Merge set_panic and set_print into set_output_capture.

There were no use cases for setting them separately.
Merging them simplifies some things.

library/std/src/io/stdio.rs

@@ -14,37 +14,29 @@ use crate::sync::{Arc, Mutex, MutexGuard};
 use crate::sys::stdio;
 use crate::sys_common;
 use crate::sys_common::remutex::{ReentrantMutex, ReentrantMutexGuard};
-use crate::thread::LocalKey;
 
 type LocalStream = Arc<Mutex<Vec<u8>>>;
 
 thread_local! {
-    /// Used by the test crate to capture the output of the print! and println! macros.
-    static LOCAL_STDOUT: Cell<Option<LocalStream>> = {
+    /// Used by the test crate to capture the output of the print macros and panics.
+    static OUTPUT_CAPTURE: Cell<Option<LocalStream>> = {
         Cell::new(None)
     }
 }
 
-thread_local! {
-    /// Used by the test crate to capture the output of the eprint! and eprintln! macros, and panics.
-    static LOCAL_STDERR: Cell<Option<LocalStream>> = {
-        Cell::new(None)
-    }
-}
-
-/// Flag to indicate LOCAL_STDOUT and/or LOCAL_STDERR is used.
+/// Flag to indicate OUTPUT_CAPTURE is used.
 ///
-/// If both are None and were never set on any thread, this flag is set to
-/// false, and both LOCAL_STDOUT and LOCAL_STDOUT can be safely ignored on all
-/// threads, saving some time and memory registering an unused thread local.
+/// If it is None and was never set on any thread, this flag is set to false,
+/// and OUTPUT_CAPTURE can be safely ignored on all threads, saving some time
+/// and memory registering an unused thread local.
 ///
-/// Note about memory ordering: This contains information about whether two
-/// thread local variables might be in use. Although this is a global flag, the
+/// Note about memory ordering: This contains information about whether a
+/// thread local variable might be in use. Although this is a global flag, the
 /// memory ordering between threads does not matter: we only want this flag to
-/// have a consistent order between set_print/set_panic and print_to *within
+/// have a consistent order between set_output_capture and print_to *within
 /// the same thread*. Within the same thread, things always have a perfectly
 /// consistent order. So Ordering::Relaxed is fine.
-static LOCAL_STREAMS: AtomicBool = AtomicBool::new(false);
+static OUTPUT_CAPTURE_USED: AtomicBool = AtomicBool::new(false);
 
 /// A handle to a raw instance of the standard input stream of this process.
 ///
@@ -890,70 +882,24 @@ impl fmt::Debug for StderrLock<'_> {
     }
 }
 
-/// Resets the thread-local stderr handle to the specified writer
-///
-/// This will replace the current thread's stderr handle, returning the old
-/// handle. All future calls to `panic!` and friends will emit their output to
-/// this specified handle.
-///
-/// Note that this does not need to be called for all new threads; the default
-/// output handle is to the process's stderr stream.
+/// Sets the thread-local output capture buffer and returns the old one.
 #[unstable(
-    feature = "set_stdio",
-    reason = "this function may disappear completely or be replaced \
-                     with a more general mechanism",
+    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 set_panic(sink: Option<LocalStream>) -> Option<LocalStream> {
-    if sink.is_none() && !LOCAL_STREAMS.load(Ordering::Relaxed) {
-        // LOCAL_STDERR is definitely None since LOCAL_STREAMS is false.
+pub fn set_output_capture(sink: Option<LocalStream>) -> Option<LocalStream> {
+    if sink.is_none() && !OUTPUT_CAPTURE_USED.load(Ordering::Relaxed) {
+        // OUTPUT_CAPTURE is definitely None since OUTPUT_CAPTURE_USED is false.
         return None;
     }
-    LOCAL_STREAMS.store(true, Ordering::Relaxed);
-    LOCAL_STDERR.with(move |slot| slot.replace(sink))
+    OUTPUT_CAPTURE_USED.store(true, Ordering::Relaxed);
+    OUTPUT_CAPTURE.with(move |slot| slot.replace(sink))
 }
 
-/// Resets the thread-local stdout handle to the specified writer
-///
-/// This will replace the current thread's stdout handle, returning the old
-/// handle. All future calls to `print!` and friends will emit their output to
-/// this specified handle.
-///
-/// Note that this does not need to be called for all new threads; the default
-/// output handle is to the process's stdout stream.
-#[unstable(
-    feature = "set_stdio",
-    reason = "this function may disappear completely or be replaced \
-                     with a more general mechanism",
-    issue = "none"
-)]
-#[doc(hidden)]
-pub fn set_print(sink: Option<LocalStream>) -> Option<LocalStream> {
-    if sink.is_none() && !LOCAL_STREAMS.load(Ordering::Relaxed) {
-        // LOCAL_STDOUT is definitely None since LOCAL_STREAMS is false.
-        return None;
-    }
-    LOCAL_STREAMS.store(true, Ordering::Relaxed);
-    LOCAL_STDOUT.with(move |slot| slot.replace(sink))
-}
-
-pub(crate) fn clone_io() -> (Option<LocalStream>, Option<LocalStream>) {
-    // Don't waste time when LOCAL_{STDOUT,STDERR} are definitely None.
-    if !LOCAL_STREAMS.load(Ordering::Relaxed) {
-        return (None, None);
-    }
-
-    let clone = |cell: &Cell<Option<LocalStream>>| {
-        let s = cell.take();
-        cell.set(s.clone());
-        s
-    };
-
-    (LOCAL_STDOUT.with(clone), LOCAL_STDERR.with(clone))
-}
-
-/// Write `args` to output stream `local_s` if possible, `global_s`
+/// Write `args` to the capture buffer if enabled and possible, or `global_s`
 /// otherwise. `label` identifies the stream in a panic message.
 ///
 /// This function is used to print error messages, so it takes extra
@@ -963,16 +909,12 @@ pub(crate) fn clone_io() -> (Option<LocalStream>, Option<LocalStream>) {
 /// thread, it will just fall back to the global stream.
 ///
 /// However, if the actual I/O causes an error, this function does panic.
-fn print_to<T>(
-    args: fmt::Arguments<'_>,
-    local_s: &'static LocalKey<Cell<Option<LocalStream>>>,
-    global_s: fn() -> T,
-    label: &str,
-) where
+fn print_to<T>(args: fmt::Arguments<'_>, global_s: fn() -> T, label: &str)
+where
     T: Write,
 {
-    if LOCAL_STREAMS.load(Ordering::Relaxed)
-        && local_s.try_with(|s| {
+    if OUTPUT_CAPTURE_USED.load(Ordering::Relaxed)
+        && OUTPUT_CAPTURE.try_with(|s| {
             // Note that we completely remove a local sink to write to in case
             // our printing recursively panics/prints, so the recursive
             // panic/print goes to the global sink instead of our local sink.
@@ -982,7 +924,7 @@ fn print_to<T>(
             })
         }) == Ok(Some(()))
     {
-        // Succesfully wrote to local stream.
+        // Succesfully wrote to capture buffer.
         return;
     }
 
@@ -999,7 +941,7 @@ fn print_to<T>(
 #[doc(hidden)]
 #[cfg(not(test))]
 pub fn _print(args: fmt::Arguments<'_>) {
-    print_to(args, &LOCAL_STDOUT, stdout, "stdout");
+    print_to(args, stdout, "stdout");
 }
 
 #[unstable(
@@ -1010,7 +952,7 @@ pub fn _print(args: fmt::Arguments<'_>) {
 #[doc(hidden)]
 #[cfg(not(test))]
 pub fn _eprint(args: fmt::Arguments<'_>) {
-    print_to(args, &LOCAL_STDERR, stderr, "stderr");
+    print_to(args, stderr, "stderr");
 }
 
 #[cfg(test)]