Remove some fields from ObligationCauseCode

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

@@ -6,7 +6,6 @@ use rustc_errors::{struct_span_err, DiagnosticBuilder};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::TyCtxt;
-use rustc_span::symbol::Symbol;
 use rustc_span::{MultiSpan, Span};
 use std::fmt;
 use std::iter;
@@ -15,8 +14,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     pub fn report_extra_impl_obligation(
         &self,
         error_span: Span,
-        item_name: Symbol,
-        _impl_item_def_id: DefId,
+        impl_item_def_id: DefId,
         trait_item_def_id: DefId,
         requirement: &dyn fmt::Display,
     ) -> DiagnosticBuilder<'tcx> {
@@ -27,6 +25,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
 
         if let Some(trait_item_span) = self.tcx.hir().span_if_local(trait_item_def_id) {
             let span = self.tcx.sess.source_map().guess_head_span(trait_item_span);
+            let item_name = self.tcx.item_name(impl_item_def_id);
             err.span_label(span, format!("definition of `{}` from trait", item_name));
         }