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Remove support for associated_type_bound nested in dyn types #120719

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Feb 10, 2024
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7 changes: 4 additions & 3 deletions compiler/rustc_ast_lowering/messages.ftl
Original file line number Diff line number Diff line change
@@ -8,6 +8,10 @@ ast_lowering_arbitrary_expression_in_pattern =

ast_lowering_argument = argument

ast_lowering_assoc_ty_binding_in_dyn =
associated type bounds are not allowed in `dyn` types
.suggestion = use `impl Trait` to introduce a type instead

ast_lowering_assoc_ty_parentheses =
parenthesized generic arguments cannot be used in associated type constraints

@@ -100,9 +104,6 @@ ast_lowering_match_arm_with_no_body =
`match` arm with no body
.suggestion = add a body after the pattern

ast_lowering_misplaced_assoc_ty_binding =
associated type bounds are only allowed in where clauses and function signatures, not in {$position}

ast_lowering_misplaced_double_dot =
`..` patterns are not allowed here
.note = only allowed in tuple, tuple struct, and slice patterns
7 changes: 4 additions & 3 deletions compiler/rustc_ast_lowering/src/errors.rs
Original file line number Diff line number Diff line change
@@ -94,11 +94,12 @@ pub struct MisplacedImplTrait<'a> {
}

#[derive(Diagnostic)]
#[diag(ast_lowering_misplaced_assoc_ty_binding)]
pub struct MisplacedAssocTyBinding<'a> {
#[diag(ast_lowering_assoc_ty_binding_in_dyn)]
pub struct MisplacedAssocTyBinding {
#[primary_span]
pub span: Span,
pub position: DiagnosticArgFromDisplay<'a>,
#[suggestion(code = " = impl", applicability = "maybe-incorrect", style = "verbose")]
pub suggestion: Option<Span>,
}

#[derive(Diagnostic, Clone, Copy)]
116 changes: 30 additions & 86 deletions compiler/rustc_ast_lowering/src/lib.rs
Original file line number Diff line number Diff line change
@@ -197,7 +197,6 @@ trait ResolverAstLoweringExt {
fn get_label_res(&self, id: NodeId) -> Option<NodeId>;
fn get_lifetime_res(&self, id: NodeId) -> Option<LifetimeRes>;
fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)>;
fn remap_extra_lifetime_params(&mut self, from: NodeId, to: NodeId);
}

impl ResolverAstLoweringExt for ResolverAstLowering {
@@ -256,11 +255,6 @@ impl ResolverAstLoweringExt for ResolverAstLowering {
fn take_extra_lifetime_params(&mut self, id: NodeId) -> Vec<(Ident, NodeId, LifetimeRes)> {
self.extra_lifetime_params_map.remove(&id).unwrap_or_default()
}

fn remap_extra_lifetime_params(&mut self, from: NodeId, to: NodeId) {
let lifetimes = self.extra_lifetime_params_map.remove(&from).unwrap_or_default();
self.extra_lifetime_params_map.insert(to, lifetimes);
}
}

/// Context of `impl Trait` in code, which determines whether it is allowed in an HIR subtree,
@@ -1084,88 +1078,38 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
hir::TypeBindingKind::Equality { term }
}
AssocConstraintKind::Bound { bounds } => {
enum DesugarKind {
ImplTrait,
Error(ImplTraitPosition),
Bound,
}

// Piggy-back on the `impl Trait` context to figure out the correct behavior.
let desugar_kind = match itctx {
// in an argument, RPIT, or TAIT, if we are within a dyn type:
//
// fn foo(x: dyn Iterator<Item: Debug>)
//
// then desugar to:
//
// fn foo(x: dyn Iterator<Item = impl Debug>)
//
// This is because dyn traits must have all of their associated types specified.
ImplTraitContext::ReturnPositionOpaqueTy { .. }
| ImplTraitContext::TypeAliasesOpaqueTy { .. }
| ImplTraitContext::Universal
if self.is_in_dyn_type =>
{
DesugarKind::ImplTrait
}

ImplTraitContext::Disallowed(position) if self.is_in_dyn_type => {
DesugarKind::Error(position)
}

// We are in the parameter position, but not within a dyn type:
//
// fn foo(x: impl Iterator<Item: Debug>)
//
// so we leave it as is and this gets expanded in astconv to a bound like
// `<T as Iterator>::Item: Debug` where `T` is the type parameter for the
// `impl Iterator`.
_ => DesugarKind::Bound,
};

match desugar_kind {
DesugarKind::ImplTrait => {
// Desugar `AssocTy: Bounds` into `AssocTy = impl Bounds`. We do this by
// constructing the HIR for `impl bounds...` and then lowering that.

let impl_trait_node_id = self.next_node_id();
// Shift `impl Trait` lifetime captures from the associated type bound's
// node id to the opaque node id, so that the opaque can actually use
// these lifetime bounds.
self.resolver
.remap_extra_lifetime_params(constraint.id, impl_trait_node_id);

self.with_dyn_type_scope(false, |this| {
let node_id = this.next_node_id();
let ty = this.lower_ty(
&Ty {
id: node_id,
kind: TyKind::ImplTrait(impl_trait_node_id, bounds.clone()),
span: this.lower_span(constraint.span),
tokens: None,
},
itctx,
);
// Disallow ATB in dyn types
if self.is_in_dyn_type {
let suggestion = match itctx {
ImplTraitContext::ReturnPositionOpaqueTy { .. }
| ImplTraitContext::TypeAliasesOpaqueTy { .. }
| ImplTraitContext::Universal => {
let bound_end_span = constraint
.gen_args
.as_ref()
.map_or(constraint.ident.span, |args| args.span());
if bound_end_span.eq_ctxt(constraint.span) {
Some(self.tcx.sess.source_map().next_point(bound_end_span))
} else {
None
}
}
_ => None,
};

hir::TypeBindingKind::Equality { term: ty.into() }
})
}
DesugarKind::Bound => {
// Desugar `AssocTy: Bounds` into a type binding where the
// later desugars into a trait predicate.
let bounds = self.lower_param_bounds(bounds, itctx);
let guar = self.dcx().emit_err(errors::MisplacedAssocTyBinding {
span: constraint.span,
suggestion,
});
let err_ty =
&*self.arena.alloc(self.ty(constraint.span, hir::TyKind::Err(guar)));
hir::TypeBindingKind::Equality { term: err_ty.into() }
} else {
// Desugar `AssocTy: Bounds` into a type binding where the
// later desugars into a trait predicate.
let bounds = self.lower_param_bounds(bounds, itctx);

hir::TypeBindingKind::Constraint { bounds }
}
DesugarKind::Error(position) => {
let guar = self.dcx().emit_err(errors::MisplacedAssocTyBinding {
span: constraint.span,
position: DiagnosticArgFromDisplay(&position),
});
let err_ty =
&*self.arena.alloc(self.ty(constraint.span, hir::TyKind::Err(guar)));
hir::TypeBindingKind::Equality { term: err_ty.into() }
}
hir::TypeBindingKind::Constraint { bounds }
}
}
};
Original file line number Diff line number Diff line change
@@ -28,9 +28,9 @@ impl Bar for AssocNoCopy {

impl Thing for AssocNoCopy {
type Out = Box<dyn Bar<Assoc: Copy>>;
//~^ ERROR associated type bounds are not allowed in `dyn` types

fn func() -> Self::Out {
//~^ ERROR the trait bound `String: Copy` is not satisfied
Box::new(AssocNoCopy)
}
}
Original file line number Diff line number Diff line change
@@ -1,9 +1,13 @@
error[E0277]: the trait bound `String: Copy` is not satisfied
--> $DIR/assoc-type-eq-with-dyn-atb-fail.rs:32:18
error: associated type bounds are not allowed in `dyn` types
--> $DIR/assoc-type-eq-with-dyn-atb-fail.rs:30:28
|
LL | fn func() -> Self::Out {
| ^^^^^^^^^ the trait `Copy` is not implemented for `String`
LL | type Out = Box<dyn Bar<Assoc: Copy>>;
| ^^^^^^^^^^^
|
help: use `impl Trait` to introduce a type instead
|
LL | type Out = Box<dyn Bar<Assoc = impl Copy>>;
| ~~~~~~

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.
Original file line number Diff line number Diff line change
@@ -7,7 +7,7 @@ trait B {
fn f()
where
dyn for<'j> B<AssocType: 'j>:,
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures
//~^ ERROR associated type bounds are not allowed in `dyn` types
{
}

Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
error: associated type bounds are only allowed in where clauses and function signatures, not in bounds
error: associated type bounds are not allowed in `dyn` types
--> $DIR/bad-universal-in-dyn-in-where-clause.rs:9:19
|
LL | dyn for<'j> B<AssocType: 'j>:,
Original file line number Diff line number Diff line change
@@ -8,6 +8,6 @@ trait Trait2 {}

// It's not possible to insert a universal `impl Trait` here!
impl dyn Trait<Item: Trait2> {}
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures
//~^ ERROR associated type bounds are not allowed in `dyn` types

fn main() {}
Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
error: associated type bounds are only allowed in where clauses and function signatures, not in impl headers
error: associated type bounds are not allowed in `dyn` types
--> $DIR/bad-universal-in-impl-sig.rs:10:16
|
LL | impl dyn Trait<Item: Trait2> {}
7 changes: 0 additions & 7 deletions tests/ui/associated-type-bounds/duplicate.rs
Original file line number Diff line number Diff line change
@@ -261,11 +261,4 @@ trait TRA3 {
//~^ ERROR the value of the associated type `Item` in trait `Iterator` is already specified [E0719]
}

type TADyn1 = dyn Iterator<Item: Copy, Item: Send>;
//~^ ERROR the value of the associated type `Item` in trait `Iterator` is already specified [E0719]
type TADyn2 = Box<dyn Iterator<Item: Copy, Item: Copy>>;
//~^ ERROR the value of the associated type `Item` in trait `Iterator` is already specified [E0719]
type TADyn3 = dyn Iterator<Item: 'static, Item: 'static>;
//~^ ERROR the value of the associated type `Item` in trait `Iterator` is already specified [E0719]

fn main() {}
26 changes: 1 addition & 25 deletions tests/ui/associated-type-bounds/duplicate.stderr
Original file line number Diff line number Diff line change
@@ -6,30 +6,6 @@ LL | struct SI1<T: Iterator<Item: Copy, Item: Send>> {
| |
| `Item` bound here first

error[E0719]: the value of the associated type `Item` in trait `Iterator` is already specified
--> $DIR/duplicate.rs:264:40
|
LL | type TADyn1 = dyn Iterator<Item: Copy, Item: Send>;
| ---------- ^^^^^^^^^^ re-bound here
| |
| `Item` bound here first

error[E0719]: the value of the associated type `Item` in trait `Iterator` is already specified
--> $DIR/duplicate.rs:266:44
|
LL | type TADyn2 = Box<dyn Iterator<Item: Copy, Item: Copy>>;
| ---------- ^^^^^^^^^^ re-bound here
| |
| `Item` bound here first

error[E0719]: the value of the associated type `Item` in trait `Iterator` is already specified
--> $DIR/duplicate.rs:268:43
|
LL | type TADyn3 = dyn Iterator<Item: 'static, Item: 'static>;
| ------------- ^^^^^^^^^^^^^ re-bound here
| |
| `Item` bound here first

error[E0719]: the value of the associated type `Item` in trait `Iterator` is already specified
--> $DIR/duplicate.rs:11:36
|
@@ -631,7 +607,7 @@ LL | Self: Iterator<Item: 'static, Item: 'static>,
|
= note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`

error: aborting due to 75 previous errors
error: aborting due to 72 previous errors

Some errors have detailed explanations: E0282, E0719.
For more information about an error, try `rustc --explain E0282`.
66 changes: 0 additions & 66 deletions tests/ui/associated-type-bounds/dyn-impl-trait-type.rs

This file was deleted.

12 changes: 0 additions & 12 deletions tests/ui/associated-type-bounds/dyn-impl-trait-type.stderr

This file was deleted.

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