Fix bug when using generic args for unknown functions

Author: varkor

src/librustc_typeck/collect.rs

@@ -1194,6 +1194,7 @@ fn type_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                 }
                                 bug!("there was no generic parameter associated with the arg");
                             }
+                            Def::Err => tcx.types.err,
                             x => bug!("unexpected const parent path def {:?}", x),
                         }
                     }

src/test/ui/const_generics/const-arg-in-unknown-fn.rs

@@ -0,0 +1,15 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![feature(const_generics)]
+
+fn main() {
+    find_me_not::<18>(); //~ ERROR cannot find function
+}

src/test/ui/const_generics/const-arg-in-unknown-fn.stderr

@@ -0,0 +1,9 @@
+error[E0425]: cannot find function `find_me_not` in this scope
+  --> $DIR/const-arg-in-unknown-fn.rs:14:5
+   |
+LL |     find_me_not::<18>(); //~ ERROR cannot find function
+   |     ^^^^^^^^^^^ not found in this scope
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0425`.