Merge from rustc

Author: The Miri Conjob Bot

Cargo.lock

@@ -2541,9 +2541,6 @@ dependencies = [
 [[package]]
 name = "miropt-test-tools"
 version = "0.1.0"
-dependencies = [
- "regex",
-]
 
 [[package]]
 name = "native-tls"

compiler/rustc_ast/src/lib.rs

@@ -12,10 +12,12 @@
 #![allow(internal_features)]
 #![feature(rustdoc_internals)]
 #![feature(associated_type_bounds)]
+#![feature(associated_type_defaults)]
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
 #![cfg_attr(bootstrap, feature(min_specialization))]
+#![feature(never_type)]
 #![feature(negative_impls)]
 #![feature(stmt_expr_attributes)]