Rollup merge of #73302 - JakobDegen:should-panic-documentation, r=Mark-Simulacrum

Adjusted some doctests in libcore to use `should_panic`.

Fixes #73196 .

I grepped libstd and libcore for all the instances of this pattern that I could find, but its possible that I missed some of course. If anyone knows of any more, please let me know and I will add them to the PR.

src/libcore/cell.rs

@@ -778,18 +778,13 @@ impl<T: ?Sized> RefCell<T> {
     ///
     /// An example of panic:
     ///
-    /// ```
+    /// ```should_panic
     /// use std::cell::RefCell;
-    /// use std::thread;
-    ///
-    /// let result = thread::spawn(move || {
-    ///    let c = RefCell::new(5);
-    ///    let m = c.borrow_mut();
     ///
-    ///    let b = c.borrow(); // this causes a panic
-    /// }).join();
+    /// let c = RefCell::new(5);
     ///
-    /// assert!(result.is_err());
+    /// let m = c.borrow_mut();
+    /// let b = c.borrow(); // this causes a panic
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
@@ -858,18 +853,13 @@ pub fn try_borrow(&self) -> Result<Ref<'_, T>, BorrowError> {
     ///
     /// An example of panic:
     ///
-    /// ```
+    /// ```should_panic
     /// use std::cell::RefCell;
-    /// use std::thread;
-    ///
-    /// let result = thread::spawn(move || {
-    ///    let c = RefCell::new(5);
-    ///    let m = c.borrow();
     ///
-    ///    let b = c.borrow_mut(); // this causes a panic
-    /// }).join();
+    /// let c = RefCell::new(5);
+    /// let m = c.borrow();
     ///
-    /// assert!(result.is_err());
+    /// let b = c.borrow_mut(); // this causes a panic
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]

src/libcore/char/convert.rs

@@ -278,16 +278,11 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 ///
 /// Passing a large radix, causing a panic:
 ///
-/// ```
-/// use std::thread;
+/// ```should_panic
 /// use std::char;
 ///
-/// let result = thread::spawn(|| {
-///     // this panics
-///     let c = char::from_digit(1, 37);
-/// }).join();
-///
-/// assert!(result.is_err());
+/// // this panics
+/// let c = char::from_digit(1, 37);
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]

src/libcore/char/methods.rs

@@ -229,16 +229,11 @@ pub unsafe fn from_u32_unchecked(i: u32) -> char {
     ///
     /// Passing a large radix, causing a panic:
     ///
-    /// ```
-    /// use std::thread;
+    /// ```should_panic
     /// use std::char;
     ///
-    /// let result = thread::spawn(|| {
-    ///     // this panics
-    ///     let c = char::from_digit(1, 37);
-    /// }).join();
-    ///
-    /// assert!(result.is_err());
+    /// // this panics
+    /// char::from_digit(1, 37);
     /// ```
     #[unstable(feature = "assoc_char_funcs", reason = "recently added", issue = "71763")]
     #[inline]
@@ -282,15 +277,9 @@ pub fn from_digit(num: u32, radix: u32) -> Option<char> {
     ///
     /// Passing a large radix, causing a panic:
     ///
-    /// ```
-    /// use std::thread;
-    ///
-    /// let result = thread::spawn(|| {
-    ///     // this panics
-    ///     '1'.is_digit(37);
-    /// }).join();
-    ///
-    /// assert!(result.is_err());
+    /// ```should_panic
+    /// // this panics
+    /// '1'.is_digit(37);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
@@ -337,14 +326,9 @@ pub fn is_digit(self, radix: u32) -> bool {
     ///
     /// Passing a large radix, causing a panic:
     ///
-    /// ```
-    /// use std::thread;
-    ///
-    /// let result = thread::spawn(|| {
-    ///     '1'.to_digit(37);
-    /// }).join();
-    ///
-    /// assert!(result.is_err());
+    /// ```should_panic
+    /// // this panics
+    /// '1'.to_digit(37);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
@@ -646,17 +630,11 @@ pub fn len_utf16(self) -> usize {
     ///
     /// A buffer that's too small:
     ///
-    /// ```
-    /// use std::thread;
-    ///
-    /// let result = thread::spawn(|| {
-    ///     let mut b = [0; 1];
-    ///
-    ///     // this panics
-    ///    'ß'.encode_utf8(&mut b);
-    /// }).join();
+    /// ```should_panic
+    /// let mut b = [0; 1];
     ///
-    /// assert!(result.is_err());
+    /// // this panics
+    /// 'ß'.encode_utf8(&mut b);
     /// ```
     #[stable(feature = "unicode_encode_char", since = "1.15.0")]
     #[inline]
@@ -687,17 +665,11 @@ pub fn encode_utf8(self, dst: &mut [u8]) -> &mut str {
     ///
     /// A buffer that's too small:
     ///
-    /// ```
-    /// use std::thread;
-    ///
-    /// let result = thread::spawn(|| {
-    ///     let mut b = [0; 1];
-    ///
-    ///     // this panics
-    ///     '𝕊'.encode_utf16(&mut b);
-    /// }).join();
+    /// ```should_panic
+    /// let mut b = [0; 1];
     ///
-    /// assert!(result.is_err());
+    /// // this panics
+    /// '𝕊'.encode_utf16(&mut b);
     /// ```
     #[stable(feature = "unicode_encode_char", since = "1.15.0")]
     #[inline]