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Rollup merge of rust-lang#108063 - compiler-errors:associated-type-bo…
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…unds-in-bad-position, r=cjgillot

Ban associated type bounds in bad positions

We should not try to lower associated type bounds into TAITs in positions where `impl Trait` is not allowed (except for in `where` clauses, like `where T: Trait<Assoc: Bound>`).

This is achieved by using the same `rustc_ast_lowering` machinery as impl-trait does to characterize positions as universal/existential/disallowed.

Fixes rust-lang#106077

Split out the first commit into rust-lang#108066, since it's not really related.
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matthiaskrgr authored Feb 23, 2023
2 parents 0978711 + b14eb0c commit ef27e43
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3 changes: 3 additions & 0 deletions compiler/rustc_ast_lowering/locales/en-US.ftl
Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,9 @@ ast_lowering_remove_parentheses = remove these parentheses
ast_lowering_misplaced_impl_trait =
`impl Trait` only allowed in function and inherent method return types, not in {$position}
ast_lowering_misplaced_assoc_ty_binding =
associated type bounds are only allowed in where clauses and function signatures, not in {$position}
ast_lowering_rustc_box_attribute_error =
#[rustc_box] requires precisely one argument and no other attributes are allowed
Expand Down
8 changes: 8 additions & 0 deletions compiler/rustc_ast_lowering/src/errors.rs
Original file line number Diff line number Diff line change
Expand Up @@ -79,6 +79,14 @@ pub struct MisplacedImplTrait<'a> {
pub position: DiagnosticArgFromDisplay<'a>,
}

#[derive(Diagnostic)]
#[diag(ast_lowering_misplaced_assoc_ty_binding)]
pub struct MisplacedAssocTyBinding<'a> {
#[primary_span]
pub span: Span,
pub position: DiagnosticArgFromDisplay<'a>,
}

#[derive(Diagnostic, Clone, Copy)]
#[diag(ast_lowering_rustc_box_attribute_error)]
pub struct RustcBoxAttributeError {
Expand Down
135 changes: 73 additions & 62 deletions compiler/rustc_ast_lowering/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -288,31 +288,31 @@ enum ImplTraitPosition {
impl std::fmt::Display for ImplTraitPosition {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let name = match self {
ImplTraitPosition::Path => "path",
ImplTraitPosition::Variable => "variable binding",
ImplTraitPosition::Trait => "trait",
ImplTraitPosition::AsyncBlock => "async block",
ImplTraitPosition::Bound => "bound",
ImplTraitPosition::Generic => "generic",
ImplTraitPosition::ExternFnParam => "`extern fn` param",
ImplTraitPosition::ClosureParam => "closure param",
ImplTraitPosition::PointerParam => "`fn` pointer param",
ImplTraitPosition::FnTraitParam => "`Fn` trait param",
ImplTraitPosition::TraitParam => "trait method param",
ImplTraitPosition::ImplParam => "`impl` method param",
ImplTraitPosition::ExternFnReturn => "`extern fn` return",
ImplTraitPosition::ClosureReturn => "closure return",
ImplTraitPosition::PointerReturn => "`fn` pointer return",
ImplTraitPosition::FnTraitReturn => "`Fn` trait return",
ImplTraitPosition::TraitReturn => "trait method return",
ImplTraitPosition::ImplReturn => "`impl` method return",
ImplTraitPosition::GenericDefault => "generic parameter default",
ImplTraitPosition::ConstTy => "const type",
ImplTraitPosition::StaticTy => "static type",
ImplTraitPosition::AssocTy => "associated type",
ImplTraitPosition::FieldTy => "field type",
ImplTraitPosition::Cast => "cast type",
ImplTraitPosition::ImplSelf => "impl header",
ImplTraitPosition::Path => "paths",
ImplTraitPosition::Variable => "variable bindings",
ImplTraitPosition::Trait => "traits",
ImplTraitPosition::AsyncBlock => "async blocks",
ImplTraitPosition::Bound => "bounds",
ImplTraitPosition::Generic => "generics",
ImplTraitPosition::ExternFnParam => "`extern fn` params",
ImplTraitPosition::ClosureParam => "closure params",
ImplTraitPosition::PointerParam => "`fn` pointer params",
ImplTraitPosition::FnTraitParam => "`Fn` trait params",
ImplTraitPosition::TraitParam => "trait method params",
ImplTraitPosition::ImplParam => "`impl` method params",
ImplTraitPosition::ExternFnReturn => "`extern fn` return types",
ImplTraitPosition::ClosureReturn => "closure return types",
ImplTraitPosition::PointerReturn => "`fn` pointer return types",
ImplTraitPosition::FnTraitReturn => "`Fn` trait return types",
ImplTraitPosition::TraitReturn => "trait method return types",
ImplTraitPosition::ImplReturn => "`impl` method return types",
ImplTraitPosition::GenericDefault => "generic parameter defaults",
ImplTraitPosition::ConstTy => "const types",
ImplTraitPosition::StaticTy => "static types",
ImplTraitPosition::AssocTy => "associated types",
ImplTraitPosition::FieldTy => "field types",
ImplTraitPosition::Cast => "cast types",
ImplTraitPosition::ImplSelf => "impl headers",
};

write!(f, "{name}")
Expand Down Expand Up @@ -1002,8 +1002,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
} else {
self.arena.alloc(hir::GenericArgs::none())
};
let itctx_tait = &ImplTraitContext::TypeAliasesOpaqueTy;

let kind = match &constraint.kind {
AssocConstraintKind::Equality { term } => {
let term = match term {
Expand All @@ -1013,8 +1011,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
hir::TypeBindingKind::Equality { term }
}
AssocConstraintKind::Bound { bounds } => {
enum DesugarKind<'a> {
ImplTrait,
Error(&'a ImplTraitPosition),
Bound,
}

// Piggy-back on the `impl Trait` context to figure out the correct behavior.
let (desugar_to_impl_trait, itctx) = match itctx {
let desugar_kind = match itctx {
// We are in the return position:
//
// fn foo() -> impl Iterator<Item: Debug>
Expand All @@ -1023,7 +1027,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
//
// fn foo() -> impl Iterator<Item = impl Debug>
ImplTraitContext::ReturnPositionOpaqueTy { .. }
| ImplTraitContext::TypeAliasesOpaqueTy { .. } => (true, itctx),
| ImplTraitContext::TypeAliasesOpaqueTy { .. } => DesugarKind::ImplTrait,

// We are in the argument position, but within a dyn type:
//
Expand All @@ -1032,15 +1036,11 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// so desugar to
//
// fn foo(x: dyn Iterator<Item = impl Debug>)
ImplTraitContext::Universal if self.is_in_dyn_type => (true, itctx),
ImplTraitContext::Universal if self.is_in_dyn_type => DesugarKind::ImplTrait,

// In `type Foo = dyn Iterator<Item: Debug>` we desugar to
// `type Foo = dyn Iterator<Item = impl Debug>` but we have to override the
// "impl trait context" to permit `impl Debug` in this position (it desugars
// then to an opaque type).
//
// FIXME: this is only needed until `impl Trait` is allowed in type aliases.
ImplTraitContext::Disallowed(_) if self.is_in_dyn_type => (true, itctx_tait),
ImplTraitContext::Disallowed(position) if self.is_in_dyn_type => {
DesugarKind::Error(position)
}

// We are in the parameter position, but not within a dyn type:
//
Expand All @@ -1049,35 +1049,46 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
// 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`.
_ => (false, itctx),
_ => DesugarKind::Bound,
};

if desugar_to_impl_trait {
// 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();

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,
);
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.

hir::TypeBindingKind::Equality { term: 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);
let impl_trait_node_id = self.next_node_id();

hir::TypeBindingKind::Constraint { bounds }
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,
);

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);

hir::TypeBindingKind::Constraint { bounds }
}
DesugarKind::Error(position) => {
self.tcx.sess.emit_err(errors::MisplacedAssocTyBinding {
span: constraint.span,
position: DiagnosticArgFromDisplay(position),
});
let err_ty = &*self.arena.alloc(self.ty(constraint.span, hir::TyKind::Err));
hir::TypeBindingKind::Equality { term: err_ty.into() }
}
}
}
};
Expand Down
3 changes: 0 additions & 3 deletions compiler/rustc_ast_passes/locales/en-US.ftl
Original file line number Diff line number Diff line change
Expand Up @@ -11,9 +11,6 @@ ast_passes_forbidden_let_stable =
ast_passes_deprecated_where_clause_location =
where clause not allowed here
ast_passes_forbidden_assoc_constraint =
associated type bounds are not allowed within structs, enums, or unions
ast_passes_keyword_lifetime =
lifetimes cannot use keyword names
Expand Down
33 changes: 1 addition & 32 deletions compiler/rustc_ast_passes/src/ast_validation.rs
Original file line number Diff line number Diff line change
Expand Up @@ -71,10 +71,6 @@ struct AstValidator<'a> {
/// or `Foo::Bar<impl Trait>`
is_impl_trait_banned: bool,

/// Used to ban associated type bounds (i.e., `Type<AssocType: Bounds>`) in
/// certain positions.
is_assoc_ty_bound_banned: bool,

/// See [ForbiddenLetReason]
forbidden_let_reason: Option<ForbiddenLetReason>,

Expand Down Expand Up @@ -180,30 +176,12 @@ impl<'a> AstValidator<'a> {
}
}

fn with_banned_assoc_ty_bound(&mut self, f: impl FnOnce(&mut Self)) {
let old = mem::replace(&mut self.is_assoc_ty_bound_banned, true);
f(self);
self.is_assoc_ty_bound_banned = old;
}

fn with_impl_trait(&mut self, outer: Option<Span>, f: impl FnOnce(&mut Self)) {
let old = mem::replace(&mut self.outer_impl_trait, outer);
f(self);
self.outer_impl_trait = old;
}

fn visit_assoc_constraint_from_generic_args(&mut self, constraint: &'a AssocConstraint) {
match constraint.kind {
AssocConstraintKind::Equality { .. } => {}
AssocConstraintKind::Bound { .. } => {
if self.is_assoc_ty_bound_banned {
self.session.emit_err(ForbiddenAssocConstraint { span: constraint.span });
}
}
}
self.visit_assoc_constraint(constraint);
}

// Mirrors `visit::walk_ty`, but tracks relevant state.
fn walk_ty(&mut self, t: &'a Ty) {
match &t.kind {
Expand Down Expand Up @@ -1248,7 +1226,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
// are allowed to contain nested `impl Trait`.
AngleBracketedArg::Constraint(constraint) => {
self.with_impl_trait(None, |this| {
this.visit_assoc_constraint_from_generic_args(constraint);
this.visit_assoc_constraint(constraint);
});
}
}
Expand Down Expand Up @@ -1373,14 +1351,6 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
visit::walk_param_bound(self, bound)
}

fn visit_variant_data(&mut self, s: &'a VariantData) {
self.with_banned_assoc_ty_bound(|this| visit::walk_struct_def(this, s))
}

fn visit_enum_def(&mut self, enum_definition: &'a EnumDef) {
self.with_banned_assoc_ty_bound(|this| visit::walk_enum_def(this, enum_definition))
}

fn visit_fn(&mut self, fk: FnKind<'a>, span: Span, id: NodeId) {
// Only associated `fn`s can have `self` parameters.
let self_semantic = match fk.ctxt() {
Expand Down Expand Up @@ -1709,7 +1679,6 @@ pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) ->
outer_impl_trait: None,
disallow_tilde_const: None,
is_impl_trait_banned: false,
is_assoc_ty_bound_banned: false,
forbidden_let_reason: Some(ForbiddenLetReason::GenericForbidden),
lint_buffer: lints,
};
Expand Down
7 changes: 0 additions & 7 deletions compiler/rustc_ast_passes/src/errors.rs
Original file line number Diff line number Diff line change
Expand Up @@ -23,13 +23,6 @@ pub struct ForbiddenLetStable {
pub span: Span,
}

#[derive(Diagnostic)]
#[diag(ast_passes_forbidden_assoc_constraint)]
pub struct ForbiddenAssocConstraint {
#[primary_span]
pub span: Span,
}

#[derive(Diagnostic)]
#[diag(ast_passes_keyword_lifetime)]
pub struct KeywordLifetime {
Expand Down
2 changes: 1 addition & 1 deletion tests/ui/associated-consts/issue-105330.stderr
Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@ LL | fn main<A: TraitWAssocConst<A=32>>() {
= note: see issue #92827 <https://github.com/rust-lang/rust/issues/92827> for more information
= help: add `#![feature(associated_const_equality)]` to the crate attributes to enable

error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in impl header
error[E0562]: `impl Trait` only allowed in function and inherent method return types, not in impl headers
--> $DIR/issue-105330.rs:6:27
|
LL | impl TraitWAssocConst for impl Demo {
Expand Down
Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
#![feature(associated_type_bounds)]

trait B {
type AssocType;
}

fn f()
where
dyn for<'j> B<AssocType: 'j>:,
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures
{
}

fn main() {}
Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
error: associated type bounds are only allowed in where clauses and function signatures, not in bounds
--> $DIR/bad-universal-in-dyn-in-where-clause.rs:9:19
|
LL | dyn for<'j> B<AssocType: 'j>:,
| ^^^^^^^^^^^^^

error: aborting due to previous error

13 changes: 13 additions & 0 deletions tests/ui/associated-type-bounds/bad-universal-in-impl-sig.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
#![feature(associated_type_bounds)]

trait Trait {
type Item;
}

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

fn main() {}
Original file line number Diff line number Diff line change
@@ -0,0 +1,8 @@
error: associated type bounds are only allowed in where clauses and function signatures, not in impl headers
--> $DIR/bad-universal-in-impl-sig.rs:10:16
|
LL | impl dyn Trait<Item: Trait2> {}
| ^^^^^^^^^^^^

error: aborting due to previous error

22 changes: 9 additions & 13 deletions tests/ui/associated-type-bounds/inside-adt.rs
Original file line number Diff line number Diff line change
Expand Up @@ -3,28 +3,24 @@
use std::mem::ManuallyDrop;

struct S1 { f: dyn Iterator<Item: Copy> }
//~^ ERROR associated type bounds are not allowed within structs, enums, or unions
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures
struct S2 { f: Box<dyn Iterator<Item: Copy>> }
//~^ ERROR associated type bounds are not allowed within structs, enums, or unions
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures
struct S3 { f: dyn Iterator<Item: 'static> }
//~^ ERROR associated type bounds are not allowed within structs, enums, or unions
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures

enum E1 { V(dyn Iterator<Item: Copy>) }
//~^ ERROR associated type bounds are not allowed within structs, enums, or unions
//~| ERROR the size for values of type `(dyn Iterator<Item = impl Copy> + 'static)`
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures
enum E2 { V(Box<dyn Iterator<Item: Copy>>) }
//~^ ERROR associated type bounds are not allowed within structs, enums, or unions
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures
enum E3 { V(dyn Iterator<Item: 'static>) }
//~^ ERROR associated type bounds are not allowed within structs, enums, or unions
//~| ERROR the size for values of type `(dyn Iterator<Item = impl Sized + 'static> + 'static)`
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures

union U1 { f: ManuallyDrop<dyn Iterator<Item: Copy>> }
//~^ ERROR associated type bounds are not allowed within structs, enums, or unions
//~| ERROR the size for values of type `(dyn Iterator<Item = impl Copy> + 'static)`
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures
union U2 { f: ManuallyDrop<Box<dyn Iterator<Item: Copy>>> }
//~^ ERROR associated type bounds are not allowed within structs, enums, or unions
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures
union U3 { f: ManuallyDrop<dyn Iterator<Item: 'static>> }
//~^ ERROR associated type bounds are not allowed within structs, enums, or unions
//~| ERROR the size for values of type `(dyn Iterator<Item = impl Sized + 'static> + 'static)`
//~^ ERROR associated type bounds are only allowed in where clauses and function signatures

fn main() {}
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