Rollup merge of rust-lang#95525 - ohno418:suggest-derivable-trait-E0277, r=compiler-errors

Suggest derivable trait on E0277 error

Closes rust-lang#95099 .

Author: Dylan-DPC

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) {
@@ -2650,6 +2657,68 @@ 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.

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/derives/derives-span-Clone-enum-struct-variant.stderr

@@ -8,6 +8,10 @@ LL |      x: Error
    |      ^^^^^^^^ the trait `Clone` is not implemented for `Error`
    |
    = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(Clone)]`
+   |
+LL | #[derive(Clone)]
+   |
 
 error: aborting due to previous error
 

src/test/ui/derives/derives-span-Clone-enum.stderr

@@ -8,6 +8,10 @@ LL |      Error
    |      ^^^^^ the trait `Clone` is not implemented for `Error`
    |
    = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(Clone)]`
+   |
+LL | #[derive(Clone)]
+   |
 
 error: aborting due to previous error
 

src/test/ui/derives/derives-span-Clone-struct.stderr

@@ -8,6 +8,10 @@ LL |     x: Error
    |     ^^^^^^^^ the trait `Clone` is not implemented for `Error`
    |
    = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(Clone)]`
+   |
+LL | #[derive(Clone)]
+   |
 
 error: aborting due to previous error
 

src/test/ui/derives/derives-span-Clone-tuple-struct.stderr

@@ -8,6 +8,10 @@ LL |     Error
    |     ^^^^^ the trait `Clone` is not implemented for `Error`
    |
    = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(Clone)]`
+   |
+LL | #[derive(Clone)]
+   |
 
 error: aborting due to previous error
 

src/test/ui/derives/derives-span-Debug-enum-struct-variant.stderr

@@ -10,6 +10,10 @@ LL |      x: Error
    = help: the trait `Debug` is not implemented for `Error`
    = note: add `#[derive(Debug)]` to `Error` or manually `impl Debug for Error`
    = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(Debug)]`
+   |
+LL | #[derive(Debug)]
+   |
 
 error: aborting due to previous error
 

src/test/ui/derives/derives-span-Debug-enum.stderr

@@ -10,6 +10,10 @@ LL |      Error
    = help: the trait `Debug` is not implemented for `Error`
    = note: add `#[derive(Debug)]` to `Error` or manually `impl Debug for Error`
    = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(Debug)]`
+   |
+LL | #[derive(Debug)]
+   |
 
 error: aborting due to previous error