Add require_type_is_sized_deferred.

src/librustc_typeck/check/mod.rs

@@ -208,6 +208,10 @@ pub struct Inherited<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 
     fulfillment_cx: RefCell<Box<dyn TraitEngine<'tcx>>>,
 
+    // Some additional `Sized` obligations badly affect type inference.
+    // These obligations are added in a later stage of typeck.
+    deferred_sized_obligations: RefCell<Vec<(Ty<'tcx>, Span, traits::ObligationCauseCode<'tcx>)>>,
+
     // When we process a call like `c()` where `c` is a closure type,
     // we may not have decided yet whether `c` is a `Fn`, `FnMut`, or
     // `FnOnce` closure. In that case, we defer full resolution of the
@@ -644,6 +648,7 @@ impl<'a, 'gcx, 'tcx> Inherited<'a, 'gcx, 'tcx> {
             infcx,
             fulfillment_cx: RefCell::new(TraitEngine::new(tcx)),
             locals: RefCell::new(Default::default()),
+            deferred_sized_obligations: RefCell::new(Vec::new()),
             deferred_call_resolutions: RefCell::new(Default::default()),
             deferred_cast_checks: RefCell::new(Vec::new()),
             deferred_generator_interiors: RefCell::new(Vec::new()),
@@ -907,6 +912,10 @@ fn typeck_tables_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         fcx.closure_analyze(body);
         assert!(fcx.deferred_call_resolutions.borrow().is_empty());
         fcx.resolve_generator_interiors(def_id);
+
+        for (ty, span, code) in fcx.deferred_sized_obligations.borrow_mut().drain(..) {
+            fcx.require_type_is_sized(ty, span, code);
+        }
         fcx.select_all_obligations_or_error();
 
         if fn_decl.is_some() {
@@ -2345,6 +2354,14 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         self.require_type_meets(ty, span, code, lang_item);
     }
 
+    pub fn require_type_is_sized_deferred(&self,
+                                          ty: Ty<'tcx>,
+                                          span: Span,
+                                          code: traits::ObligationCauseCode<'tcx>)
+    {
+        self.deferred_sized_obligations.borrow_mut().push((ty, span, code));
+    }
+
     pub fn register_bound(&self,
                           ty: Ty<'tcx>,
                           def_id: DefId,