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rustc_resolve: Improve resolve_const_param_in_non_trivial_anon_const wording

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In some contexts, const expressions are OK. Add a `here` to the error
message to clarify this.
This commit is contained in:
Martin Nordholts 2025-06-07 12:41:56 +02:00
parent d00435f223
commit 4882ea4b3c
22 changed files with 78 additions and 35 deletions
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2
compiler/rustc_resolve/messages.ftl
View file

@ -119,7 +119,7 @@ resolve_const_param_in_enum_discriminant =
const parameters may not be used in enum discriminant values
resolve_const_param_in_non_trivial_anon_const =
const parameters may only be used as standalone arguments, i.e. `{$name}`
const parameters may only be used as standalone arguments here, i.e. `{$name}`
resolve_constructor_private_if_any_field_private =
a constructor is private if any of the fields is private

8
tests/ui/const-generics/const-arg-in-const-arg.min.stderr
View file

@ -13,7 +13,7 @@ error: generic parameters may not be used in const operations
LL | let _: [u8; bar::<N>()];
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -58,7 +58,7 @@ error: generic parameters may not be used in const operations
LL | let _ = [0; bar::<N>()];
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -112,7 +112,7 @@ error: generic parameters may not be used in const operations
LL | let _: Foo<{ bar::<N>() }>;
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -166,7 +166,7 @@ error: generic parameters may not be used in const operations
LL | let _ = Foo::<{ bar::<N>() }>;
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations

2
tests/ui/const-generics/defaults/complex-generic-default-expr.min.stderr
View file

@ -4,7 +4,7 @@ error: generic parameters may not be used in const operations
LL | struct Foo<const N: usize, const M: usize = { N + 1 }>;
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations

6
tests/ui/const-generics/early/const_arg_trivial_macro_expansion-4.stderr
View file

@ -7,7 +7,7 @@ LL | N
LL | fn foo<const N: usize>() -> Foo<{ arg!{} arg!{} }> { loop {} }
| ------ in this macro invocation
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
= note: this error originates in the macro `arg` (in Nightly builds, run with -Z macro-backtrace for more info)
@ -20,7 +20,7 @@ LL | N
LL | fn foo<const N: usize>() -> Foo<{ arg!{} arg!{} }> { loop {} }
| ------ in this macro invocation
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
= note: this error originates in the macro `arg` (in Nightly builds, run with -Z macro-backtrace for more info)
@ -30,7 +30,7 @@ error: generic parameters may not be used in const operations
LL | fn bar<const N: usize>() -> [(); { empty!{}; N }] { loop {} }
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: aborting due to 3 previous errors

8
tests/ui/const-generics/early/macro_rules-braces.stderr
View file

@ -26,7 +26,7 @@ error: generic parameters may not be used in const operations
LL | let _: foo!({{ N }});
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -35,7 +35,7 @@ error: generic parameters may not be used in const operations
LL | let _: bar!({ N });
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -44,7 +44,7 @@ error: generic parameters may not be used in const operations
LL | let _: baz!({{ N }});
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -53,7 +53,7 @@ error: generic parameters may not be used in const operations
LL | let _: biz!({ N });
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: aborting due to 6 previous errors

2
tests/ui/const-generics/early/trivial-const-arg-macro-nested-braces-2.stderr
View file

@ -7,7 +7,7 @@ LL | N
LL | fn foo<const N: usize>() -> A<{{ y!() }}> {
| ---- in this macro invocation
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
= note: this error originates in the macro `y` (in Nightly builds, run with -Z macro-backtrace for more info)

2
tests/ui/const-generics/early/trivial-const-arg-macro-nested-braces.stderr
View file

@ -7,7 +7,7 @@ LL | { N }
LL | fn foo<const N: usize>() -> A<{ y!() }> {
| ---- in this macro invocation
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
= note: this error originates in the macro `y` (in Nightly builds, run with -Z macro-backtrace for more info)

2
tests/ui/const-generics/early/trivial-const-arg-nested-braces.stderr
View file

@ -4,7 +4,7 @@ error: generic parameters may not be used in const operations
LL | fn foo<const N: usize>() -> A<{ { N } }> {
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: aborting due to 1 previous error

4
tests/ui/const-generics/generic_const_exprs/array-size-in-generic-struct-param.min.stderr
View file

@ -4,7 +4,7 @@ error: generic parameters may not be used in const operations
LL | struct ArithArrayLen<const N: usize>([u32; 0 + N]);
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -13,7 +13,7 @@ error: generic parameters may not be used in const operations
LL | arr: [u8; CFG.arr_size],
| ^^^ cannot perform const operation using `CFG`
|
= help: const parameters may only be used as standalone arguments, i.e. `CFG`
= help: const parameters may only be used as standalone arguments here, i.e. `CFG`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: `Config` is forbidden as the type of a const generic parameter

2
tests/ui/const-generics/generic_const_exprs/bad-multiply.stderr
View file

@ -4,7 +4,7 @@ error: generic parameters may not be used in const operations
LL | SmallVec<{ D * 2 }>:,
| ^ cannot perform const operation using `D`
|
= help: const parameters may only be used as standalone arguments, i.e. `D`
= help: const parameters may only be used as standalone arguments here, i.e. `D`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error[E0747]: constant provided when a type was expected

2
tests/ui/const-generics/generic_const_exprs/feature-gate-generic_const_exprs.stderr
View file

@ -4,7 +4,7 @@ error: generic parameters may not be used in const operations
LL | type Arr<const N: usize> = [u8; N - 1];
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: aborting due to 1 previous error

8
tests/ui/const-generics/generic_const_exprs/issue-72787.min.stderr
View file

@ -4,7 +4,7 @@ error: generic parameters may not be used in const operations
LL | Condition<{ LHS <= RHS }>: True
| ^^^ cannot perform const operation using `LHS`
|
= help: const parameters may only be used as standalone arguments, i.e. `LHS`
= help: const parameters may only be used as standalone arguments here, i.e. `LHS`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -13,7 +13,7 @@ error: generic parameters may not be used in const operations
LL | Condition<{ LHS <= RHS }>: True
| ^^^ cannot perform const operation using `RHS`
|
= help: const parameters may only be used as standalone arguments, i.e. `RHS`
= help: const parameters may only be used as standalone arguments here, i.e. `RHS`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -22,7 +22,7 @@ error: generic parameters may not be used in const operations
LL | IsLessOrEqual<{ 8 - I }, { 8 - J }>: True,
| ^ cannot perform const operation using `I`
|
= help: const parameters may only be used as standalone arguments, i.e. `I`
= help: const parameters may only be used as standalone arguments here, i.e. `I`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -31,7 +31,7 @@ error: generic parameters may not be used in const operations
LL | IsLessOrEqual<{ 8 - I }, { 8 - J }>: True,
| ^ cannot perform const operation using `J`
|
= help: const parameters may only be used as standalone arguments, i.e. `J`
= help: const parameters may only be used as standalone arguments here, i.e. `J`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: aborting due to 4 previous errors

2
tests/ui/const-generics/generic_const_exprs/issue-72819-generic-in-const-eval.min.stderr
View file

@ -4,7 +4,7 @@ error: generic parameters may not be used in const operations
LL | where Assert::<{N < usize::MAX / 2}>: IsTrue,
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: aborting due to 1 previous error

13
tests/ui/const-generics/generic_const_exprs/trivial-anon-const-use-cases.full.stderr Normal file
View file

@ -0,0 +1,13 @@
error: unconstrained generic constant
--> $DIR/trivial-anon-const-use-cases.rs:14:12
|
LL | stuff: [u8; { S + 1 }], // `S + 1` is NOT a valid const expression in this context.
| ^^^^^^^^^^^^^^^
|
help: try adding a `where` bound
|
LL | struct Y<const S: usize> where [(); { S + 1 }]: {
| ++++++++++++++++++++++
error: aborting due to 1 previous error

11
tests/ui/const-generics/generic_const_exprs/trivial-anon-const-use-cases.min.stderr Normal file
View file

@ -0,0 +1,11 @@
error: generic parameters may not be used in const operations
--> $DIR/trivial-anon-const-use-cases.rs:14:19
|
LL | stuff: [u8; { S + 1 }], // `S + 1` is NOT a valid const expression in this context.
| ^ cannot perform const operation using `S`
|
= help: const parameters may only be used as standalone arguments here, i.e. `S`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: aborting due to 1 previous error

19
tests/ui/const-generics/generic_const_exprs/trivial-anon-const-use-cases.rs Normal file
View file

@ -0,0 +1,19 @@
//! Regression test for <https://github.com/rust-lang/rust/issues/79429>.
//@ revisions: full min
#![cfg_attr(full, feature(generic_const_exprs))]
#![cfg_attr(full, allow(incomplete_features))]
struct X<const S: usize>;
impl<const S: usize> X<S> {
const LEN: usize = S + 1; // `S + 1` is a valid const expression in this context.
}
struct Y<const S: usize> {
stuff: [u8; { S + 1 }], // `S + 1` is NOT a valid const expression in this context.
//[min]~^ ERROR generic parameters may not be used in const operations
//[full]~^^ ERROR unconstrained generic constant
}
fn main() {}

2
tests/ui/const-generics/issues/issue-68366.min.stderr
View file

@ -4,7 +4,7 @@ error: generic parameters may not be used in const operations
LL | impl <const N: usize> Collatz<{Some(N)}> {}
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: `Option<usize>` is forbidden as the type of a const generic parameter

2
tests/ui/const-generics/issues/issue-76701-ty-param-in-const.stderr
View file

@ -13,7 +13,7 @@ error: generic parameters may not be used in const operations
LL | fn const_param<const N: usize>() -> [u8; N + 1] {
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: aborting due to 2 previous errors

2
tests/ui/const-generics/issues/issue-80375.stderr
View file

@ -4,7 +4,7 @@ error: generic parameters may not be used in const operations
LL | struct MyArray<const COUNT: usize>([u8; COUNT + 1]);
| ^^^^^ cannot perform const operation using `COUNT`
|
= help: const parameters may only be used as standalone arguments, i.e. `COUNT`
= help: const parameters may only be used as standalone arguments here, i.e. `COUNT`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: aborting due to 1 previous error

2
tests/ui/const-generics/legacy-const-generics-bad.stderr
View file

@ -16,7 +16,7 @@ error: generic parameters may not be used in const operations
LL | legacy_const_generics::foo(0, N + 1, 2);
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: aborting due to 2 previous errors

8
tests/ui/const-generics/min_const_generics/complex-expression.stderr
View file

@ -4,7 +4,7 @@ error: generic parameters may not be used in const operations
LL | struct Break0<const N: usize>([u8; { N + 1 }]);
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -13,7 +13,7 @@ error: generic parameters may not be used in const operations
LL | struct Break1<const N: usize>([u8; { { N } }]);
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -22,7 +22,7 @@ error: generic parameters may not be used in const operations
LL | let _: [u8; N + 1];
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -31,7 +31,7 @@ error: generic parameters may not be used in const operations
LL | let _ = [0; N + 1];
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations

4
tests/ui/const-generics/repeat_expr_hack_gives_right_generics.stderr
View file

@ -4,7 +4,7 @@ error: generic parameters may not be used in const operations
LL | bar::<{ [1; N] }>();
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: generic parameters may not be used in const operations
@ -13,7 +13,7 @@ error: generic parameters may not be used in const operations
LL | bar::<{ [1; { N + 1 }] }>();
| ^ cannot perform const operation using `N`
|
= help: const parameters may only be used as standalone arguments, i.e. `N`
= help: const parameters may only be used as standalone arguments here, i.e. `N`
= help: add `#![feature(generic_const_exprs)]` to allow generic const expressions
error: aborting due to 2 previous errors