Suggest derivable trait on E0277

Author: ohno418

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

@@ -536,6 +536,7 @@ 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(&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 +189,8 @@ pub trait InferCtxtExt<'tcx> {
         err: &mut Diagnostic,
         trait_ref: &ty::PolyTraitRef<'tcx>,
     );
+
+    fn suggest_derive(&self, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>);
 }
 
 fn predicate_constraint(generics: &hir::Generics<'_>, pred: String) -> (Span, String) {
@@ -2589,6 +2591,39 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             _ => {}
         }
     }
+
+    fn suggest_derive(&self, err: &mut Diagnostic, trait_pred: ty::PolyTraitPredicate<'tcx>) {
+        if let Some(diagnostic_name) = self.tcx.get_diagnostic_name(trait_pred.def_id()) {
+            let adt = match trait_pred.skip_binder().self_ty().ty_adt_def() {
+                Some(adt) if adt.did().is_local() => adt,
+                _ => return,
+            };
+            let can_derive = match diagnostic_name {
+                sym::Default => !adt.is_enum(),
+                sym::Eq
+                | sym::PartialEq
+                | sym::Ord
+                | sym::PartialOrd
+                | sym::Clone
+                | sym::Copy
+                | sym::Hash
+                | sym::Debug => true,
+                _ => false,
+            };
+            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().to_string(),
+                        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/consts/const-blocks/trait-error.stderr

@@ -7,6 +7,10 @@ LL |     [Foo(String::new()); 4];
    = help: the following implementations were found:
              <Foo<T> as Copy>
    = note: the `Copy` trait is required because the repeated element will be copied
+help: consider annotating `Foo<String>` with `#[derive(Copy)]`
+   |
+LL | #[derive(Copy)]
+   |
 
 error: aborting due to previous error
 

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
 

src/test/ui/derives/derives-span-Debug-struct.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-tuple-struct.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
 

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

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

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

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

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

@@ -13,6 +13,10 @@ note: required by a bound in `AssertParamIsEq`
 LL | pub struct AssertParamIsEq<T: Eq + ?Sized> {
    |                               ^^ required by this bound in `AssertParamIsEq`
    = note: this error originates in the derive macro `Eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(Eq)]`
+   |
+LL | #[derive(Eq)]
+   |
 
 error: aborting due to previous error
 

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

@@ -13,6 +13,10 @@ note: required by a bound in `AssertParamIsEq`
 LL | pub struct AssertParamIsEq<T: Eq + ?Sized> {
    |                               ^^ required by this bound in `AssertParamIsEq`
    = note: this error originates in the derive macro `Eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(Eq)]`
+   |
+LL | #[derive(Eq)]
+   |
 
 error: aborting due to previous error
 

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

@@ -13,6 +13,10 @@ note: required by a bound in `AssertParamIsEq`
 LL | pub struct AssertParamIsEq<T: Eq + ?Sized> {
    |                               ^^ required by this bound in `AssertParamIsEq`
    = note: this error originates in the derive macro `Eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(Eq)]`
+   |
+LL | #[derive(Eq)]
+   |
 
 error: aborting due to previous error
 

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

@@ -13,6 +13,10 @@ note: required by a bound in `AssertParamIsEq`
 LL | pub struct AssertParamIsEq<T: Eq + ?Sized> {
    |                               ^^ required by this bound in `AssertParamIsEq`
    = note: this error originates in the derive macro `Eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(Eq)]`
+   |
+LL | #[derive(Eq)]
+   |
 
 error: aborting due to previous error
 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

@@ -9,6 +9,10 @@ LL |      x: Error
    |
    = help: the trait `PartialOrd` is not implemented for `Error`
    = note: this error originates in the derive macro `PartialOrd` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(PartialOrd)]`
+   |
+LL | #[derive(PartialOrd)]
+   |
 
 error: aborting due to previous error
 

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

@@ -9,6 +9,10 @@ LL |      Error
    |
    = help: the trait `PartialOrd` is not implemented for `Error`
    = note: this error originates in the derive macro `PartialOrd` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(PartialOrd)]`
+   |
+LL | #[derive(PartialOrd)]
+   |
 
 error: aborting due to previous error
 

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

@@ -9,6 +9,10 @@ LL |     x: Error
    |
    = help: the trait `PartialOrd` is not implemented for `Error`
    = note: this error originates in the derive macro `PartialOrd` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(PartialOrd)]`
+   |
+LL | #[derive(PartialOrd)]
+   |
 
 error: aborting due to previous error
 

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

@@ -9,6 +9,10 @@ LL |     Error
    |
    = help: the trait `PartialOrd` is not implemented for `Error`
    = note: this error originates in the derive macro `PartialOrd` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider annotating `Error` with `#[derive(PartialOrd)]`
+   |
+LL | #[derive(PartialOrd)]
+   |
 
 error: aborting due to previous error