Dedup copy field errors for identical types

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -2,6 +2,7 @@
 //! up data structures required by type-checking/codegen.
 
 use crate::errors::{CopyImplOnNonAdt, CopyImplOnTypeWithDtor, DropImplOnWrongItem};
+use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::{struct_span_err, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
@@ -94,7 +95,14 @@ fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: LocalDefId) {
             let mut errors: BTreeMap<_, Vec<_>> = Default::default();
             let mut bounds = vec![];
 
+            let mut seen_tys = FxHashSet::default();
+
             for (field, ty, reason) in fields {
+                // Only report an error once per type.
+                if !seen_tys.insert(ty) {
+                    continue;
+                }
+
                 let field_span = tcx.def_span(field.did);
                 err.span_label(field_span, "this field does not implement `Copy`");
 

tests/ui/suggestions/missing-bound-in-derive-copy-impl-3.stderr

@@ -6,16 +6,12 @@ LL | #[derive(Debug, Copy, Clone)]
 LL | pub struct AABB<K: Copy>{
 LL |     pub loc: Vector2<K>,
    |     ------------------- this field does not implement `Copy`
-LL |     pub size: Vector2<K>
-   |     -------------------- this field does not implement `Copy`
    |
 note: the `Copy` impl for `Vector2<K>` requires that `K: Debug`
   --> $DIR/missing-bound-in-derive-copy-impl-3.rs:12:14
    |
 LL |     pub loc: Vector2<K>,
    |              ^^^^^^^^^^
-LL |     pub size: Vector2<K>
-   |               ^^^^^^^^^^
    = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider further restricting this bound
    |

tests/ui/suggestions/missing-bound-in-derive-copy-impl.stderr

@@ -6,16 +6,12 @@ LL | #[derive(Debug, Copy, Clone)]
 LL | pub struct AABB<K>{
 LL |     pub loc: Vector2<K>,
    |     ------------------- this field does not implement `Copy`
-LL |     pub size: Vector2<K>
-   |     -------------------- this field does not implement `Copy`
    |
 note: the `Copy` impl for `Vector2<K>` requires that `K: Debug`
   --> $DIR/missing-bound-in-derive-copy-impl.rs:11:14
    |
 LL |     pub loc: Vector2<K>,
    |              ^^^^^^^^^^
-LL |     pub size: Vector2<K>
-   |               ^^^^^^^^^^
    = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider restricting type parameter `K`
    |