From 3635b48973ee17951c81769e4a62b0a4891a2501 Mon Sep 17 00:00:00 2001
From: yukang <moorekang@gmail.com>
Date: Sat, 22 Jul 2023 10:13:49 +0800
Subject: [PATCH 1/2] Fix wrong span for trait selection failure error
 reporting

---
 .../src/traits/error_reporting/mod.rs         |  8 ++++++
 tests/ui/dst/issue-113447.fixed               | 25 +++++++++++++++++++
 tests/ui/dst/issue-113447.rs                  | 25 +++++++++++++++++++
 tests/ui/dst/issue-113447.stderr              | 25 +++++++++++++++++++
 4 files changed, 83 insertions(+)
 create mode 100644 tests/ui/dst/issue-113447.fixed
 create mode 100644 tests/ui/dst/issue-113447.rs
 create mode 100644 tests/ui/dst/issue-113447.stderr

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index eae13eb630290..4d85e2b60893e 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -2987,6 +2987,14 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         unsatisfied_const: bool,
     ) {
         let body_def_id = obligation.cause.body_id;
+        let span = if let ObligationCauseCode::BinOp { rhs_span: Some(rhs_span), .. } =
+            obligation.cause.code()
+        {
+            *rhs_span
+        } else {
+            span
+        };
+
         // Try to report a help message
         if is_fn_trait
             && let Ok((implemented_kind, params)) = self.type_implements_fn_trait(
diff --git a/tests/ui/dst/issue-113447.fixed b/tests/ui/dst/issue-113447.fixed
new file mode 100644
index 0000000000000..536f680f697c7
--- /dev/null
+++ b/tests/ui/dst/issue-113447.fixed
@@ -0,0 +1,25 @@
+// run-rustfix
+
+pub struct Bytes;
+
+impl Bytes {
+    pub fn as_slice(&self) -> &[u8] {
+        todo!()
+    }
+}
+
+impl PartialEq<[u8]> for Bytes {
+    fn eq(&self, other: &[u8]) -> bool {
+        self.as_slice() == other
+    }
+}
+
+impl PartialEq<Bytes> for &[u8] {
+    fn eq(&self, other: &Bytes) -> bool {
+        *other == **self
+    }
+}
+
+fn main() {
+    let _ = &[0u8] == &[0xAA][..]; //~ ERROR can't compare `&[u8; 1]` with `[{integer}; 1]`
+}
diff --git a/tests/ui/dst/issue-113447.rs b/tests/ui/dst/issue-113447.rs
new file mode 100644
index 0000000000000..c10a4f2ff8ec4
--- /dev/null
+++ b/tests/ui/dst/issue-113447.rs
@@ -0,0 +1,25 @@
+// run-rustfix
+
+pub struct Bytes;
+
+impl Bytes {
+    pub fn as_slice(&self) -> &[u8] {
+        todo!()
+    }
+}
+
+impl PartialEq<[u8]> for Bytes {
+    fn eq(&self, other: &[u8]) -> bool {
+        self.as_slice() == other
+    }
+}
+
+impl PartialEq<Bytes> for &[u8] {
+    fn eq(&self, other: &Bytes) -> bool {
+        *other == **self
+    }
+}
+
+fn main() {
+    let _ = &[0u8] == [0xAA]; //~ ERROR can't compare `&[u8; 1]` with `[{integer}; 1]`
+}
diff --git a/tests/ui/dst/issue-113447.stderr b/tests/ui/dst/issue-113447.stderr
new file mode 100644
index 0000000000000..240553a675bfe
--- /dev/null
+++ b/tests/ui/dst/issue-113447.stderr
@@ -0,0 +1,25 @@
+error[E0277]: can't compare `&[u8; 1]` with `[{integer}; 1]`
+  --> $DIR/issue-113447.rs:24:20
+   |
+LL |     let _ = &[0u8] == [0xAA];
+   |                    ^^ no implementation for `&[u8; 1] == [{integer}; 1]`
+   |
+   = help: the trait `PartialEq<[{integer}; 1]>` is not implemented for `&[u8; 1]`
+   = help: the following other types implement trait `PartialEq<Rhs>`:
+             <[A; N] as PartialEq<[B; N]>>
+             <[A; N] as PartialEq<[B]>>
+             <[A; N] as PartialEq<&[B]>>
+             <[A; N] as PartialEq<&mut [B]>>
+             <[T] as PartialEq<Vec<U, A>>>
+             <[A] as PartialEq<[B]>>
+             <[B] as PartialEq<[A; N]>>
+             <&[u8] as PartialEq<Bytes>>
+           and 4 others
+help: convert the array to a `&[u8]` slice instead
+   |
+LL |     let _ = &[0u8] == &[0xAA][..];
+   |                       +      ++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

From cde8f06503d06d254aa4191438588ba9b2a36b77 Mon Sep 17 00:00:00 2001
From: yukang <moorekang@gmail.com>
Date: Fri, 4 Aug 2023 00:14:13 +0800
Subject: [PATCH 2/2] enable suggest convert to slice for binary operation

---
 .../src/traits/error_reporting/suggestions.rs             | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 46c31c77613ef..bde72c691dc99 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -3953,9 +3953,11 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         candidate_impls: &[ImplCandidate<'tcx>],
         span: Span,
     ) {
-        // We can only suggest the slice coersion for function arguments since the suggestion
-        // would make no sense in turbofish or call
-        let ObligationCauseCode::FunctionArgumentObligation { .. } = obligation.cause.code() else {
+        // We can only suggest the slice coersion for function and binary operation arguments,
+        // since the suggestion would make no sense in turbofish or call
+        let (ObligationCauseCode::BinOp { .. }
+        | ObligationCauseCode::FunctionArgumentObligation { .. }) = obligation.cause.code()
+        else {
             return;
         };