LazyCell/LazyLock stabilized in nightly

A good time to refresh my Rust folder as a whole to see what features got stabilized, removed, or subsumed.

My current list of used unstable features is down to 20.
Some lang, some lib.
A couple incomplete.
Some are more important than others.

#![feature(adt_const_params)]
#![feature(async_closure)]
#![feature(const_type_name)]
#![feature(duration_constants)]
#![feature(extract_if)]
#![feature(generic_arg_infer)]
#![feature(impl_trait_in_assoc_type)]
#![feature(iter_array_chunks)]
#![feature(let_chains)]
#![feature(macro_metavar_expr)]
#![feature(map_try_insert)]
#![feature(never_type)]
#![feature(once_cell_try)]
#![feature(proc_macro_hygiene)]
#![feature(specialization)]
#![feature(step_trait)]
#![feature(stmt_expr_attributes)]
#![feature(try_blocks)]
#![feature(try_find)]
#![feature(type_changing_struct_update)]

DISCLAIMER: this is not an endorsement of try_blocks 😐