don't unwrap non-local span

src/librustc_typeck/check/compare_method.rs

@@ -110,30 +110,40 @@ pub fn compare_impl_method<'a, 'tcx>(ccx: &CrateCtxt<'a, 'tcx>,
             _ => bug!("{:?} is not a method", impl_m)
         };
 
-        struct_span_err!(tcx.sess, span, E0049,
+        let mut err = struct_span_err!(tcx.sess, span, E0049,
             "method `{}` has {} type parameter{} \
              but its trait declaration has {} type parameter{}",
             trait_m.name,
             num_impl_m_type_params,
             if num_impl_m_type_params == 1 {""} else {"s"},
             num_trait_m_type_params,
-            if num_trait_m_type_params == 1 {""} else {"s"})
-            .span_label(trait_item_span.unwrap(),
-                        &format!("expected {}",
-                                 &if num_trait_m_type_params != 1 {
-                                     format!("{} type parameters",
-                                             num_trait_m_type_params)
-                                 } else {
-                                     format!("{} type parameter",
-                                             num_trait_m_type_params)
-                                 }))
-            .span_label(span, &format!("found {}",
-                                       &if num_impl_m_type_params != 1 {
-                                           format!("{} type parameters", num_impl_m_type_params)
-                                       } else {
-                                           format!("1 type parameter")
-                                       }))
-            .emit();
+            if num_trait_m_type_params == 1 {""} else {"s"});
+
+        let mut suffix = None;
+
+        if let Some(span) = trait_item_span {
+            err.span_label(span,
+                           &format!("expected {}",
+                                    &if num_trait_m_type_params != 1 {
+                                        format!("{} type parameters", num_trait_m_type_params)
+                                    } else {
+                                        format!("{} type parameter", num_trait_m_type_params)
+                                    }));
+        } else {
+            suffix = Some(format!(", expected {}", num_trait_m_type_params));
+        }
+
+        err.span_label(span,
+                       &format!("found {}{}",
+                                &if num_impl_m_type_params != 1 {
+                                    format!("{} type parameters", num_impl_m_type_params)
+                                } else {
+                                    format!("1 type parameter")
+                                },
+                                suffix.as_ref().map(|s| &s[..]).unwrap_or("")));
+
+        err.emit();
+
         return;
     }
 

src/test/compile-fail/auxiliary/issue-36708.rs

@@ -0,0 +1,15 @@
+// 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.
+
+#![crate_type = "lib"]
+
+pub trait Foo {
+    fn foo();
+}

src/test/compile-fail/issue-36708.rs

@@ -0,0 +1,23 @@
+// 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:issue-36708.rs
+
+extern crate issue_36708 as lib;
+
+struct Bar;
+
+impl lib::Foo for Bar {
+    fn foo<T>() {}
+    //~^ ERROR E0049
+    //~| NOTE found 1 type parameter, expected 0
+}
+
+fn main() {}