support impl trait for needless lifetimes

clippy_lints/src/lifetimes.rs

@@ -281,6 +281,13 @@ impl<'a, 'tcx> Visitor<'tcx> for RefVisitor<'a, 'tcx> {
             TyPath(ref path) => {
                 self.collect_anonymous_lifetimes(path, ty);
             },
+            TyImplTrait(ref param_bounds) => {
+                for bound in param_bounds {
+                    if let RegionTyParamBound(_) = *bound {
+                        self.record(&None);
+                    }
+                }
+            }
             _ => (),
         }
         walk_ty(self, ty);

tests/run-pass/needless_lifetimes_impl_trait.rs

@@ -0,0 +1,22 @@
+#![feature(plugin)]
+#![plugin(clippy)]
+#![feature(conservative_impl_trait)]
+#![deny(needless_lifetime)]
+
+trait Foo {}
+
+struct Bar {}
+
+struct Baz<'a> {
+    bar: &'a Bar,
+}
+
+impl<'a> Foo for Baz<'a> {}
+
+impl Bar {
+    fn baz<'a>(&'a self) -> impl Foo + 'a {
+        Baz { bar: self }
+    }
+}
+
+fn main() {}