Fix ICE with unresolved associated items in closures (fixes #28971)

Author: Manishearth

src/librustc/middle/mem_categorization.rs

@@ -1196,7 +1196,18 @@ impl<'t, 'a,'tcx> MemCategorizationContext<'t, 'a, 'tcx> {
 
         (*op)(self, cmt.clone(), pat);
 
-        let opt_def = self.tcx().def_map.borrow().get(&pat.id).map(|d| d.full_def());
+        let opt_def = if let Some(path_res) = self.tcx().def_map.borrow().get(&pat.id) {
+            if path_res.depth != 0 {
+                // Since patterns can be associated constants
+                // which are resolved during typeck, we might have
+                // some unresolved patterns reaching this stage
+                // without aborting
+                return Err(());
+            }
+            Some(path_res.full_def())
+        } else {
+            None
+        };
 
         // Note: This goes up here (rather than within the PatEnum arm
         // alone) because struct patterns can refer to struct types or

src/test/compile-fail/issue-28971.rs

@@ -0,0 +1,27 @@
+// Copyright 2012-2015 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.
+
+// This should not cause an ICE
+
+enum Foo {
+    Bar(u8)
+}
+fn main(){
+    foo(|| {
+        match Foo::Bar(1) {
+            Foo::Baz(..) => (), //~ ERROR no associated
+            _ => (),
+        }
+    });
+}
+
+fn foo<F>(f: F) where F: FnMut() {
+    f();
+}