Only label place where type is needed if span is meaningful

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -313,11 +313,12 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     pub fn emit_inference_failure_err(
         &self,
         body_id: Option<hir::BodyId>,
-        span: Span,
+        failure_span: Span,
         arg: GenericArg<'tcx>,
         // FIXME(#94483): Either use this or remove it.
         _impl_candidates: Vec<ty::TraitRef<'tcx>>,
         error_code: TypeAnnotationNeeded,
+        should_label_span: bool,
     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
         let arg = self.resolve_vars_if_possible(arg);
         let arg_data = self.extract_inference_diagnostics_data(arg, None);
@@ -326,7 +327,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             // If we don't have any typeck results we're outside
             // of a body, so we won't be able to get better info
             // here.
-            return self.bad_inference_failure_err(span, arg_data, error_code);
+            return self.bad_inference_failure_err(failure_span, arg_data, error_code);
         };
         let typeck_results = typeck_results.borrow();
         let typeck_results = &typeck_results;
@@ -338,7 +339,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
 
         let Some(InferSource { span, kind }) = local_visitor.infer_source else {
-            return self.bad_inference_failure_err(span, arg_data, error_code)
+            return self.bad_inference_failure_err(failure_span, arg_data, error_code)
         };
 
         let error_code = error_code.into();
@@ -347,6 +348,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             &format!("type annotations needed{}", kind.ty_msg(self)),
             error_code,
         );
+
+        if should_label_span && !failure_span.overlaps(span) {
+            err.span_label(failure_span, "type must be known at this point");
+        }
+
         match kind {
             InferSourceKind::LetBinding { insert_span, pattern_name, ty } => {
                 let suggestion_msg = if let Some(name) = pattern_name {

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

@@ -2002,6 +2002,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                             subst,
                             vec![],
                             ErrorCode::E0282,
+                            false,
                         )
                         .emit();
                     }
@@ -2019,6 +2020,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                     subst,
                     impl_candidates,
                     ErrorCode::E0283,
+                    false,
                 );
 
                 let obligation = Obligation::new(
@@ -2110,7 +2112,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                     return;
                 }
 
-                self.emit_inference_failure_err(body_id, span, arg, vec![], ErrorCode::E0282)
+                self.emit_inference_failure_err(body_id, span, arg, vec![], ErrorCode::E0282, false)
             }
 
             ty::PredicateKind::Subtype(data) => {
@@ -2124,7 +2126,14 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                 let SubtypePredicate { a_is_expected: _, a, b } = data;
                 // both must be type variables, or the other would've been instantiated
                 assert!(a.is_ty_var() && b.is_ty_var());
-                self.emit_inference_failure_err(body_id, span, a.into(), vec![], ErrorCode::E0282)
+                self.emit_inference_failure_err(
+                    body_id,
+                    span,
+                    a.into(),
+                    vec![],
+                    ErrorCode::E0282,
+                    false,
+                )
             }
             ty::PredicateKind::Projection(data) => {
                 let self_ty = data.projection_ty.self_ty();
@@ -2140,6 +2149,7 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                         self_ty.into(),
                         vec![],
                         ErrorCode::E0284,
+                        false,
                     );
                     err.note(&format!("cannot satisfy `{}`", predicate));
                     err

compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs

@@ -1538,9 +1538,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ty
         } else {
             if !self.is_tainted_by_errors() {
-                self.emit_inference_failure_err((**self).body_id, sp, ty.into(), vec![], E0282)
-                    .note("type must be known at this point")
-                    .emit();
+                self.emit_inference_failure_err(
+                    (**self).body_id,
+                    sp,
+                    ty.into(),
+                    vec![],
+                    E0282,
+                    true,
+                )
+                .emit();
             }
             let err = self.tcx.ty_error();
             self.demand_suptype(sp, err, ty);

compiler/rustc_typeck/src/check/writeback.rs

@@ -694,6 +694,7 @@ impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
                     t.into(),
                     vec![],
                     E0282,
+                    false,
                 )
                 .emit();
         }
@@ -708,6 +709,7 @@ impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
                     c.into(),
                     vec![],
                     E0282,
+                    false,
                 )
                 .emit();
         }