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Auto merge of rust-lang#95680 - Dylan-DPC:rollup-7jldtnz, r=Dylan-DPC
Rollup of 4 pull requests Successful merges: - rust-lang#95525 (Suggest derivable trait on E0277 error) - rust-lang#95654 (diagnostics: use correct span for const generics) - rust-lang#95660 (Update panic docs to make it clearer when to use panic vs Result) - rust-lang#95670 (Refactor: remove unused function parameters) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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‎compiler/rustc_ast_lowering/src/lib.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -2068,7 +2068,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
20682068
hir::GenericParam {
20692069
hir_id,
20702070
name,
2071-
span: self.lower_span(param.ident.span),
2071+
span: self.lower_span(param.span()),
20722072
pure_wrt_drop: self.sess.contains_name(&param.attrs, sym::may_dangle),
20732073
bounds: self.arena.alloc_from_iter(bounds),
20742074
kind,

‎compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

+3-12
Original file line numberDiff line numberDiff line change
@@ -772,14 +772,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
772772
Some((issued_span, span)),
773773
);
774774

775-
self.suggest_using_local_if_applicable(
776-
&mut err,
777-
location,
778-
(place, span),
779-
gen_borrow_kind,
780-
issued_borrow,
781-
explanation,
782-
);
775+
self.suggest_using_local_if_applicable(&mut err, location, issued_borrow, explanation);
783776

784777
err
785778
}
@@ -789,8 +782,6 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
789782
&self,
790783
err: &mut Diagnostic,
791784
location: Location,
792-
(place, span): (Place<'tcx>, Span),
793-
gen_borrow_kind: BorrowKind,
794785
issued_borrow: &BorrowData<'tcx>,
795786
explanation: BorrowExplanation,
796787
) {
@@ -822,7 +813,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
822813
return;
823814
};
824815
let inner_param_uses = find_all_local_uses::find(self.body, inner_param.local);
825-
let Some((inner_call_loc,inner_call_term)) = inner_param_uses.into_iter().find_map(|loc| {
816+
let Some((inner_call_loc, inner_call_term)) = inner_param_uses.into_iter().find_map(|loc| {
826817
let Either::Right(term) = self.body.stmt_at(loc) else {
827818
debug!("{:?} is a statement, so it can't be a call", loc);
828819
return None;
@@ -833,7 +824,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
833824
};
834825
debug!("checking call args for uses of inner_param: {:?}", args);
835826
if args.contains(&Operand::Move(inner_param)) {
836-
Some((loc,term))
827+
Some((loc, term))
837828
} else {
838829
None
839830
}

‎compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

+1
Original file line numberDiff line numberDiff line change
@@ -540,6 +540,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
540540
);
541541
self.note_version_mismatch(&mut err, &trait_ref);
542542
self.suggest_remove_await(&obligation, &mut err);
543+
self.suggest_derive(&obligation, &mut err, trait_predicate);
543544

544545
if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
545546
self.suggest_await_before_try(

‎compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

+69
Original file line numberDiff line numberDiff line change
@@ -189,6 +189,13 @@ pub trait InferCtxtExt<'tcx> {
189189
err: &mut Diagnostic,
190190
trait_ref: &ty::PolyTraitRef<'tcx>,
191191
);
192+
193+
fn suggest_derive(
194+
&self,
195+
obligation: &PredicateObligation<'tcx>,
196+
err: &mut Diagnostic,
197+
trait_pred: ty::PolyTraitPredicate<'tcx>,
198+
);
192199
}
193200

194201
fn predicate_constraint(generics: &hir::Generics<'_>, pred: String) -> (Span, String) {
@@ -2651,6 +2658,68 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
26512658
_ => {}
26522659
}
26532660
}
2661+
2662+
fn suggest_derive(
2663+
&self,
2664+
obligation: &PredicateObligation<'tcx>,
2665+
err: &mut Diagnostic,
2666+
trait_pred: ty::PolyTraitPredicate<'tcx>,
2667+
) {
2668+
let Some(diagnostic_name) = self.tcx.get_diagnostic_name(trait_pred.def_id()) else {
2669+
return;
2670+
};
2671+
let (adt, substs) = match trait_pred.skip_binder().self_ty().kind() {
2672+
ty::Adt(adt, substs) if adt.did().is_local() => (adt, substs),
2673+
_ => return,
2674+
};
2675+
let can_derive = {
2676+
let is_derivable_trait = match diagnostic_name {
2677+
sym::Default => !adt.is_enum(),
2678+
sym::PartialEq | sym::PartialOrd => {
2679+
let rhs_ty = trait_pred.skip_binder().trait_ref.substs.type_at(1);
2680+
trait_pred.skip_binder().self_ty() == rhs_ty
2681+
}
2682+
sym::Eq | sym::Ord | sym::Clone | sym::Copy | sym::Hash | sym::Debug => true,
2683+
_ => false,
2684+
};
2685+
is_derivable_trait &&
2686+
// Ensure all fields impl the trait.
2687+
adt.all_fields().all(|field| {
2688+
let field_ty = field.ty(self.tcx, substs);
2689+
let trait_substs = match diagnostic_name {
2690+
sym::PartialEq | sym::PartialOrd => {
2691+
self.tcx.mk_substs_trait(field_ty, &[field_ty.into()])
2692+
}
2693+
_ => self.tcx.mk_substs_trait(field_ty, &[]),
2694+
};
2695+
let trait_pred = trait_pred.map_bound_ref(|tr| ty::TraitPredicate {
2696+
trait_ref: ty::TraitRef {
2697+
substs: trait_substs,
2698+
..trait_pred.skip_binder().trait_ref
2699+
},
2700+
..*tr
2701+
});
2702+
let field_obl = Obligation::new(
2703+
obligation.cause.clone(),
2704+
obligation.param_env,
2705+
trait_pred.to_predicate(self.tcx),
2706+
);
2707+
self.predicate_must_hold_modulo_regions(&field_obl)
2708+
})
2709+
};
2710+
if can_derive {
2711+
err.span_suggestion_verbose(
2712+
self.tcx.def_span(adt.did()).shrink_to_lo(),
2713+
&format!(
2714+
"consider annotating `{}` with `#[derive({})]`",
2715+
trait_pred.skip_binder().self_ty(),
2716+
diagnostic_name.to_string(),
2717+
),
2718+
format!("#[derive({})]\n", diagnostic_name.to_string()),
2719+
Applicability::MaybeIncorrect,
2720+
);
2721+
}
2722+
}
26542723
}
26552724

26562725
/// Collect all the returned expressions within the input expression.

‎library/core/src/macros/panic.md

+19-7
Original file line numberDiff line numberDiff line change
@@ -1,8 +1,7 @@
11
Panics the current thread.
22

33
This allows a program to terminate immediately and provide feedback
4-
to the caller of the program. `panic!` should be used when a program reaches
5-
an unrecoverable state.
4+
to the caller of the program.
65

76
This macro is the perfect way to assert conditions in example code and in
87
tests. `panic!` is closely tied with the `unwrap` method of both
@@ -21,13 +20,25 @@ Inside the hook a panic can be accessed as a `&dyn Any + Send`,
2120
which contains either a `&str` or `String` for regular `panic!()` invocations.
2221
To panic with a value of another other type, [`panic_any`] can be used.
2322

24-
[`Result`] enum is often a better solution for recovering from errors than
25-
using the `panic!` macro. This macro should be used to avoid proceeding using
26-
incorrect values, such as from external sources. Detailed information about
27-
error handling is found in the [book].
28-
2923
See also the macro [`compile_error!`], for raising errors during compilation.
3024

25+
# When to use `panic!` vs `Result`
26+
27+
The Rust model of error handling groups errors into two major categories:
28+
recoverable and unrecoverable errors. For a recoverable error, such as a file
29+
not found error, it’s reasonable to report the problem to the user and retry
30+
the operation. Unrecoverable errors are always symptoms of bugs, like trying to
31+
access a location beyond the end of an array.
32+
33+
The Rust language and standard library provides `Result` and `panic!` as parts
34+
of two complementary systems for representing, reporting, propagating, reacting
35+
to, and discarding errors for in these two categories.
36+
37+
The `panic!` macro is provided to represent unrecoverable errors, whereas the
38+
`Result` enum is provided to represent recoverable errors. For more detailed
39+
information about error handling check out the [book] or the [`std::result`]
40+
module docs.
41+
3142
[ounwrap]: Option::unwrap
3243
[runwrap]: Result::unwrap
3344
[`std::panic::set_hook()`]: ../std/panic/fn.set_hook.html
@@ -36,6 +47,7 @@ See also the macro [`compile_error!`], for raising errors during compilation.
3647
[`Any`]: crate::any::Any
3748
[`format!`]: ../std/macro.format.html
3849
[book]: ../book/ch09-00-error-handling.html
50+
[`std::result`]: ../std/result/index.html
3951

4052
# Current implementation
4153

‎src/test/ui/array-slice-vec/repeat_empty_ok.stderr

+8
Original file line numberDiff line numberDiff line change
@@ -5,6 +5,10 @@ LL | let headers = [Header{value: &[]}; 128];
55
| ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `Header<'_>`
66
|
77
= note: the `Copy` trait is required because the repeated element will be copied
8+
help: consider annotating `Header<'_>` with `#[derive(Copy)]`
9+
|
10+
LL | #[derive(Copy)]
11+
|
812

913
error[E0277]: the trait bound `Header<'_>: Copy` is not satisfied
1014
--> $DIR/repeat_empty_ok.rs:13:19
@@ -13,6 +17,10 @@ LL | let headers = [Header{value: &[0]}; 128];
1317
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `Header<'_>`
1418
|
1519
= note: the `Copy` trait is required because the repeated element will be copied
20+
help: consider annotating `Header<'_>` with `#[derive(Copy)]`
21+
|
22+
LL | #[derive(Copy)]
23+
|
1624

1725
error: aborting due to 2 previous errors
1826

‎src/test/ui/associated-types/defaults-suitability.stderr

+8
Original file line numberDiff line numberDiff line change
@@ -9,6 +9,10 @@ note: required by a bound in `Tr::Ty`
99
|
1010
LL | type Ty: Clone = NotClone;
1111
| ^^^^^ required by this bound in `Tr::Ty`
12+
help: consider annotating `NotClone` with `#[derive(Clone)]`
13+
|
14+
LL | #[derive(Clone)]
15+
|
1216

1317
error[E0277]: the trait bound `NotClone: Clone` is not satisfied
1418
--> $DIR/defaults-suitability.rs:22:15
@@ -24,6 +28,10 @@ LL | Self::Ty: Clone,
2428
LL | {
2529
LL | type Ty = NotClone;
2630
| -- required by a bound in this
31+
help: consider annotating `NotClone` with `#[derive(Clone)]`
32+
|
33+
LL | #[derive(Clone)]
34+
|
2735

2836
error[E0277]: the trait bound `T: Clone` is not satisfied
2937
--> $DIR/defaults-suitability.rs:28:23

‎src/test/ui/associated-types/trait-with-supertraits-needing-sized-self.stderr

+1-1
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@ note: required by a bound in `Add`
88
--> $SRC_DIR/core/src/ops/arith.rs:LL:COL
99
|
1010
LL | pub trait Add<Rhs = Self> {
11-
| ^^^ required by this bound in `Add`
11+
| ^^^^^^^^^^ required by this bound in `Add`
1212
help: consider further restricting `Self`
1313
|
1414
LL | trait ArithmeticOps: Add<Output=Self> + Sub<Output=Self> + Mul<Output=Self> + Div<Output=Self> + Sized {}

‎src/test/ui/async-await/issues/issue-78654.full.stderr

+2-2
Original file line numberDiff line numberDiff line change
@@ -5,10 +5,10 @@ LL | impl<const H: feature> Foo {
55
| ^^^^^^^ not a type
66

77
error[E0207]: the const parameter `H` is not constrained by the impl trait, self type, or predicates
8-
--> $DIR/issue-78654.rs:9:12
8+
--> $DIR/issue-78654.rs:9:6
99
|
1010
LL | impl<const H: feature> Foo {
11-
| ^ unconstrained const parameter
11+
| ^^^^^^^^^^^^^^^^ unconstrained const parameter
1212
|
1313
= note: expressions using a const parameter must map each value to a distinct output value
1414
= note: proving the result of expressions other than the parameter are unique is not supported

‎src/test/ui/async-await/issues/issue-78654.min.stderr

+2-2
Original file line numberDiff line numberDiff line change
@@ -5,10 +5,10 @@ LL | impl<const H: feature> Foo {
55
| ^^^^^^^ not a type
66

77
error[E0207]: the const parameter `H` is not constrained by the impl trait, self type, or predicates
8-
--> $DIR/issue-78654.rs:9:12
8+
--> $DIR/issue-78654.rs:9:6
99
|
1010
LL | impl<const H: feature> Foo {
11-
| ^ unconstrained const parameter
11+
| ^^^^^^^^^^^^^^^^ unconstrained const parameter
1212
|
1313
= note: expressions using a const parameter must map each value to a distinct output value
1414
= note: proving the result of expressions other than the parameter are unique is not supported

‎src/test/ui/const-generics/defaults/default-on-impl.stderr

+2-2
Original file line numberDiff line numberDiff line change
@@ -1,8 +1,8 @@
11
error: defaults for const parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
2-
--> $DIR/default-on-impl.rs:3:12
2+
--> $DIR/default-on-impl.rs:3:6
33
|
44
LL | impl<const N: usize = 1> Foo<N> {}
5-
| ^
5+
| ^^^^^^^^^^^^^^^^^^
66

77
error: aborting due to previous error
88

‎src/test/ui/const-generics/generic_const_exprs/issue-76595.stderr

+1-1
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@ note: function defined here, with 2 generic parameters: `T`, `P`
1010
--> $DIR/issue-76595.rs:10:4
1111
|
1212
LL | fn test<T, const P: usize>() where Bool<{core::mem::size_of::<T>() > 4}>: True {
13-
| ^^^^ - -
13+
| ^^^^ - --------------
1414
help: add missing generic argument
1515
|
1616
LL | test::<2, P>();

‎src/test/ui/const-generics/incorrect-number-of-const-args.stderr

+2-2
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@ note: function defined here, with 2 generic parameters: `X`, `Y`
1010
--> $DIR/incorrect-number-of-const-args.rs:1:4
1111
|
1212
LL | fn foo<const X: usize, const Y: usize>() -> usize {
13-
| ^^^ - -
13+
| ^^^ -------------- --------------
1414
help: add missing generic argument
1515
|
1616
LL | foo::<0, Y>();
@@ -28,7 +28,7 @@ note: function defined here, with 2 generic parameters: `X`, `Y`
2828
--> $DIR/incorrect-number-of-const-args.rs:1:4
2929
|
3030
LL | fn foo<const X: usize, const Y: usize>() -> usize {
31-
| ^^^ - -
31+
| ^^^ -------------- --------------
3232

3333
error: aborting due to 2 previous errors
3434

‎src/test/ui/const-generics/issues/issue-68366.full.stderr

+4-4
Original file line numberDiff line numberDiff line change
@@ -1,17 +1,17 @@
11
error[E0207]: the const parameter `N` is not constrained by the impl trait, self type, or predicates
2-
--> $DIR/issue-68366.rs:11:13
2+
--> $DIR/issue-68366.rs:11:7
33
|
44
LL | impl <const N: usize> Collatz<{Some(N)}> {}
5-
| ^ unconstrained const parameter
5+
| ^^^^^^^^^^^^^^ unconstrained const parameter
66
|
77
= note: expressions using a const parameter must map each value to a distinct output value
88
= note: proving the result of expressions other than the parameter are unique is not supported
99

1010
error[E0207]: the const parameter `N` is not constrained by the impl trait, self type, or predicates
11-
--> $DIR/issue-68366.rs:17:12
11+
--> $DIR/issue-68366.rs:17:6
1212
|
1313
LL | impl<const N: usize> Foo {}
14-
| ^ unconstrained const parameter
14+
| ^^^^^^^^^^^^^^ unconstrained const parameter
1515
|
1616
= note: expressions using a const parameter must map each value to a distinct output value
1717
= note: proving the result of expressions other than the parameter are unique is not supported

‎src/test/ui/const-generics/issues/issue-68366.min.stderr

+4-4
Original file line numberDiff line numberDiff line change
@@ -8,19 +8,19 @@ LL | impl <const N: usize> Collatz<{Some(N)}> {}
88
= help: use `#![feature(generic_const_exprs)]` to allow generic const expressions
99

1010
error[E0207]: the const parameter `N` is not constrained by the impl trait, self type, or predicates
11-
--> $DIR/issue-68366.rs:11:13
11+
--> $DIR/issue-68366.rs:11:7
1212
|
1313
LL | impl <const N: usize> Collatz<{Some(N)}> {}
14-
| ^ unconstrained const parameter
14+
| ^^^^^^^^^^^^^^ unconstrained const parameter
1515
|
1616
= note: expressions using a const parameter must map each value to a distinct output value
1717
= note: proving the result of expressions other than the parameter are unique is not supported
1818

1919
error[E0207]: the const parameter `N` is not constrained by the impl trait, self type, or predicates
20-
--> $DIR/issue-68366.rs:17:12
20+
--> $DIR/issue-68366.rs:17:6
2121
|
2222
LL | impl<const N: usize> Foo {}
23-
| ^ unconstrained const parameter
23+
| ^^^^^^^^^^^^^^ unconstrained const parameter
2424
|
2525
= note: expressions using a const parameter must map each value to a distinct output value
2626
= note: proving the result of expressions other than the parameter are unique is not supported

‎src/test/ui/const-generics/issues/issue-86820.stderr

+4-4
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,14 @@
11
error[E0053]: method `bit` has an incompatible const parameter type for trait
2-
--> $DIR/issue-86820.rs:17:18
2+
--> $DIR/issue-86820.rs:17:12
33
|
44
LL | fn bit<const I : usize>(self) -> bool {
5-
| ^
5+
| ^^^^^^^^^^^^^^^
66
|
77
note: the const parameter `I` has type `usize`, but the declaration in trait `Bits::bit` has type `u8`
8-
--> $DIR/issue-86820.rs:12:18
8+
--> $DIR/issue-86820.rs:12:12
99
|
1010
LL | fn bit<const I : u8>(self) -> bool;
11-
| ^
11+
| ^^^^^^^^^^^^
1212

1313
error: aborting due to previous error
1414

‎src/test/ui/const-generics/min_const_generics/default_function_param.stderr

+2-2
Original file line numberDiff line numberDiff line change
@@ -1,8 +1,8 @@
11
error: defaults for const parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
2-
--> $DIR/default_function_param.rs:3:14
2+
--> $DIR/default_function_param.rs:3:8
33
|
44
LL | fn foo<const SIZE: usize = 5usize>() {}
5-
| ^^^^
5+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
66

77
error: aborting due to previous error
88

‎src/test/ui/const-generics/parser-error-recovery/issue-89013-no-kw.stderr

+1-1
Original file line numberDiff line numberDiff line change
@@ -17,7 +17,7 @@ note: trait defined here, with 1 generic parameter: `N`
1717
--> $DIR/issue-89013-no-kw.rs:1:7
1818
|
1919
LL | trait Foo<const N: usize> {
20-
| ^^^ -
20+
| ^^^ --------------
2121
help: add missing generic argument
2222
|
2323
LL | impl Foo<N, N = 3> for Bar {

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