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

Author: bors

compiler/rustc_ast_lowering/src/lib.rs

@@ -2068,7 +2068,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         hir::GenericParam {
             hir_id,
             name,
-            span: self.lower_span(param.ident.span),
+            span: self.lower_span(param.span()),
             pure_wrt_drop: self.sess.contains_name(&param.attrs, sym::may_dangle),
             bounds: self.arena.alloc_from_iter(bounds),
             kind,

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -772,14 +772,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             Some((issued_span, span)),
         );
 
-        self.suggest_using_local_if_applicable(
-            &mut err,
-            location,
-            (place, span),
-            gen_borrow_kind,
-            issued_borrow,
-            explanation,
-        );
+        self.suggest_using_local_if_applicable(&mut err, location, issued_borrow, explanation);
 
         err
     }
@@ -789,8 +782,6 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         &self,
         err: &mut Diagnostic,
         location: Location,
-        (place, span): (Place<'tcx>, Span),
-        gen_borrow_kind: BorrowKind,
         issued_borrow: &BorrowData<'tcx>,
         explanation: BorrowExplanation,
     ) {
@@ -822,7 +813,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             return;
         };
         let inner_param_uses = find_all_local_uses::find(self.body, inner_param.local);
-        let Some((inner_call_loc,inner_call_term)) = inner_param_uses.into_iter().find_map(|loc| {
+        let Some((inner_call_loc, inner_call_term)) = inner_param_uses.into_iter().find_map(|loc| {
             let Either::Right(term) = self.body.stmt_at(loc) else {
                 debug!("{:?} is a statement, so it can't be a call", loc);
                 return None;
@@ -833,7 +824,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             };
             debug!("checking call args for uses of inner_param: {:?}", args);
             if args.contains(&Operand::Move(inner_param)) {
-                Some((loc,term))
+                Some((loc, term))
             } else {
                 None
             }

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

@@ -540,6 +540,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         );
                         self.note_version_mismatch(&mut err, &trait_ref);
                         self.suggest_remove_await(&obligation, &mut err);
+                        self.suggest_derive(&obligation, &mut err, trait_predicate);
 
                         if Some(trait_ref.def_id()) == tcx.lang_items().try_trait() {
                             self.suggest_await_before_try(

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

@@ -189,6 +189,13 @@ pub trait InferCtxtExt<'tcx> {
         err: &mut Diagnostic,
         trait_ref: &ty::PolyTraitRef<'tcx>,
     );
+
+    fn suggest_derive(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+        err: &mut Diagnostic,
+        trait_pred: ty::PolyTraitPredicate<'tcx>,
+    );
 }
 
 fn predicate_constraint(generics: &hir::Generics<'_>, pred: String) -> (Span, String) {
@@ -2651,6 +2658,68 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             _ => {}
         }
     }
+
+    fn suggest_derive(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+        err: &mut Diagnostic,
+        trait_pred: ty::PolyTraitPredicate<'tcx>,
+    ) {
+        let Some(diagnostic_name) = self.tcx.get_diagnostic_name(trait_pred.def_id()) else {
+            return;
+        };
+        let (adt, substs) = match trait_pred.skip_binder().self_ty().kind() {
+            ty::Adt(adt, substs) if adt.did().is_local() => (adt, substs),
+            _ => return,
+        };
+        let can_derive = {
+            let is_derivable_trait = match diagnostic_name {
+                sym::Default => !adt.is_enum(),
+                sym::PartialEq | sym::PartialOrd => {
+                    let rhs_ty = trait_pred.skip_binder().trait_ref.substs.type_at(1);
+                    trait_pred.skip_binder().self_ty() == rhs_ty
+                }
+                sym::Eq | sym::Ord | sym::Clone | sym::Copy | sym::Hash | sym::Debug => true,
+                _ => false,
+            };
+            is_derivable_trait &&
+                // Ensure all fields impl the trait.
+                adt.all_fields().all(|field| {
+                    let field_ty = field.ty(self.tcx, substs);
+                    let trait_substs = match diagnostic_name {
+                        sym::PartialEq | sym::PartialOrd => {
+                            self.tcx.mk_substs_trait(field_ty, &[field_ty.into()])
+                        }
+                        _ => self.tcx.mk_substs_trait(field_ty, &[]),
+                    };
+                    let trait_pred = trait_pred.map_bound_ref(|tr| ty::TraitPredicate {
+                        trait_ref: ty::TraitRef {
+                            substs: trait_substs,
+                            ..trait_pred.skip_binder().trait_ref
+                        },
+                        ..*tr
+                    });
+                    let field_obl = Obligation::new(
+                        obligation.cause.clone(),
+                        obligation.param_env,
+                        trait_pred.to_predicate(self.tcx),
+                    );
+                    self.predicate_must_hold_modulo_regions(&field_obl)
+                })
+        };
+        if can_derive {
+            err.span_suggestion_verbose(
+                self.tcx.def_span(adt.did()).shrink_to_lo(),
+                &format!(
+                    "consider annotating `{}` with `#[derive({})]`",
+                    trait_pred.skip_binder().self_ty(),
+                    diagnostic_name.to_string(),
+                ),
+                format!("#[derive({})]\n", diagnostic_name.to_string()),
+                Applicability::MaybeIncorrect,
+            );
+        }
+    }
 }
 
 /// Collect all the returned expressions within the input expression.

library/core/src/macros/panic.md

@@ -1,8 +1,7 @@
 Panics the current thread.
 
 This allows a program to terminate immediately and provide feedback
-to the caller of the program. `panic!` should be used when a program reaches
-an unrecoverable state.
+to the caller of the program.
 
 This macro is the perfect way to assert conditions in example code and in
 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`,
 which contains either a `&str` or `String` for regular `panic!()` invocations.
 To panic with a value of another other type, [`panic_any`] can be used.
 
-[`Result`] enum is often a better solution for recovering from errors than
-using the `panic!` macro. This macro should be used to avoid proceeding using
-incorrect values, such as from external sources. Detailed information about
-error handling is found in the [book].
-
 See also the macro [`compile_error!`], for raising errors during compilation.
 
+# When to use `panic!` vs `Result`
+
+The Rust model of error handling groups errors into two major categories:
+recoverable and unrecoverable errors. For a recoverable error, such as a file
+not found error, it’s reasonable to report the problem to the user and retry
+the operation. Unrecoverable errors are always symptoms of bugs, like trying to
+access a location beyond the end of an array.
+
+The Rust language and standard library provides `Result` and `panic!` as parts
+of two complementary systems for representing, reporting, propagating, reacting
+to, and discarding errors for in these two categories.
+
+The `panic!` macro is provided to represent unrecoverable errors, whereas the
+`Result` enum is provided to represent recoverable errors. For more detailed
+information about error handling check out the [book] or the [`std::result`]
+module docs.
+
 [ounwrap]: Option::unwrap
 [runwrap]: Result::unwrap
 [`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.
 [`Any`]: crate::any::Any
 [`format!`]: ../std/macro.format.html
 [book]: ../book/ch09-00-error-handling.html
+[`std::result`]: ../std/result/index.html
 
 # Current implementation
 

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

@@ -5,6 +5,10 @@ LL |     let headers = [Header{value: &[]}; 128];
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `Header<'_>`
    |
    = note: the `Copy` trait is required because the repeated element will be copied
+help: consider annotating `Header<'_>` with `#[derive(Copy)]`
+   |
+LL | #[derive(Copy)]
+   |
 
 error[E0277]: the trait bound `Header<'_>: Copy` is not satisfied
   --> $DIR/repeat_empty_ok.rs:13:19
@@ -13,6 +17,10 @@ LL |     let headers = [Header{value: &[0]}; 128];
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `Header<'_>`
    |
    = note: the `Copy` trait is required because the repeated element will be copied
+help: consider annotating `Header<'_>` with `#[derive(Copy)]`
+   |
+LL | #[derive(Copy)]
+   |
 
 error: aborting due to 2 previous errors
 

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

@@ -9,6 +9,10 @@ note: required by a bound in `Tr::Ty`
    |
 LL |     type Ty: Clone = NotClone;
    |              ^^^^^ required by this bound in `Tr::Ty`
+help: consider annotating `NotClone` with `#[derive(Clone)]`
+   |
+LL | #[derive(Clone)]
+   |
 
 error[E0277]: the trait bound `NotClone: Clone` is not satisfied
   --> $DIR/defaults-suitability.rs:22:15
@@ -24,6 +28,10 @@ LL |     Self::Ty: Clone,
 LL | {
 LL |     type Ty = NotClone;
    |          -- required by a bound in this
+help: consider annotating `NotClone` with `#[derive(Clone)]`
+   |
+LL | #[derive(Clone)]
+   |
 
 error[E0277]: the trait bound `T: Clone` is not satisfied
   --> $DIR/defaults-suitability.rs:28:23

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

@@ -8,7 +8,7 @@ note: required by a bound in `Add`
   --> $SRC_DIR/core/src/ops/arith.rs:LL:COL
    |
 LL | pub trait Add<Rhs = Self> {
-   |               ^^^ required by this bound in `Add`
+   |               ^^^^^^^^^^ required by this bound in `Add`
 help: consider further restricting `Self`
    |
 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

@@ -5,10 +5,10 @@ LL | impl<const H: feature> Foo {
    |               ^^^^^^^ not a type
 
 error[E0207]: the const parameter `H` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/issue-78654.rs:9:12
+  --> $DIR/issue-78654.rs:9:6
    |
 LL | impl<const H: feature> Foo {
-   |            ^ unconstrained const parameter
+   |      ^^^^^^^^^^^^^^^^ unconstrained const parameter
    |
    = note: expressions using a const parameter must map each value to a distinct output value
    = 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

@@ -5,10 +5,10 @@ LL | impl<const H: feature> Foo {
    |               ^^^^^^^ not a type
 
 error[E0207]: the const parameter `H` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/issue-78654.rs:9:12
+  --> $DIR/issue-78654.rs:9:6
    |
 LL | impl<const H: feature> Foo {
-   |            ^ unconstrained const parameter
+   |      ^^^^^^^^^^^^^^^^ unconstrained const parameter
    |
    = note: expressions using a const parameter must map each value to a distinct output value
    = note: proving the result of expressions other than the parameter are unique is not supported