No need to make a new fulfillment context

Author: Nadrieril

compiler/rustc_hir_typeck/src/pat.rs

@@ -20,10 +20,7 @@ use rustc_span::source_map::Spanned;
 use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::{BytePos, Span, DUMMY_SP};
 use rustc_target::abi::FieldIdx;
-use rustc_trait_selection::traits::{
-    error_reporting::TypeErrCtxtExt, ObligationCause, Pattern, StructurallyNormalizeExt,
-    TraitEngine, TraitEngineExt,
-};
+use rustc_trait_selection::traits::{ObligationCause, Pattern};
 use ty::VariantDef;
 
 use std::cmp;
@@ -1987,22 +1984,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             tcx.require_lang_item(hir::LangItem::DerefTarget, Some(span)),
             [expected],
         );
-
-        let mut fulfill_cx = <dyn TraitEngine<'_>>::new(&self.infcx);
-        let cause = self.pattern_cause(pat_info.top_info, span);
-        let normalized_ty = match self
-            .infcx
-            .at(&cause, self.param_env)
-            .structurally_normalize(ty, &mut *fulfill_cx)
-        {
-            Ok(normalized_ty) => normalized_ty,
-            Err(errors) => {
-                let reported = self.infcx.err_ctxt().report_fulfillment_errors(errors);
-                return Ty::new_error(tcx, reported);
-            }
-        };
-
-        let ty = self.resolve_vars_if_possible(normalized_ty);
+        let ty = self.normalize(span, ty);
+        let ty = self.try_structurally_resolve_type(span, ty);
+        let ty = self.resolve_vars_if_possible(ty);
         self.check_pat(inner, ty, pat_info);
         expected
     }