More specific error when calling bottom

src/librustc_typeck/check/callee.rs

@@ -113,8 +113,17 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                adjusted_ty,
                autoderefs);
 
+        let ty = self.resolve_type_vars_with_obligations(adjusted_ty);
+        if ty.is_ty_var() {
+            if !self.is_tainted_by_errors() {
+                self.tcx.sess.span_err(callee_expr.span,
+                                       "cannot determine the type of this callee");
+            }
+            return None;
+        }
+
         // If the callee is a bare function or a closure, then we're all set.
-        match self.structurally_resolved_type(callee_expr.span, adjusted_ty).sty {
+        match ty.sty {
             ty::TyFnDef(..) | ty::TyFnPtr(_) => {
                 self.write_autoderef_adjustment(callee_expr.id, autoderefs);
                 return Some(CallStep::Builtin);

src/test/compile-fail/issue-15965.rs

@@ -9,9 +9,6 @@
 // except according to those terms.
 
 fn main() {
-    return
-        { return () }
-//~^ ERROR the type of this value must be known in this context
-    ()
-    ;
+    (return) //~ ERROR cannot determine the type of this callee
+    ();
 }

src/test/compile-fail/issue-18532.rs

@@ -15,6 +15,6 @@
 #![feature(unboxed_closures)]
 
 fn main() {
-    (return)((),());
-    //~^ ERROR the type of this value must be known
+    (return) //~ ERROR cannot determine the type of this callee
+    ((), ());
 }

src/test/compile-fail/unboxed-closures-failed-recursive-fn-2.rs

@@ -24,7 +24,7 @@ fn a() {
                 match closure0.take() {
                     Some(c) => {
                         return c();
-                        //~^ ERROR the type of this value must be known in this context
+                        //~^ ERROR cannot determine the type of this callee
                     }
                     None => { }
                 }