Rollup merge of #122882 - Zoxc:panic-output-panic, r=Amanieu

Avoid a panic in `set_output_capture` in the default panic handler

This avoid a panic in the default panic handler by not using `set_output_capture` as `OUTPUT_CAPTURE.with` may panic once `OUTPUT_CAPTURE` is dropped.

A new non-panicking `try_set_output_capture` variant of `set_output_capture` is added for use in the default panic handler.

library/std/src/io/mod.rs

@@ -311,14 +311,14 @@ pub use self::buffered::WriterPanicked;
 #[unstable(feature = "raw_os_error_ty", issue = "107792")]
 pub use self::error::RawOsError;
 pub(crate) use self::stdio::attempt_print_to_stderr;
-#[unstable(feature = "internal_output_capture", issue = "none")]
-#[doc(no_inline, hidden)]
-pub use self::stdio::set_output_capture;
 #[stable(feature = "is_terminal", since = "1.70.0")]
 pub use self::stdio::IsTerminal;
 #[unstable(feature = "print_internals", issue = "none")]
 #[doc(hidden)]
 pub use self::stdio::{_eprint, _print};
+#[unstable(feature = "internal_output_capture", issue = "none")]
+#[doc(no_inline, hidden)]
+pub use self::stdio::{set_output_capture, try_set_output_capture};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::{
     buffered::{BufReader, BufWriter, IntoInnerError, LineWriter},

library/std/src/io/stdio.rs

@@ -15,6 +15,7 @@ use crate::panic::{RefUnwindSafe, UnwindSafe};
 use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sync::{Arc, Mutex, MutexGuard, OnceLock, ReentrantLock, ReentrantLockGuard};
 use crate::sys::stdio;
+use crate::thread::AccessError;
 
 type LocalStream = Arc<Mutex<Vec<u8>>>;
 
@@ -1064,12 +1065,31 @@ impl fmt::Debug for StderrLock<'_> {
 )]
 #[doc(hidden)]
 pub fn set_output_capture(sink: Option<LocalStream>) -> Option<LocalStream> {
+    try_set_output_capture(sink).expect(
+        "cannot access a Thread Local Storage value \
+         during or after destruction",
+    )
+}
+
+/// Tries to set the thread-local output capture buffer and returns the old one.
+/// This may fail once thread-local destructors are called. It's used in panic
+/// handling instead of `set_output_capture`.
+#[unstable(
+    feature = "internal_output_capture",
+    reason = "this function is meant for use in the test crate \
+    and may disappear in the future",
+    issue = "none"
+)]
+#[doc(hidden)]
+pub fn try_set_output_capture(
+    sink: Option<LocalStream>,
+) -> Result<Option<LocalStream>, AccessError> {
     if sink.is_none() && !OUTPUT_CAPTURE_USED.load(Ordering::Relaxed) {
         // OUTPUT_CAPTURE is definitely None since OUTPUT_CAPTURE_USED is false.
-        return None;
+        return Ok(None);
     }
     OUTPUT_CAPTURE_USED.store(true, Ordering::Relaxed);
-    OUTPUT_CAPTURE.with(move |slot| slot.replace(sink))
+    OUTPUT_CAPTURE.try_with(move |slot| slot.replace(sink))
 }
 
 /// Write `args` to the capture buffer if enabled and possible, or `global_s`

library/std/src/panicking.rs

@@ -24,11 +24,11 @@ use crate::sys_common::backtrace;
 use crate::thread;
 
 #[cfg(not(test))]
-use crate::io::set_output_capture;
+use crate::io::try_set_output_capture;
 // make sure to use the stderr output configured
 // by libtest in the real copy of std
 #[cfg(test)]
-use realstd::io::set_output_capture;
+use realstd::io::try_set_output_capture;
 
 // Binary interface to the panic runtime that the standard library depends on.
 //
@@ -284,9 +284,9 @@ fn default_hook(info: &PanicInfo<'_>) {
         }
     };
 
-    if let Some(local) = set_output_capture(None) {
+    if let Ok(Some(local)) = try_set_output_capture(None) {
         write(&mut *local.lock().unwrap_or_else(|e| e.into_inner()));
-        set_output_capture(Some(local));
+        try_set_output_capture(Some(local)).ok();
     } else if let Some(mut out) = panic_output() {
         write(&mut out);
     }