Skip to content

Commit

Permalink
Disallow impl autotrait for trait object
Browse files Browse the repository at this point in the history
  • Loading branch information
@dtolnay
dtolnay committed Jan 19, 2023
1 parent 19423b5 commit a247952
Show file tree
Hide file tree
Showing 6 changed files with 188 additions and 67 deletions.
4 changes: 2 additions & 2 deletions compiler/rustc_data_structures/src/sync.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -31,8 +31,8 @@ cfg_if! {
pub auto trait Send {}
pub auto trait Sync {}

impl<T: ?Sized> Send for T {}
impl<T: ?Sized> Sync for T {}
impl<T> Send for T {}
impl<T> Sync for T {}

#[macro_export]
macro_rules! rustc_erase_owner {
Expand Down
121 changes: 82 additions & 39 deletions compiler/rustc_hir_analysis/src/coherence/orphan.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -86,7 +86,7 @@ fn do_orphan_check_impl<'tcx>(
// struct B { }
// impl Foo for A { }
// impl Foo for B { }
// impl !Send for (A, B) { }
// impl !Foo for (A, B) { }
// ```
//
// This final impl is legal according to the orphan
Expand All @@ -99,50 +99,93 @@ fn do_orphan_check_impl<'tcx>(
tcx.trait_is_auto(trait_def_id)
);

if tcx.trait_is_auto(trait_def_id) && !trait_def_id.is_local() {
if tcx.trait_is_auto(trait_def_id) {
let self_ty = trait_ref.self_ty();
let opt_self_def_id = match *self_ty.kind() {
ty::Adt(self_def, _) => Some(self_def.did()),
ty::Foreign(did) => Some(did),
_ => None,
};
let self_ty_kind = self_ty.kind();

let msg = match opt_self_def_id {
// We only want to permit nominal types, but not *all* nominal types.
// They must be local to the current crate, so that people
// can't do `unsafe impl Send for Rc<SomethingLocal>` or
// `impl !Send for Box<SomethingLocalAndSend>`.
Some(self_def_id) => {
if self_def_id.is_local() {
None
} else {
Some((
format!(
"cross-crate traits with a default impl, like `{}`, \
can only be implemented for a struct/enum type \
defined in the current crate",
tcx.def_path_str(trait_def_id)
),
"can't implement cross-crate trait for type in another crate",
))
if trait_def_id.is_local() {
// If the auto-trait is local, almost anything goes.
//
// impl MyAuto for Rc<Something> {} // okay
// impl<T> !MyAuto for *const T {} // okay
// impl<T> MyAuto for T {} // okay
//
// But there is one important exception: implementing for a trait
// object is not allowed.
//
// impl MyAuto for dyn Trait {} // NOT OKAY
// impl<T: ?Sized> MyAuto for T {} // NOT OKAY
//
let problematic_kind = match self_ty_kind {
ty::Dynamic(..) => Some("trait object"),
ty::Param(..) if !self_ty.is_sized(tcx, tcx.param_env(def_id)) => {
Some("generic type")
}
_ => None,
};

if let Some(problematic_kind) = problematic_kind {
let msg = format!(
"traits with a default impl, like `{trait}`, \
cannot be implemented for {problematic_kind} `{self_ty}`",
trait = tcx.def_path_str(trait_def_id),
);
let label = format!(
"a trait object implements `{trait}` if and only if `{trait}` \
is one of the trait object's trait bounds",
trait = tcx.def_path_str(trait_def_id),
);
let reported = struct_span_err!(tcx.sess, sp, E0321, "{}", msg).note(label).emit();
return Err(reported);
}
_ => Some((
format!(
"cross-crate traits with a default impl, like `{}`, can \
} else {
// If the auto-trait is not local, it must only be getting
// implemented for a nominal type, and specifically one local to the
// current crate.
//
// impl<T> Sync for MyStruct<T> {} // okay
//
// impl Sync for Rc<MyStruct> {} // NOT OKAY
//
let opt_self_def_id = match *self_ty_kind {
ty::Adt(self_def, _) => Some(self_def.did()),
ty::Foreign(did) => Some(did),
_ => None,
};

let msg = match opt_self_def_id {
Some(self_def_id) => {
if self_def_id.is_local() {
None
} else {
Some((
format!(
"cross-crate traits with a default impl, like `{}`, \
can only be implemented for a struct/enum type \
defined in the current crate",
tcx.def_path_str(trait_def_id)
),
"can't implement cross-crate trait for type in another crate",
))
}
}
None => Some((
format!(
"cross-crate traits with a default impl, like `{}`, can \
only be implemented for a struct/enum type, not `{}`",
tcx.def_path_str(trait_def_id),
self_ty
),
"can't implement cross-crate trait with a default impl for \
non-struct/enum type",
)),
};
tcx.def_path_str(trait_def_id),
self_ty
),
"can't implement cross-crate trait with a default impl for \
non-struct/enum type",
)),
};

if let Some((msg, label)) = msg {
let reported =
struct_span_err!(tcx.sess, sp, E0321, "{}", msg).span_label(sp, label).emit();
return Err(reported);
if let Some((msg, label)) = msg {
let reported =
struct_span_err!(tcx.sess, sp, E0321, "{}", msg).span_label(sp, label).emit();
return Err(reported);
}
}
}

Expand Down
23 changes: 15 additions & 8 deletions tests/ui/coherence/coherence-impl-trait-for-marker-trait-negative.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -12,19 +12,26 @@ auto trait Marker2 {}
trait Object: Marker1 {}

// A supertrait marker is illegal...
impl !Marker1 for dyn Object + Marker2 { } //~ ERROR E0371
impl !Marker1 for dyn Object + Marker2 {} //~ ERROR E0371
//~^ ERROR 0321
// ...and also a direct component.
impl !Marker2 for dyn Object + Marker2 { } //~ ERROR E0371

// But implementing a marker if it is not present is OK.
impl !Marker2 for dyn Object {} // OK
impl !Marker2 for dyn Object + Marker2 {} //~ ERROR E0371
//~^ ERROR 0321

// A non-principal trait-object type is orphan even in its crate.
impl !Send for dyn Marker2 {} //~ ERROR E0117

// And impl'ing a remote marker for a local trait object is forbidden
// by one of these special orphan-like rules.
// Implementing a marker for a local trait object is forbidden by a special
// orphan-like rule.
impl !Marker2 for dyn Object {} //~ ERROR E0321
impl !Send for dyn Object {} //~ ERROR E0321
impl !Send for dyn Object + Marker2 {} //~ ERROR E0321

fn main() { }
// Blanket impl that applies to dyn Object is equally problematic.
auto trait Marker3 {}
impl<T: ?Sized> !Marker3 for T {} //~ ERROR E0321

auto trait Marker4 {}
impl<T> !Marker4 for T {} // okay

fn main() {}
42 changes: 37 additions & 5 deletions tests/ui/coherence/coherence-impl-trait-for-marker-trait-negative.stderr
View file
Original file line number Diff line number Diff line change
@@ -1,17 +1,41 @@
error[E0371]: the object type `(dyn Object + Marker2 + 'static)` automatically implements the trait `Marker1`
--> $DIR/coherence-impl-trait-for-marker-trait-negative.rs:15:1
|
LL | impl !Marker1 for dyn Object + Marker2 { }
LL | impl !Marker1 for dyn Object + Marker2 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `(dyn Object + Marker2 + 'static)` automatically implements trait `Marker1`

error[E0321]: traits with a default impl, like `Marker1`, cannot be implemented for trait object `(dyn Object + Marker2 + 'static)`
--> $DIR/coherence-impl-trait-for-marker-trait-negative.rs:15:1
|
LL | impl !Marker1 for dyn Object + Marker2 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: a trait object implements `Marker1` if and only if `Marker1` is one of the trait object's trait bounds

error[E0371]: the object type `(dyn Object + Marker2 + 'static)` automatically implements the trait `Marker2`
--> $DIR/coherence-impl-trait-for-marker-trait-negative.rs:17:1
--> $DIR/coherence-impl-trait-for-marker-trait-negative.rs:18:1
|
LL | impl !Marker2 for dyn Object + Marker2 { }
LL | impl !Marker2 for dyn Object + Marker2 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `(dyn Object + Marker2 + 'static)` automatically implements trait `Marker2`

error[E0321]: traits with a default impl, like `Marker2`, cannot be implemented for trait object `(dyn Object + Marker2 + 'static)`
--> $DIR/coherence-impl-trait-for-marker-trait-negative.rs:18:1
|
LL | impl !Marker2 for dyn Object + Marker2 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: a trait object implements `Marker2` if and only if `Marker2` is one of the trait object's trait bounds

error[E0321]: traits with a default impl, like `Marker2`, cannot be implemented for trait object `(dyn Object + 'static)`
--> $DIR/coherence-impl-trait-for-marker-trait-negative.rs:26:1
|
LL | impl !Marker2 for dyn Object {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: a trait object implements `Marker2` if and only if `Marker2` is one of the trait object's trait bounds

error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
--> $DIR/coherence-impl-trait-for-marker-trait-negative.rs:23:1
--> $DIR/coherence-impl-trait-for-marker-trait-negative.rs:22:1
|
LL | impl !Send for dyn Marker2 {}
| ^^^^^^^^^^^^^^^-----------
Expand All @@ -33,7 +57,15 @@ error[E0321]: cross-crate traits with a default impl, like `Send`, can only be i
LL | impl !Send for dyn Object + Marker2 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't implement cross-crate trait with a default impl for non-struct/enum type

error: aborting due to 5 previous errors
error[E0321]: traits with a default impl, like `Marker3`, cannot be implemented for generic type `T`
--> $DIR/coherence-impl-trait-for-marker-trait-negative.rs:32:1
|
LL | impl<T: ?Sized> !Marker3 for T {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: a trait object implements `Marker3` if and only if `Marker3` is one of the trait object's trait bounds

error: aborting due to 9 previous errors

Some errors have detailed explanations: E0117, E0321, E0371.
For more information about an error, try `rustc --explain E0117`.
23 changes: 15 additions & 8 deletions tests/ui/coherence/coherence-impl-trait-for-marker-trait-positive.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -12,19 +12,26 @@ auto trait Marker2 {}
trait Object: Marker1 {}

// A supertrait marker is illegal...
impl Marker1 for dyn Object + Marker2 { } //~ ERROR E0371
impl Marker1 for dyn Object + Marker2 {} //~ ERROR E0371
//~^ ERROR E0321
// ...and also a direct component.
impl Marker2 for dyn Object + Marker2 { } //~ ERROR E0371

// But implementing a marker if it is not present is OK.
impl Marker2 for dyn Object {} // OK
impl Marker2 for dyn Object + Marker2 {} //~ ERROR E0371
//~^ ERROR E0321

// A non-principal trait-object type is orphan even in its crate.
unsafe impl Send for dyn Marker2 {} //~ ERROR E0117

// And impl'ing a remote marker for a local trait object is forbidden
// by one of these special orphan-like rules.
// Implementing a marker for a local trait object is forbidden by a special
// orphan-like rule.
impl Marker2 for dyn Object {} //~ ERROR E0321
unsafe impl Send for dyn Object {} //~ ERROR E0321
unsafe impl Send for dyn Object + Marker2 {} //~ ERROR E0321

fn main() { }
// Blanket impl that applies to dyn Object is equally problematic.
auto trait Marker3 {}
impl<T: ?Sized> Marker3 for T {} //~ ERROR E0321

auto trait Marker4 {}
impl<T> Marker4 for T {} // okay

fn main() {}
42 changes: 37 additions & 5 deletions tests/ui/coherence/coherence-impl-trait-for-marker-trait-positive.stderr
View file
Original file line number Diff line number Diff line change
@@ -1,17 +1,41 @@
error[E0371]: the object type `(dyn Object + Marker2 + 'static)` automatically implements the trait `Marker1`
--> $DIR/coherence-impl-trait-for-marker-trait-positive.rs:15:1
|
LL | impl Marker1 for dyn Object + Marker2 { }
LL | impl Marker1 for dyn Object + Marker2 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `(dyn Object + Marker2 + 'static)` automatically implements trait `Marker1`

error[E0321]: traits with a default impl, like `Marker1`, cannot be implemented for trait object `(dyn Object + Marker2 + 'static)`
--> $DIR/coherence-impl-trait-for-marker-trait-positive.rs:15:1
|
LL | impl Marker1 for dyn Object + Marker2 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: a trait object implements `Marker1` if and only if `Marker1` is one of the trait object's trait bounds

error[E0371]: the object type `(dyn Object + Marker2 + 'static)` automatically implements the trait `Marker2`
--> $DIR/coherence-impl-trait-for-marker-trait-positive.rs:17:1
--> $DIR/coherence-impl-trait-for-marker-trait-positive.rs:18:1
|
LL | impl Marker2 for dyn Object + Marker2 { }
LL | impl Marker2 for dyn Object + Marker2 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `(dyn Object + Marker2 + 'static)` automatically implements trait `Marker2`

error[E0321]: traits with a default impl, like `Marker2`, cannot be implemented for trait object `(dyn Object + Marker2 + 'static)`
--> $DIR/coherence-impl-trait-for-marker-trait-positive.rs:18:1
|
LL | impl Marker2 for dyn Object + Marker2 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: a trait object implements `Marker2` if and only if `Marker2` is one of the trait object's trait bounds

error[E0321]: traits with a default impl, like `Marker2`, cannot be implemented for trait object `(dyn Object + 'static)`
--> $DIR/coherence-impl-trait-for-marker-trait-positive.rs:26:1
|
LL | impl Marker2 for dyn Object {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: a trait object implements `Marker2` if and only if `Marker2` is one of the trait object's trait bounds

error[E0117]: only traits defined in the current crate can be implemented for arbitrary types
--> $DIR/coherence-impl-trait-for-marker-trait-positive.rs:23:1
--> $DIR/coherence-impl-trait-for-marker-trait-positive.rs:22:1
|
LL | unsafe impl Send for dyn Marker2 {}
| ^^^^^^^^^^^^^^^^^^^^^-----------
Expand All @@ -33,7 +57,15 @@ error[E0321]: cross-crate traits with a default impl, like `Send`, can only be i
LL | unsafe impl Send for dyn Object + Marker2 {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't implement cross-crate trait with a default impl for non-struct/enum type

error: aborting due to 5 previous errors
error[E0321]: traits with a default impl, like `Marker3`, cannot be implemented for generic type `T`
--> $DIR/coherence-impl-trait-for-marker-trait-positive.rs:32:1
|
LL | impl<T: ?Sized> Marker3 for T {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: a trait object implements `Marker3` if and only if `Marker3` is one of the trait object's trait bounds

error: aborting due to 9 previous errors

Some errors have detailed explanations: E0117, E0321, E0371.
For more information about an error, try `rustc --explain E0117`.

0 comments on commit a247952

Please sign in to comment.