely want to move the attribute to the `#[diagnostic]` namespace
to relax the guarantees given?
* How does it interact with the new trait solver?
This commit is contained in:
Georg Semmler 2024-05-04 14:26:24 +02:00
parent bfa3635df9
commit 9b45cfdbdd
No known key found for this signature in database
GPG Key ID: A87BCEE5205CE489
11 changed files with 177 additions and 25 deletions
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26
compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs
View File

@ -422,6 +422,7 @@ fn report_selection_error(
ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_predicate)) => {
let trait_predicate = bound_predicate.rebind(trait_predicate);
let trait_predicate = self.resolve_vars_if_possible(trait_predicate);
let trait_predicate = self.apply_do_not_recommend(trait_predicate, &mut obligation);
// Let's use the root obligation as the main message, when we care about the
// most general case ("X doesn't implement Pattern<'_>") over the case that
@ -1003,6 +1004,31 @@ fn report_selection_error(
err.emit()
}
fn apply_do_not_recommend(
&self,
mut trait_predicate: ty::Binder<'tcx, ty::TraitPredicate<'tcx>>,
obligation: &'_ mut PredicateObligation<'tcx>,
) -> ty::Binder<'tcx, ty::TraitPredicate<'tcx>> {
let mut base_cause = obligation.cause.code().clone();
loop {
if let ObligationCauseCode::ImplDerived(ref c) = base_cause {
if self.tcx.has_attr(c.impl_or_alias_def_id, sym::do_not_recommend) {
let code = (*c.derived.parent_code).clone();
obligation.cause.map_code(|_| code);
obligation.predicate = c.derived.parent_trait_pred.upcast(self.tcx);
trait_predicate = c.derived.parent_trait_pred.clone();
}
}
if let Some((parent_cause, _parent_pred)) = base_cause.parent() {
base_cause = parent_cause.clone();
} else {
break;
}
}
trait_predicate
}
fn emit_specialized_closure_kind_error(
&self,
obligation: &PredicateObligation<'tcx>,

12
tests/ui/diagnostic_namespace/do_not_recommend/as_expression.current.stderr Normal file
View File

@ -0,0 +1,12 @@
error[E0277]: the trait bound `&str: AsExpression<Integer>` is not satisfied
--> $DIR/as_expression.rs:57:15
|
LL | SelectInt.check("bar");
| ^^^^^ the trait `AsExpression<Integer>` is not implemented for `&str`
|
= help: the trait `AsExpression<Text>` is implemented for `&str`
= help: for that trait implementation, expected `Text`, found `Integer`
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0277`.

21
tests/ui/diagnostic_namespace/do_not_recommend/as_expression.next.stderr Normal file
View File

@ -0,0 +1,21 @@
error[E0277]: the trait bound `&str: AsExpression<<SelectInt as Expression>::SqlType>` is not satisfied
--> $DIR/as_expression.rs:57:21
|
LL | SelectInt.check("bar");
| ----- ^^^^^ the trait `AsExpression<<SelectInt as Expression>::SqlType>` is not implemented for `&str`
| |
| required by a bound introduced by this call
|
= help: the trait `AsExpression<Text>` is implemented for `&str`
note: required by a bound in `Foo::check`
--> $DIR/as_expression.rs:48:12
|
LL | fn check<T>(&self, _: T) -> <T as AsExpression<<Self as Expression>::SqlType>>::Expression
| ----- required by a bound in this associated function
LL | where
LL | T: AsExpression<Self::SqlType>,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Foo::check`
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0277`.

60
tests/ui/diagnostic_namespace/do_not_recommend/as_expression.rs Normal file
View File

@ -0,0 +1,60 @@
//@ revisions: current next
//@ ignore-compare-mode-next-solver (explicit revisions)
//@[next] compile-flags: -Znext-solver
#![feature(do_not_recommend)]
pub trait Expression {
type SqlType;
}
pub trait AsExpression<ST> {
type Expression: Expression<SqlType = ST>;
}
pub struct Text;
pub struct Integer;
pub struct Bound<T>(T);
pub struct SelectInt;
impl Expression for SelectInt {
type SqlType = Integer;
}
impl<T> Expression for Bound<T> {
type SqlType = T;
}
#[do_not_recommend]
impl<T, ST> AsExpression<ST> for T
where
T: Expression<SqlType = ST>,
{
type Expression = T;
}
impl AsExpression<Integer> for i32 {
type Expression = Bound<Integer>;
}
impl AsExpression<Text> for &'_ str {
type Expression = Bound<Text>;
}
trait Foo: Expression + Sized {
fn check<T>(&self, _: T) -> <T as AsExpression<<Self as Expression>::SqlType>>::Expression
where
T: AsExpression<Self::SqlType>,
{
todo!()
}
}
impl<T> Foo for T where T: Expression {}
fn main() {
SelectInt.check("bar");
//[next]~^ ERROR the trait bound `&str: AsExpression<<SelectInt as Expression>::SqlType>` is not satisfied
//[current]~^^ ERROR the trait bound `&str: AsExpression<Integer>` is not satisfied
}

11
tests/ui/diagnostic_namespace/do_not_recommend/simple.current.stderr
View File

@ -1,16 +1,11 @@
error[E0277]: the trait bound `*mut (): Foo` is not satisfied
--> $DIR/simple.rs:19:17
--> $DIR/simple.rs:17:17
|
LL | needs_foo::<*mut ()>();
| ^^^^^^^ the trait `Send` is not implemented for `*mut ()`, which is required by `*mut (): Foo`
| ^^^^^^^ the trait `Foo` is not implemented for `*mut ()`
|
note: required for `*mut ()` to implement `Foo`
--> $DIR/simple.rs:10:9
|
LL | impl<T> Foo for T where T: Send {}
| ^^^ ^ ---- unsatisfied trait bound introduced here
note: required by a bound in `needs_foo`
--> $DIR/simple.rs:14:17
--> $DIR/simple.rs:12:17
|
LL | fn needs_foo<T: Foo>() {}
| ^^^ required by this bound in `needs_foo`

4
tests/ui/diagnostic_namespace/do_not_recommend/simple.next.stderr
View File

@ -1,11 +1,11 @@
error[E0277]: the trait bound `*mut (): Foo` is not satisfied
--> $DIR/simple.rs:19:17
--> $DIR/simple.rs:17:17
|
LL | needs_foo::<*mut ()>();
| ^^^^^^^ the trait `Foo` is not implemented for `*mut ()`
|
note: required by a bound in `needs_foo`
--> $DIR/simple.rs:14:17
--> $DIR/simple.rs:12:17
|
LL | fn needs_foo<T: Foo>() {}
| ^^^ required by this bound in `needs_foo`

5
tests/ui/diagnostic_namespace/do_not_recommend/simple.rs
View File

@ -8,8 +8,6 @@ trait Foo {}
#[do_not_recommend]
impl<T> Foo for T where T: Send {}
//[current]~^ NOTE required for `*mut ()` to implement `Foo`
//[current]~| NOTE unsatisfied trait bound introduced here
fn needs_foo<T: Foo>() {}
//~^ NOTE required by a bound in `needs_foo`
@ -18,6 +16,5 @@ fn needs_foo<T: Foo>() {}
fn main() {
needs_foo::<*mut ()>();
//~^ ERROR the trait bound `*mut (): Foo` is not satisfied
//[current]~| NOTE the trait `Send` is not implemented for `*mut ()`
//[next]~| NOTE the trait `Foo` is not implemented for `*mut ()`
//~| NOTE the trait `Foo` is not implemented for `*mut ()`
}

15
tests/ui/diagnostic_namespace/do_not_recommend/stacked.current.stderr Normal file
View File

@ -0,0 +1,15 @@
error[E0277]: the trait bound `(): Root` is not satisfied
--> $DIR/stacked.rs:19:18
|
LL | needs_root::<()>();
| ^^ the trait `Root` is not implemented for `()`
|
note: required by a bound in `needs_root`
--> $DIR/stacked.rs:16:18
|
LL | fn needs_root<T: Root>() {}
| ^^^^ required by this bound in `needs_root`
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0277`.

15
tests/ui/diagnostic_namespace/do_not_recommend/stacked.next.stderr Normal file
View File

@ -0,0 +1,15 @@
error[E0277]: the trait bound `(): Root` is not satisfied
--> $DIR/stacked.rs:19:18
|
LL | needs_root::<()>();
| ^^ the trait `Root` is not implemented for `()`
|
note: required by a bound in `needs_root`
--> $DIR/stacked.rs:16:18
|
LL | fn needs_root<T: Root>() {}
| ^^^^ required by this bound in `needs_root`
error: aborting due to 1 previous error
For more information about this error, try `rustc --explain E0277`.

21
tests/ui/diagnostic_namespace/do_not_recommend/stacked.rs Normal file
View File

@ -0,0 +1,21 @@
//@ revisions: current next
//@ ignore-compare-mode-next-solver (explicit revisions)
//@[next] compile-flags: -Znext-solver
#![feature(do_not_recommend)]
trait Root {}
trait DontRecommend {}
trait Other {}
#[do_not_recommend]
impl<T> Root for T where T: DontRecommend {}
impl<T> DontRecommend for T where T: Other {}
fn needs_root<T: Root>() {}
fn main() {
needs_root::<()>();
//~^ ERROR the trait bound `(): Root` is not satisfied
}

12
tests/ui/rfcs/rfc-2397-do-not-recommend/feature-gate-do_not_recommend.stderr
View File

@ -2,18 +2,8 @@ error[E0277]: the trait bound `u8: Bar` is not satisfied
--> $DIR/feature-gate-do_not_recommend.rs:19:11
|
LL | stuff(1u8);
| ----- ^^^ the trait `Foo` is not implemented for `u8`, which is required by `u8: Bar`
| |
| required by a bound introduced by this call
| ^^^ the trait `Bar` is not implemented for `u8`
|
= help: the trait `Foo` is implemented for `i32`
note: required for `u8` to implement `Bar`
--> $DIR/feature-gate-do_not_recommend.rs:13:14
|
LL | impl<T: Foo> Bar for T {
| --- ^^^ ^
| |
| unsatisfied trait bound introduced here
note: required by a bound in `stuff`
--> $DIR/feature-gate-do_not_recommend.rs:16:13
|