From 0f4255ece2e2ff5e0ab7467513cd45d3cdecb27d Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Wed, 8 Mar 2023 00:00:02 +0000
Subject: [PATCH] Dedup copy field errors for identical types

---
 compiler/rustc_hir_analysis/src/coherence/builtin.rs      | 8 ++++++++
 .../missing-bound-in-derive-copy-impl-3.stderr            | 4 ----
 .../suggestions/missing-bound-in-derive-copy-impl.stderr  | 4 ----
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/compiler/rustc_hir_analysis/src/coherence/builtin.rs b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
index 852c5768399..8294d92c936 100644
--- a/compiler/rustc_hir_analysis/src/coherence/builtin.rs
+++ b/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`");
 
diff --git a/tests/ui/suggestions/missing-bound-in-derive-copy-impl-3.stderr b/tests/ui/suggestions/missing-bound-in-derive-copy-impl-3.stderr
index 83bc65ea1c8..09696e0613e 100644
--- a/tests/ui/suggestions/missing-bound-in-derive-copy-impl-3.stderr
+++ b/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
    |
diff --git a/tests/ui/suggestions/missing-bound-in-derive-copy-impl.stderr b/tests/ui/suggestions/missing-bound-in-derive-copy-impl.stderr
index 65dc3113731..8585fe47bf3 100644
--- a/tests/ui/suggestions/missing-bound-in-derive-copy-impl.stderr
+++ b/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`
    |