warning: a method with this name may be added to the standard library in the future
  --> $DIR/inference_unstable.rs:16:20
   |
LL |     assert_eq!('x'.ipu_flatten(), 1);
   |                    ^^^^^^^^^^^
   |
   = note: `#[warn(unstable_name_collisions)]` on by default
   = warning: once this method is added to the standard library, the ambiguity may cause an error or change in behavior!
   = note: for more information, see issue #48919 <https://github.com/rust-lang/rust/issues/48919>
   = help: call with fully qualified syntax `inference_unstable_itertools::IpuItertools::ipu_flatten(...)` to keep using the current method
   = help: add `#![feature(ipu_flatten)]` to the crate attributes to enable `inference_unstable_iterator::IpuIterator::ipu_flatten`