Auto merge of #26966 - nagisa:tail-init, r=alexcrichton

Fixes #26906

diff --combined src/libcollectionstest/lib.rs
index 87c7449540c7953a8ec8afc0364c486d77d7c5a3,de6dcc9adcb87c4c952e5702e5d91433b4a3d348..6bf7380fdeb500138cc923157607184a17f7c39d
--- 1/src/libcollectionstest/lib.rs
--- 2/src/libcollectionstest/lib.rs
+++ b/src/libcollectionstest/lib.rs
@@@ -36,7 -36,7 +36,7 @@@
  #![feature(rustc_private)]
  #![feature(slice_bytes)]
  #![feature(slice_chars)]
- #![feature(slice_extras)]
+ #![feature(slice_splits)]
  #![feature(slice_position_elem)]
  #![feature(split_off)]
  #![feature(step_by)]
@@@ -44,7 -44,6 +44,7 @@@
  #![feature(str_escape)]
  #![feature(str_match_indices)]
  #![feature(str_utf16)]
 +#![feature(box_str)]
  #![feature(subslice_offset)]
  #![feature(test)]
  #![feature(unboxed_closures)]
@@@ -52,9 -51,10 +52,10 @@@
  #![feature(vec_deque_retain)]
  #![feature(vec_from_raw_buf)]
  #![feature(vec_push_all)]
- #![feature(vec_split_off)]
  #![feature(vecmap)]
  
+ #![allow(deprecated)]
+ 
  #[macro_use] extern crate log;
  
  extern crate collections;