{rustc::util -> rustc_data_structures}::captures

src/librustc_data_structures/captures.rs

@@ -0,0 +1,10 @@
+/// "Signaling" trait used in impl trait to tag lifetimes that you may
+/// need to capture but don't really need for other reasons.
+/// Basically a workaround; see [this comment] for details.
+///
+/// [this comment]: https://github.com/rust-lang/rust/issues/34511#issuecomment-373423999
+// FIXME(eddyb) false positive, the lifetime parameter is "phantom" but needed.
+#[allow(unused_lifetimes)]
+pub trait Captures<'a> {}
+
+impl<'a, T: ?Sized> Captures<'a> for T {}

src/librustc_data_structures/lib.rs

@@ -67,6 +67,7 @@ macro_rules! unlikely {
 pub mod base_n;
 pub mod binary_search_util;
 pub mod box_region;
+pub mod captures;
 pub mod const_cstr;
 pub mod flock;
 pub mod fx;