Auto merge of #110861 - m-ou-se:thread-local-restructure, r=workingjubilee

Restructure and rename std thread_local internals to make it less of a maze

Every time I try to work on std's thread local internals, it feels like I'm trying to navigate a confusing maze made of macros, deeply nested modules, and types with multiple names/aliases. Time to clean it up a bit.

This PR:

- Exports `Key` with its own name (`Key`), instead of `__LocalKeyInner`
- Uses `pub macro` to put `__thread_local_inner` into a (unstable, hidden) module, removing `#[macro_export]`, removing it from the crate root.
- Removes the `__` from `__thread_local_inner`.
- Removes a few unnecessary `allow_internal_unstable` features from the macros
- Removes the `libstd_thread_internals` feature. (Merged with `thread_local_internals`.)
    - And removes it from the unstable book
- Gets rid of the deeply nested modules for the `Key` definitions (`mod fast` / `mod os` / `mod statik`).
- Turns a `#[cfg]` mess into a single `cfg_if`, now that there's no `#[macro_export]` anymore that breaks with `cfg_if`.
- Simplifies the `cfg_if` conditions to not repeat the conditions.
- Removes useless `normalize-stderr-test`, which were left over from when the `Key` types had different names on different platforms.
- Removes a seemingly unnecessary `realstd` re-export on `cfg(test)`.

This PR changes nothing about the thread local implementation. That's for a later PR. (Which should hopefully be easier once all this stuff is a bit cleaned up.)

tests/ui/macros/macro-local-data-key-priv.stderr

@@ -9,7 +9,7 @@ note: the constant `baz` is defined here
    |
 LL |     thread_local!(static baz: f64 = 0.0);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: this error originates in the macro `$crate::__thread_local_inner` which comes from the expansion of the macro `thread_local` (in Nightly builds, run with -Z macro-backtrace for more info)
+   = note: this error originates in the macro `$crate::thread::local_impl::thread_local_inner` which comes from the expansion of the macro `thread_local` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error
 

tests/ui/threads-sendsync/issue-43733-2.rs

@@ -21,7 +21,7 @@ impl<T> Key<T> {
 }
 
 #[cfg(target_thread_local)]
-use std::thread::__LocalKeyInner as Key;
+use std::thread::local_impl::Key;
 
 static __KEY: Key<()> = Key::new();
 //~^ ERROR `UnsafeCell<Option<()>>` cannot be shared between threads

tests/ui/threads-sendsync/issue-43733.mir.stderr

@@ -1,5 +1,5 @@
 error[E0133]: call to unsafe function is unsafe and requires unsafe function or block
-  --> $DIR/issue-43733.rs:21:5
+  --> $DIR/issue-43733.rs:19:5
    |
 LL |     __KEY.get(Default::default)
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function
@@ -7,7 +7,7 @@ LL |     __KEY.get(Default::default)
    = note: consult the function's documentation for information on how to avoid undefined behavior
 
 error[E0133]: call to unsafe function is unsafe and requires unsafe function or block
-  --> $DIR/issue-43733.rs:26:42
+  --> $DIR/issue-43733.rs:24:42
    |
 LL | static FOO: std::thread::LocalKey<Foo> = std::thread::LocalKey::new(__getit);
    |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function

tests/ui/threads-sendsync/issue-43733.rs

@@ -1,8 +1,6 @@
 // ignore-wasm32
 // revisions: mir thir
 // [thir]compile-flags: -Z thir-unsafeck
-// normalize-stderr-test: "__LocalKeyInner::<T>::get" -> "$$LOCALKEYINNER::<T>::get"
-// normalize-stderr-test: "__LocalKeyInner::<T>::get" -> "$$LOCALKEYINNER::<T>::get"
 #![feature(thread_local)]
 #![feature(cfg_target_thread_local, thread_local_internals)]
 
@@ -12,15 +10,15 @@ type Foo = std::cell::RefCell<String>;
 
 #[cfg(target_thread_local)]
 #[thread_local]
-static __KEY: std::thread::__LocalKeyInner<Foo> = std::thread::__LocalKeyInner::new();
+static __KEY: std::thread::local_impl::Key<Foo> = std::thread::local_impl::Key::new();
 
 #[cfg(not(target_thread_local))]
-static __KEY: std::thread::__LocalKeyInner<Foo> = std::thread::__LocalKeyInner::new();
+static __KEY: std::thread::local_impl::Key<Foo> = std::thread::local_impl::Key::new();
 
 fn __getit(_: Option<&mut Option<RefCell<String>>>) -> std::option::Option<&'static Foo> {
     __KEY.get(Default::default)
     //[mir]~^ ERROR call to unsafe function is unsafe
-    //[thir]~^^ ERROR call to unsafe function `__
+    //[thir]~^^ ERROR call to unsafe function `Key::<T>::get`
 }
 
 static FOO: std::thread::LocalKey<Foo> = std::thread::LocalKey::new(__getit);

tests/ui/threads-sendsync/issue-43733.thir.stderr

@@ -1,5 +1,5 @@
-error[E0133]: call to unsafe function `$LOCALKEYINNER::<T>::get` is unsafe and requires unsafe function or block
-  --> $DIR/issue-43733.rs:21:5
+error[E0133]: call to unsafe function `Key::<T>::get` is unsafe and requires unsafe function or block
+  --> $DIR/issue-43733.rs:19:5
    |
 LL |     __KEY.get(Default::default)
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function
@@ -7,7 +7,7 @@ LL |     __KEY.get(Default::default)
    = note: consult the function's documentation for information on how to avoid undefined behavior
 
 error[E0133]: call to unsafe function `LocalKey::<T>::new` is unsafe and requires unsafe function or block
-  --> $DIR/issue-43733.rs:26:42
+  --> $DIR/issue-43733.rs:24:42
    |
 LL | static FOO: std::thread::LocalKey<Foo> = std::thread::LocalKey::new(__getit);
    |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function