Alternate fix for issue #24085

src/librustc/middle/traits/mod.rs

@@ -322,7 +322,17 @@ pub fn evaluate_builtin_bound<'a,'tcx>(infcx: &InferCtxt<'a,'tcx>,
     // anyhow).
     let cause = ObligationCause::misc(span, ast::DUMMY_NODE_ID);
 
-    fulfill_cx.register_builtin_bound(infcx, ty, bound, cause);
+    // Relax region constraints that result from trait selection by
+    // inserting an inference variable.  This mimics the behavior
+    // of method confirmation where fresh inference variables are
+    // substituted into the method self type, which is then unified
+    // with the adjusted receiver type and handed to trait selection.
+    let relax_ty = infcx.next_ty_var();
+    try!(infcx.sub_types(false, infer::Misc(span), ty, relax_ty).map_err(|_| Unimplemented));
+    let relax_ty = infcx.resolve_type_vars_if_possible(&relax_ty);
+    debug!("relax_ty: {}", relax_ty.repr(infcx.tcx));
+
+    fulfill_cx.register_builtin_bound(infcx, relax_ty, bound, cause);
 
     // Note: we only assume something is `Copy` if we can
     // *definitively* show that it implements `Copy`. Otherwise,

src/test/run-pass/traits-issue-24085.rs

@@ -0,0 +1,29 @@
+// Copyright 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.
+
+// Test that trait selection for Copy does not introduce
+// bad region constraints.  Issue #24085.
+
+#[derive(Clone, Copy)]
+enum Path<'a:'b, 'b> {
+    Data(&'a i32),
+    Link(&'a i32, &'b Path<'a, 'b>)
+}
+
+fn foo<'a,'b,F>(_p: Path<'a, 'b>, _f: F)
+                where F: for<'c> FnMut(&Path<'a, 'c>) {
+}
+
+fn main() {
+    let y = 0;
+    let p = Path::Data(&y);
+
+    foo(p, |x| {*x;});
+}