Rollup merge of rust-lang#113945 - chenyukang:yukang-fix-113447-slice-2, r=cjgillot

Fix wrong span for trait selection failure error reporting

Fixes rust-lang#113447

Author: matthiaskrgr

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(

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;
         };
 

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]`
+}

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]`
+}

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`.