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Reject early-bound params in the type of assoc const bindings
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5 files changed

+270
-10
lines changed

5 files changed

+270
-10
lines changed

‎compiler/rustc_hir_analysis/messages.ftl

Lines changed: 18 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -316,6 +316,22 @@ hir_analysis_opaque_captures_higher_ranked_lifetime = `impl Trait` cannot captur
316316
.label = `impl Trait` implicitly captures all lifetimes in scope
317317
.note = lifetime declared here
318318
319+
hir_analysis_param_in_ty_of_assoc_const_binding =
320+
the type of the associated constant `{$assoc_const}` must not depend on {$param_category ->
321+
[self] `Self`
322+
[synthetic] `impl Trait`
323+
*[normal] generic parameters
324+
}
325+
.label = its type must not depend on {$param_category ->
326+
[self] `Self`
327+
[synthetic] `impl Trait`
328+
*[normal] the {$param_def_kind} `{$param_name}`
329+
}
330+
.param_defined_here_label = {$param_category ->
331+
[synthetic] the `impl Trait` is specified here
332+
*[normal] the {$param_def_kind} `{$param_name}` is defined here
333+
}
334+
319335
hir_analysis_paren_sugar_attribute = the `#[rustc_paren_sugar]` attribute is a temporary means of controlling which traits can use parenthetical notation
320336
.help = add `#![feature(unboxed_closures)]` to the crate attributes to use it
321337
@@ -431,6 +447,8 @@ hir_analysis_transparent_non_zero_sized_enum = the variant of a transparent {$de
431447
.label = needs at most one field with non-trivial size or alignment, but has {$field_count}
432448
.labels = this field has non-zero size or requires alignment
433449
450+
hir_analysis_ty_of_assoc_const_binding_note = `{$assoc_const}` has type `{$ty}`
451+
434452
hir_analysis_ty_param_first_local = type parameter `{$param_ty}` must be covered by another type when it appears before the first local type (`{$local_type}`)
435453
.label = type parameter `{$param_ty}` must be covered by another type when it appears before the first local type (`{$local_type}`)
436454
.note = implementing a foreign trait is only possible if at least one of the types for which it is implemented is local, and no uncovered type parameters appear before that first local type

‎compiler/rustc_hir_analysis/src/astconv/bounds.rs

Lines changed: 98 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -1,12 +1,13 @@
1-
use rustc_data_structures::fx::FxIndexMap;
1+
use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
22
use rustc_errors::{codes::*, struct_span_code_err};
33
use rustc_hir as hir;
44
use rustc_hir::def::{DefKind, Res};
55
use rustc_hir::def_id::{DefId, LocalDefId};
6-
use rustc_middle::ty::{self as ty, Ty};
6+
use rustc_middle::ty::{self as ty, IsSuggestable, Ty, TyCtxt};
77
use rustc_span::symbol::Ident;
88
use rustc_span::{ErrorGuaranteed, Span};
99
use rustc_trait_selection::traits;
10+
use rustc_type_ir::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor};
1011
use smallvec::SmallVec;
1112

1213
use crate::astconv::{AstConv, OnlySelfBounds, PredicateFilter};
@@ -438,14 +439,8 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
438439
binding.kind
439440
{
440441
let ty = alias_ty.map_bound(|ty| tcx.type_of(ty.def_id).instantiate(tcx, ty.args));
441-
// Since the arguments passed to the alias type above may contain early-bound
442-
// generic parameters, the instantiated type may contain some as well.
443-
// Therefore wrap it in `EarlyBinder`.
444-
// FIXME(fmease): Reject escaping late-bound vars.
445-
tcx.feed_anon_const_type(
446-
anon_const.def_id,
447-
ty::EarlyBinder::bind(ty.skip_binder()),
448-
);
442+
let ty = check_assoc_const_binding_type(tcx, assoc_ident, ty, binding.hir_id);
443+
tcx.feed_anon_const_type(anon_const.def_id, ty::EarlyBinder::bind(ty));
449444
}
450445

451446
alias_ty
@@ -537,3 +532,96 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
537532
Ok(())
538533
}
539534
}
535+
536+
/// Detect and reject early-bound generic params in the type of associated const bindings.
537+
///
538+
/// FIXME(const_generics): This is a temporary and semi-artifical restriction until the
539+
/// arrival of *generic const generics*[^1].
540+
///
541+
/// It might actually be possible that we can already support early-bound generic params
542+
/// in such types if we just lifted some more checks in other places, too, for example
543+
/// inside [`ty::Const::from_anon_const`]. However, even if that were the case, we should
544+
/// probably gate this behind another feature flag.
545+
///
546+
/// [^1]: <https://github.com/rust-lang/project-const-generics/issues/28>.
547+
fn check_assoc_const_binding_type<'tcx>(
548+
tcx: TyCtxt<'tcx>,
549+
assoc_const: Ident,
550+
ty: ty::Binder<'tcx, Ty<'tcx>>,
551+
hir_id: hir::HirId,
552+
) -> Ty<'tcx> {
553+
// We can't perform the checks for early-bound params during name resolution unlike E0770
554+
// because this information depends on *type* resolution.
555+
556+
// FIXME(fmease): Reject escaping late-bound vars.
557+
let ty = ty.skip_binder();
558+
if !ty.has_param() {
559+
return ty;
560+
}
561+
562+
let mut collector = GenericParamCollector { params: Default::default() };
563+
ty.visit_with(&mut collector);
564+
565+
let mut guar = None;
566+
let ty_note = ty
567+
.make_suggestable(tcx, false)
568+
.map(|ty| crate::errors::TyOfAssocConstBindingNote { assoc_const, ty });
569+
570+
let enclosing_item_owner_id = tcx
571+
.hir()
572+
.parent_owner_iter(hir_id)
573+
.find_map(|(owner_id, parent)| parent.generics().map(|_| owner_id))
574+
.unwrap();
575+
let generics = tcx.generics_of(enclosing_item_owner_id);
576+
for index in collector.params {
577+
let param = generics.param_at(index as _, tcx);
578+
let is_self_param = param.name == rustc_span::symbol::kw::SelfUpper;
579+
guar.get_or_insert(tcx.dcx().emit_err(crate::errors::ParamInTyOfAssocConstBinding {
580+
span: assoc_const.span,
581+
assoc_const,
582+
param_name: param.name,
583+
param_def_kind: tcx.def_descr(param.def_id),
584+
param_category: if is_self_param {
585+
"self"
586+
} else if param.kind.is_synthetic() {
587+
"synthetic"
588+
} else {
589+
"normal"
590+
},
591+
param_defined_here_label:
592+
(!is_self_param).then(|| tcx.def_ident_span(param.def_id).unwrap()),
593+
ty_note,
594+
}));
595+
}
596+
597+
let guar = guar.unwrap_or_else(|| bug!("failed to find gen params in ty"));
598+
Ty::new_error(tcx, guar)
599+
}
600+
601+
struct GenericParamCollector {
602+
params: FxIndexSet<u32>,
603+
}
604+
605+
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for GenericParamCollector {
606+
fn visit_ty(&mut self, ty: Ty<'tcx>) -> Self::Result {
607+
if let ty::Param(param) = ty.kind() {
608+
self.params.insert(param.index);
609+
} else if ty.has_param() {
610+
ty.super_visit_with(self)
611+
}
612+
}
613+
614+
fn visit_region(&mut self, re: ty::Region<'tcx>) -> Self::Result {
615+
if let ty::ReEarlyParam(param) = re.kind() {
616+
self.params.insert(param.index);
617+
}
618+
}
619+
620+
fn visit_const(&mut self, ct: ty::Const<'tcx>) -> Self::Result {
621+
if let ty::ConstKind::Param(param) = ct.kind() {
622+
self.params.insert(param.index);
623+
} else if ct.has_param() {
624+
ct.super_visit_with(self)
625+
}
626+
}
627+
}

‎compiler/rustc_hir_analysis/src/errors.rs

Lines changed: 23 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -295,6 +295,29 @@ pub struct AssocTypeBindingNotAllowed {
295295
pub fn_trait_expansion: Option<ParenthesizedFnTraitExpansion>,
296296
}
297297

298+
#[derive(Diagnostic)]
299+
#[diag(hir_analysis_param_in_ty_of_assoc_const_binding)]
300+
pub(crate) struct ParamInTyOfAssocConstBinding<'tcx> {
301+
#[primary_span]
302+
#[label]
303+
pub span: Span,
304+
pub assoc_const: Ident,
305+
pub param_name: Symbol,
306+
pub param_def_kind: &'static str,
307+
pub param_category: &'static str,
308+
#[label(hir_analysis_param_defined_here_label)]
309+
pub param_defined_here_label: Option<Span>,
310+
#[subdiagnostic]
311+
pub ty_note: Option<TyOfAssocConstBindingNote<'tcx>>,
312+
}
313+
314+
#[derive(Subdiagnostic, Clone, Copy)]
315+
#[note(hir_analysis_ty_of_assoc_const_binding_note)]
316+
pub(crate) struct TyOfAssocConstBindingNote<'tcx> {
317+
pub assoc_const: Ident,
318+
pub ty: Ty<'tcx>,
319+
}
320+
298321
#[derive(Subdiagnostic)]
299322
#[help(hir_analysis_parenthesized_fn_trait_expansion)]
300323
pub struct ParenthesizedFnTraitExpansion {

‎tests/ui/associated-consts/assoc-const-eq-param-in-ty.rs

Lines changed: 55 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,55 @@
1+
// Regression test for issue #108271.
2+
// Detect and reject generic params in the type of assoc consts used in an equality bound.
3+
#![feature(associated_const_equality)]
4+
5+
trait Trait<'a, T: 'a, const N: usize> {
6+
const K: &'a [T; N];
7+
}
8+
9+
fn take0<'r, A: 'r, const Q: usize>(_: impl Trait<'r, A, Q, K = { loop {} }>) {}
10+
//~^ ERROR the type of the associated constant `K` must not depend on generic parameters
11+
//~| NOTE its type must not depend on the lifetime parameter `'r`
12+
//~| NOTE the lifetime parameter `'r` is defined here
13+
//~| NOTE `K` has type `&'r [A; Q]`
14+
//~| ERROR the type of the associated constant `K` must not depend on generic parameters
15+
//~| NOTE its type must not depend on the type parameter `A`
16+
//~| NOTE the type parameter `A` is defined here
17+
//~| NOTE `K` has type `&'r [A; Q]`
18+
//~| ERROR the type of the associated constant `K` must not depend on generic parameters
19+
//~| NOTE its type must not depend on the const parameter `Q`
20+
//~| NOTE the const parameter `Q` is defined here
21+
//~| NOTE `K` has type `&'r [A; Q]`
22+
23+
trait Project {
24+
const SELF: Self;
25+
}
26+
27+
fn take1(_: impl Project<SELF = {}>) {}
28+
//~^ ERROR the type of the associated constant `SELF` must not depend on `impl Trait`
29+
//~| NOTE its type must not depend on `impl Trait`
30+
//~| NOTE the `impl Trait` is specified here
31+
32+
fn take2<P: Project<SELF = {}>>(_: P) {}
33+
//~^ ERROR the type of the associated constant `SELF` must not depend on generic parameters
34+
//~| NOTE its type must not depend on the type parameter `P`
35+
//~| NOTE the type parameter `P` is defined here
36+
//~| NOTE `SELF` has type `P`
37+
38+
trait Iface<'r> {
39+
//~^ NOTE the lifetime parameter `'r` is defined here
40+
type Assoc<const Q: usize>: Trait<'r, Self, Q, K = { loop {} }>
41+
//~^ ERROR the type of the associated constant `K` must not depend on generic parameters
42+
//~| NOTE its type must not depend on the lifetime parameter `'r`
43+
//~| NOTE `K` has type `&'r [Self; Q]`
44+
//~| ERROR the type of the associated constant `K` must not depend on `Self`
45+
//~| NOTE its type must not depend on `Self`
46+
//~| NOTE `K` has type `&'r [Self; Q]`
47+
//~| ERROR the type of the associated constant `K` must not depend on generic parameters
48+
//~| NOTE its type must not depend on the const parameter `Q`
49+
//~| NOTE the const parameter `Q` is defined here
50+
//~| NOTE `K` has type `&'r [Self; Q]`
51+
where
52+
Self: Sized + 'r;
53+
}
54+
55+
fn main() {}

‎tests/ui/associated-consts/assoc-const-eq-param-in-ty.stderr

Lines changed: 76 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,76 @@
1+
error: the type of the associated constant `K` must not depend on generic parameters
2+
--> $DIR/assoc-const-eq-param-in-ty.rs:9:61
3+
|
4+
LL | fn take0<'r, A: 'r, const Q: usize>(_: impl Trait<'r, A, Q, K = { loop {} }>) {}
5+
| -- the lifetime parameter `'r` is defined here ^ its type must not depend on the lifetime parameter `'r`
6+
|
7+
= note: `K` has type `&'r [A; Q]`
8+
9+
error: the type of the associated constant `K` must not depend on generic parameters
10+
--> $DIR/assoc-const-eq-param-in-ty.rs:9:61
11+
|
12+
LL | fn take0<'r, A: 'r, const Q: usize>(_: impl Trait<'r, A, Q, K = { loop {} }>) {}
13+
| - the type parameter `A` is defined here ^ its type must not depend on the type parameter `A`
14+
|
15+
= note: `K` has type `&'r [A; Q]`
16+
17+
error: the type of the associated constant `K` must not depend on generic parameters
18+
--> $DIR/assoc-const-eq-param-in-ty.rs:9:61
19+
|
20+
LL | fn take0<'r, A: 'r, const Q: usize>(_: impl Trait<'r, A, Q, K = { loop {} }>) {}
21+
| - ^ its type must not depend on the const parameter `Q`
22+
| |
23+
| the const parameter `Q` is defined here
24+
|
25+
= note: `K` has type `&'r [A; Q]`
26+
27+
error: the type of the associated constant `SELF` must not depend on `impl Trait`
28+
--> $DIR/assoc-const-eq-param-in-ty.rs:27:26
29+
|
30+
LL | fn take1(_: impl Project<SELF = {}>) {}
31+
| -------------^^^^------
32+
| | |
33+
| | its type must not depend on `impl Trait`
34+
| the `impl Trait` is specified here
35+
36+
error: the type of the associated constant `SELF` must not depend on generic parameters
37+
--> $DIR/assoc-const-eq-param-in-ty.rs:32:21
38+
|
39+
LL | fn take2<P: Project<SELF = {}>>(_: P) {}
40+
| - ^^^^ its type must not depend on the type parameter `P`
41+
| |
42+
| the type parameter `P` is defined here
43+
|
44+
= note: `SELF` has type `P`
45+
46+
error: the type of the associated constant `K` must not depend on generic parameters
47+
--> $DIR/assoc-const-eq-param-in-ty.rs:40:52
48+
|
49+
LL | trait Iface<'r> {
50+
| -- the lifetime parameter `'r` is defined here
51+
LL |
52+
LL | type Assoc<const Q: usize>: Trait<'r, Self, Q, K = { loop {} }>
53+
| ^ its type must not depend on the lifetime parameter `'r`
54+
|
55+
= note: `K` has type `&'r [Self; Q]`
56+
57+
error: the type of the associated constant `K` must not depend on `Self`
58+
--> $DIR/assoc-const-eq-param-in-ty.rs:40:52
59+
|
60+
LL | type Assoc<const Q: usize>: Trait<'r, Self, Q, K = { loop {} }>
61+
| ^ its type must not depend on `Self`
62+
|
63+
= note: `K` has type `&'r [Self; Q]`
64+
65+
error: the type of the associated constant `K` must not depend on generic parameters
66+
--> $DIR/assoc-const-eq-param-in-ty.rs:40:52
67+
|
68+
LL | type Assoc<const Q: usize>: Trait<'r, Self, Q, K = { loop {} }>
69+
| - ^ its type must not depend on the const parameter `Q`
70+
| |
71+
| the const parameter `Q` is defined here
72+
|
73+
= note: `K` has type `&'r [Self; Q]`
74+
75+
error: aborting due to 8 previous errors
76+

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