Just pass in NodeId to FunctionContext::new instead of looking it up.

src/test/run-pass/auxiliary/xcrate_generic_fn_nested_return.rs

@@ -0,0 +1,26 @@
+// Copyright 2016 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.
+
+pub struct Request {
+    pub id: String,
+    pub arg: String,
+}
+
+pub fn decode<T>() -> Result<Request, ()> {
+    (|| {
+        Ok(Request {
+            id: "hi".to_owned(),
+            arg: match Err(()) {
+                Ok(v) => v,
+                Err(e) => return Err(e)
+            },
+        })
+    })()
+}

src/test/run-pass/xcrate_generic_fn_nested_return.rs

@@ -0,0 +1,17 @@
+// Copyright 2016 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.
+
+// aux-build:xcrate_generic_fn_nested_return.rs
+
+extern crate xcrate_generic_fn_nested_return as test;
+
+pub fn main() {
+    assert!(test::decode::<()>().is_err());
+}