Rollup merge of #69959 - alexcrichton:fix-panic-in-print, r=Mark-Simulacrum

std: Don't abort process when printing panics in tests

This commit fixes an issue when using `set_print` and friends, notably
used by libtest, to avoid aborting the process if printing panics. This
previously panicked due to borrowing a mutable `RefCell` twice, and this
is worked around by borrowing these cells for less time, instead
taking out and removing contents temporarily.

Closes #69558

src/test/ui/panic-while-printing.rs

@@ -0,0 +1,24 @@
+// run-pass
+// ignore-emscripten no subprocess support
+
+#![feature(set_stdio)]
+
+use std::fmt;
+use std::fmt::{Display, Formatter};
+use std::io::set_panic;
+
+pub struct A;
+
+impl Display for A {
+    fn fmt(&self, _f: &mut Formatter<'_>) -> fmt::Result {
+        panic!();
+    }
+}
+
+fn main() {
+    set_panic(Some(Box::new(Vec::new())));
+    assert!(std::panic::catch_unwind(|| {
+        eprintln!("{}", A);
+    })
+    .is_err());
+}

src/test/ui/test-panic-while-printing.rs

@@ -0,0 +1,24 @@
+// compile-flags:--test
+// run-pass
+// ignore-emscripten no subprocess support
+
+use std::fmt;
+use std::fmt::{Display, Formatter};
+
+pub struct A(Vec<u32>);
+
+impl Display for A {
+    fn fmt(&self, _f: &mut Formatter<'_>) -> fmt::Result {
+        self.0[0];
+        Ok(())
+    }
+}
+
+#[test]
+fn main() {
+    let result = std::panic::catch_unwind(|| {
+        let a = A(vec![]);
+        eprintln!("{}", a);
+    });
+    assert!(result.is_err());
+}