std::thread_local, std::thread::local, std::thread::local_impl, std::sys_common::thread_local_key, std::sys_common::thread_local_dtor, std::sys::thread_local_key, etc. etc. are all messy and form quite a confusing maze. Just look at this map I tried to draw of it all:

AAAaaaaAaa

Time to clean it up.

And maybe also fix some bugs while we're at it. ^^

• Initial name and module cleanup without touching implementation: Restructure and rename std thread_local internals to make it less of a maze #110861
• Remove unused Key type: Remove unused std::sys_common::thread_local_key::Key #110898
• Fix panic-in-drop handling
  • A thread_local! with a const initializer and a panicking drop impl unwinds through an extern "C" frame #112285
    • Avoid unwind across extern "C" in thread_local::fast_local #112292
• Stop calling everything Key, because most of those things are actually not keys, and drop LazyKeyInner
  • Rewrite native thread-local storage #116123
  • Simplify key-based thread locals #122494
  • Rewrite TLS on platforms without threads #123724
• Reduce the amount of code in the thread_local!{} expansion. Make TLS accessors closures that return pointers #125525
• Use *const T rather than &'static T when it's not really 'static: Make TLS accessors closures that return pointers #125525
• Clean up implementation more
  • std: refactor the TLS implementation #126523
  • std: separate TLS key creation from TLS access #126953
  • std: use duplicate thread local state in tests #128135
• Store thread ID and stack guard range in thread locals without destructors (on platforms with #[thread_local])?
  • Stack guard range: Refactor stack overflow handling #123265
  • thread ID: Use ThreadId instead of TLS-address in ReentrantLock #124881
• Make thread::current thread local more efficient and make it available in (most) TLS destructors: std: make thread::current available in all thread_local! destructors #127912
• Detect stack overflow in TLS destructors: std: detect stack overflows in TLS destructors on UNIX #131282

Related issues to solve, maybe:

• Consider documenting that (parts of?) stdlib must not be used before/after main #110708
• Stack overflow not caught in Drop for TLS data #111272
  • Stack overflow in thread local's drop rendered as a segmentation fault. #109785
• Maybe this shouldn't work? See conversation around this comment.
• ...?