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Allow ~const bounds on trait assoc functions #88418

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Aug 31, 2021
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4 changes: 2 additions & 2 deletions compiler/rustc_ast_passes/src/ast_validation.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1442,7 +1442,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
if !self.is_tilde_const_allowed {
self.err_handler()
.struct_span_err(bound.span(), "`~const` is not allowed here")
.note("only allowed on bounds on traits' associated types, const fns, const impls and its associated functions")
.note("only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions")
.emit();
}
}
Expand Down Expand Up @@ -1616,7 +1616,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
walk_list!(self, visit_ty, ty);
}
AssocItemKind::Fn(box FnKind(_, ref sig, ref generics, ref body))
if self.in_const_trait_impl =>
if self.in_const_trait_impl || ctxt == AssocCtxt::Trait =>
{
self.visit_vis(&item.vis);
self.visit_ident(item.ident);
Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -4,47 +4,47 @@ error: `~const` is not allowed here
LL | fn rpit() -> impl ~const T { S }
| ^^^^^^^^
|
= note: only allowed on bounds on traits' associated types, const fns, const impls and its associated functions
= note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions

error: `~const` is not allowed here
--> $DIR/tilde-const-invalid-places.rs:11:17
|
LL | fn apit(_: impl ~const T) {}
| ^^^^^^^^
|
= note: only allowed on bounds on traits' associated types, const fns, const impls and its associated functions
= note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions

error: `~const` is not allowed here
--> $DIR/tilde-const-invalid-places.rs:14:50
|
LL | fn rpit_assoc_bound() -> impl IntoIterator<Item: ~const T> { Some(S) }
| ^^^^^^^^
|
= note: only allowed on bounds on traits' associated types, const fns, const impls and its associated functions
= note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions

error: `~const` is not allowed here
--> $DIR/tilde-const-invalid-places.rs:17:48
|
LL | fn apit_assoc_bound(_: impl IntoIterator<Item: ~const T>) {}
| ^^^^^^^^
|
= note: only allowed on bounds on traits' associated types, const fns, const impls and its associated functions
= note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions

error: `~const` is not allowed here
--> $DIR/tilde-const-invalid-places.rs:20:15
|
LL | fn generic<P: ~const T>() {}
| ^^^^^^^^
|
= note: only allowed on bounds on traits' associated types, const fns, const impls and its associated functions
= note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions

error: `~const` is not allowed here
--> $DIR/tilde-const-invalid-places.rs:23:31
|
LL | fn where_clause<P>() where P: ~const T {}
| ^^^^^^^^
|
= note: only allowed on bounds on traits' associated types, const fns, const impls and its associated functions
= note: only allowed on bounds on traits' associated types and functions, const fns, const impls and its associated functions

error: `~const` and `?` are mutually exclusive
--> $DIR/tilde-const-invalid-places.rs:26:25
Expand Down
41 changes: 41 additions & 0 deletions src/test/ui/rfc-2632-const-trait-impl/trait-where-clause-run.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,41 @@
// run-pass

#![feature(const_trait_impl)]
#![feature(const_fn_trait_bound)]

trait Bar {
fn bar() -> u8;
}

trait Foo {
#[default_method_body_is_const]
fn foo() -> u8 where Self: ~const Bar {
<Self as Bar>::bar() * 6
}
}

struct NonConst;
struct Const;

impl Bar for NonConst {
fn bar() -> u8 {
3
}
}

impl Foo for NonConst {}

impl const Bar for Const {
fn bar() -> u8 {
4
}
}

impl const Foo for Const {}

fn main() {
const ANS1: u8 = Const::foo();
let ans2 = NonConst::foo();

assert_eq!(ANS1 + ans2, 42);
Comment on lines +37 to +40
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beautiful

}
Original file line number Diff line number Diff line change
@@ -0,0 +1,24 @@
// check-pass

#![feature(const_trait_impl)]
#![feature(const_fn_trait_bound)]

trait Foo {
fn bar() where Self: ~const Foo;
}

struct S;

impl Foo for S {
fn bar() {}
}

fn baz<T: Foo>() {
T::bar();
}

const fn qux<T: ~const Foo>() {
T::bar();
}

fn main() {}
40 changes: 40 additions & 0 deletions src/test/ui/rfc-2632-const-trait-impl/trait-where-clause.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,40 @@
#![feature(const_fn_trait_bound)]
#![feature(const_trait_impl)]

trait Bar {}

trait Foo {
fn a();
fn b() where Self: ~const Bar;
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A few more tests I think we should have:

  • where Self: ~const Foo
  • a const and a nonconst impl for such a trait
  • a monomorphic use that actually runs it

fn c<T: ~const Bar>();
}

const fn test1<T: ~const Foo + Bar>() {
T::a();
T::b();
//~^ ERROR the trait bound
T::c::<T>();
//~^ ERROR the trait bound
}

const fn test2<T: ~const Foo + ~const Bar>() {
T::a();
T::b();
T::c::<T>();
}

fn test3<T: Foo>() {
T::a();
T::b();
//~^ ERROR the trait bound
T::c::<T>();
//~^ ERROR the trait bound
}

fn test4<T: Foo + Bar>() {
T::a();
T::b();
T::c::<T>();
}

fn main() {}
67 changes: 67 additions & 0 deletions src/test/ui/rfc-2632-const-trait-impl/trait-where-clause.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,67 @@
error[E0277]: the trait bound `T: Bar` is not satisfied
--> $DIR/trait-where-clause.rs:14:5
|
LL | T::b();
| ^^^^ the trait `Bar` is not implemented for `T`
|
note: required by `Foo::b`
--> $DIR/trait-where-clause.rs:8:5
|
LL | fn b() where Self: ~const Bar;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: consider further restricting this bound
|
LL | const fn test1<T: ~const Foo + Bar + Bar>() {
| +++++

error[E0277]: the trait bound `T: Bar` is not satisfied
--> $DIR/trait-where-clause.rs:16:5
|
LL | T::c::<T>();
| ^^^^^^^^^ the trait `Bar` is not implemented for `T`
|
note: required by `Foo::c`
--> $DIR/trait-where-clause.rs:9:5
|
LL | fn c<T: ~const Bar>();
| ^^^^^^^^^^^^^^^^^^^^^^
help: consider further restricting this bound
|
LL | const fn test1<T: ~const Foo + Bar + Bar>() {
| +++++

error[E0277]: the trait bound `T: Bar` is not satisfied
--> $DIR/trait-where-clause.rs:28:5
|
LL | T::b();
| ^^^^ the trait `Bar` is not implemented for `T`
|
note: required by `Foo::b`
--> $DIR/trait-where-clause.rs:8:5
|
LL | fn b() where Self: ~const Bar;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: consider further restricting this bound
|
LL | fn test3<T: Foo + Bar>() {
| +++++

error[E0277]: the trait bound `T: Bar` is not satisfied
--> $DIR/trait-where-clause.rs:30:5
|
LL | T::c::<T>();
| ^^^^^^^^^ the trait `Bar` is not implemented for `T`
|
note: required by `Foo::c`
--> $DIR/trait-where-clause.rs:9:5
|
LL | fn c<T: ~const Bar>();
| ^^^^^^^^^^^^^^^^^^^^^^
help: consider further restricting this bound
|
LL | fn test3<T: Foo + Bar>() {
| +++++

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0277`.