Rollup merge of #144022 - connortsui20:sync_nonpoison, r=tgross35

Implementation: `#[feature(sync_nonpoison)]`, `#[feature(nonpoison_mutex)]`

Continuation of #134663

Tracking Issue: #134645

This PR implements a new `sync/nonpoison` module, as well as the `nonpoison` variant of the `Mutex` lock.

There are 2 main changes here, the first is the new `nonpoison::mutex` module, and the second is the `mutex` integration tests.

For the `nonpoison::mutex` module, I did my best to align it with the current state of the `poison::mutex` module. This means that several unstable features (`mapped_lock_guards`, `lock_value_accessors`, and `mutex_data_ptr`) are also in the new `nonpoison::mutex` module, under their respective feature gates. Everything else in that file is under the correct feature gate (`#[unstable(feature = "nonpoison_mutex", issue = "134645")]`).

Everything in the `nonpoison::mutex` file is essentially identical in spirit, as we are simply removing the error case from the original `poison::mutex`.

The second big change is in the integration tests. I created a macro called that allows us to duplicate tests that are "generic" over the different mutex types, in that the poison mutex is always `unwrap`ped.

~~I think that there is an argument against doing this, as it can make the tests a bit harder to understand (and language server capabilities are weaker within macros), but I think the benefit of code deduplication here is worth it. Note that it is definitely possible to generalize this (with a few tweaks) to testing the other `nonpoison` locks when they eventually get implemented, but I'll leave that for a later discussion.~~

Author: Zalathar

library/std/src/sync/mod.rs

@@ -225,6 +225,8 @@ pub use self::poison::{MappedMutexGuard, MappedRwLockReadGuard, MappedRwLockWrit
 pub mod mpmc;
 pub mod mpsc;
 
+#[unstable(feature = "sync_nonpoison", issue = "134645")]
+pub mod nonpoison;
 #[unstable(feature = "sync_poison_mod", issue = "134646")]
 pub mod poison;
 

library/std/src/sync/nonpoison.rs

@@ -0,0 +1,37 @@
+//! Non-poisoning synchronous locks.
+//!
+//! The difference from the locks in the [`poison`] module is that the locks in this module will not
+//! become poisoned when a thread panics while holding a guard.
+//!
+//! [`poison`]: super::poison
+
+use crate::fmt;
+
+/// A type alias for the result of a nonblocking locking method.
+#[unstable(feature = "sync_nonpoison", issue = "134645")]
+pub type TryLockResult<Guard> = Result<Guard, WouldBlock>;
+
+/// A lock could not be acquired at this time because the operation would otherwise block.
+#[unstable(feature = "sync_nonpoison", issue = "134645")]
+pub struct WouldBlock;
+
+#[unstable(feature = "sync_nonpoison", issue = "134645")]
+impl fmt::Debug for WouldBlock {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        "WouldBlock".fmt(f)
+    }
+}
+
+#[unstable(feature = "sync_nonpoison", issue = "134645")]
+impl fmt::Display for WouldBlock {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        "try_lock failed because the operation would block".fmt(f)
+    }
+}
+
+#[unstable(feature = "mapped_lock_guards", issue = "117108")]
+pub use self::mutex::MappedMutexGuard;
+#[unstable(feature = "nonpoison_mutex", issue = "134645")]
+pub use self::mutex::{Mutex, MutexGuard};
+
+mod mutex;