Rollup merge of #134593 - kornelski:less-unwrap, r=jhpratt

Less unwrap() in documentation

I think the common use of `.unwrap()` in examples makes it overrepresented, looking like a more typical way of error handling than it really is in real programs.

Therefore, this PR changes a bunch of examples to use different error handling methods, primarily the `?` operator. Additionally, `unwrap()` docs warn that it might abort the program.

library/alloc/src/collections/binary_heap/mod.rs

@@ -531,8 +531,7 @@ impl<T: Ord, A: Allocator> BinaryHeap<T, A> {
     /// heap.push(1);
     /// heap.push(5);
     /// heap.push(2);
-    /// {
-    ///     let mut val = heap.peek_mut().unwrap();
+    /// if let Some(mut val) = heap.peek_mut() {
     ///     *val = 0;
     /// }
     /// assert_eq!(heap.peek(), Some(&2));

library/core/src/cell/once.rs

@@ -262,7 +262,9 @@ impl<T> OnceCell<T> {
     ///
     /// let value = cell.get_mut_or_try_init(|| "1234".parse());
     /// assert_eq!(value, Ok(&mut 1234));
-    /// *value.unwrap() += 2;
+    ///
+    /// let Ok(value) = value else { return; };
+    /// *value += 2;
     /// assert_eq!(cell.get(), Some(&1236))
     /// ```
     #[unstable(feature = "once_cell_get_mut", issue = "121641")]
@@ -304,8 +306,8 @@ impl<T> OnceCell<T> {
     /// assert_eq!(cell.into_inner(), None);
     ///
     /// let cell = OnceCell::new();
-    /// cell.set("hello".to_string()).unwrap();
-    /// assert_eq!(cell.into_inner(), Some("hello".to_string()));
+    /// let _ = cell.set("hello".to_owned());
+    /// assert_eq!(cell.into_inner(), Some("hello".to_owned()));
     /// ```
     #[inline]
     #[stable(feature = "once_cell", since = "1.70.0")]
@@ -332,8 +334,8 @@ impl<T> OnceCell<T> {
     /// assert_eq!(cell.take(), None);
     ///
     /// let mut cell = OnceCell::new();
-    /// cell.set("hello".to_string()).unwrap();
-    /// assert_eq!(cell.take(), Some("hello".to_string()));
+    /// let _ = cell.set("hello".to_owned());
+    /// assert_eq!(cell.take(), Some("hello".to_owned()));
     /// assert_eq!(cell.get(), None);
     /// ```
     #[inline]

library/core/src/fmt/mod.rs

@@ -152,8 +152,9 @@ pub trait Write {
     /// }
     ///
     /// let mut buf = String::new();
-    /// writer(&mut buf, "hola").unwrap();
+    /// writer(&mut buf, "hola")?;
     /// assert_eq!(&buf, "hola");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     fn write_str(&mut self, s: &str) -> Result;
@@ -179,9 +180,10 @@ pub trait Write {
     /// }
     ///
     /// let mut buf = String::new();
-    /// writer(&mut buf, 'a').unwrap();
-    /// writer(&mut buf, 'b').unwrap();
+    /// writer(&mut buf, 'a')?;
+    /// writer(&mut buf, 'b')?;
     /// assert_eq!(&buf, "ab");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "fmt_write_char", since = "1.1.0")]
     fn write_char(&mut self, c: char) -> Result {
@@ -208,8 +210,9 @@ pub trait Write {
     /// }
     ///
     /// let mut buf = String::new();
-    /// writer(&mut buf, "world").unwrap();
+    /// writer(&mut buf, "world")?;
     /// assert_eq!(&buf, "world");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     fn write_fmt(&mut self, args: Arguments<'_>) -> Result {

library/core/src/iter/sources/once.rs

@@ -34,7 +34,7 @@ use crate::iter::{FusedIterator, TrustedLen};
 /// use std::fs;
 /// use std::path::PathBuf;
 ///
-/// let dirs = fs::read_dir(".foo").unwrap();
+/// let dirs = fs::read_dir(".foo")?;
 ///
 /// // we need to convert from an iterator of DirEntry-s to an iterator of
 /// // PathBufs, so we use map
@@ -50,6 +50,7 @@ use crate::iter::{FusedIterator, TrustedLen};
 /// for f in files {
 ///     println!("{f:?}");
 /// }
+/// # std::io::Result::Ok(())
 /// ```
 #[stable(feature = "iter_once", since = "1.2.0")]
 pub fn once<T>(value: T) -> Once<T> {

library/core/src/iter/traits/iterator.rs

@@ -2564,7 +2564,7 @@ pub trait Iterator {
     /// # Example
     ///
     /// ```
-    /// let reduced: i32 = (1..10).reduce(|acc, e| acc + e).unwrap();
+    /// let reduced: i32 = (1..10).reduce(|acc, e| acc + e).unwrap_or(0);
     /// assert_eq!(reduced, 45);
     ///
     /// // Which is equivalent to doing it with `fold`:
@@ -3087,7 +3087,7 @@ pub trait Iterator {
     ///     [2.4, f32::NAN, 1.3]
     ///         .into_iter()
     ///         .reduce(f32::max)
-    ///         .unwrap(),
+    ///         .unwrap_or(0.),
     ///     2.4
     /// );
     /// ```
@@ -3123,7 +3123,7 @@ pub trait Iterator {
     ///     [2.4, f32::NAN, 1.3]
     ///         .into_iter()
     ///         .reduce(f32::min)
-    ///         .unwrap(),
+    ///         .unwrap_or(0.),
     ///     1.3
     /// );
     /// ```

library/core/src/option.rs

@@ -937,10 +937,16 @@ impl<T> Option<T> {
     /// Returns the contained [`Some`] value, consuming the `self` value.
     ///
     /// Because this function may panic, its use is generally discouraged.
+    /// Panics are meant for unrecoverable errors, and
+    /// [may abort the entire program][panic-abort].
+    ///
     /// Instead, prefer to use pattern matching and handle the [`None`]
     /// case explicitly, or call [`unwrap_or`], [`unwrap_or_else`], or
-    /// [`unwrap_or_default`].
+    /// [`unwrap_or_default`]. In functions returning `Option`, you can use
+    /// [the `?` (try) operator][try-option].
     ///
+    /// [panic-abort]: https://doc.rust-lang.org/book/ch09-01-unrecoverable-errors-with-panic.html
+    /// [try-option]: https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#where-the--operator-can-be-used
     /// [`unwrap_or`]: Option::unwrap_or
     /// [`unwrap_or_else`]: Option::unwrap_or_else
     /// [`unwrap_or_default`]: Option::unwrap_or_default

library/core/src/ptr/const_ptr.rs

@@ -502,11 +502,12 @@ impl<T: ?Sized> *const T {
     /// let mut out = String::new();
     /// while ptr != end_rounded_up {
     ///     unsafe {
-    ///         write!(&mut out, "{}, ", *ptr).unwrap();
+    ///         write!(&mut out, "{}, ", *ptr)?;
     ///     }
     ///     ptr = ptr.wrapping_offset(step);
     /// }
     /// assert_eq!(out.as_str(), "1, 3, 5, ");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "ptr_wrapping_offset", since = "1.16.0")]
     #[must_use = "returns a new pointer rather than modifying its argument"]
@@ -1125,11 +1126,12 @@ impl<T: ?Sized> *const T {
     /// let mut out = String::new();
     /// while ptr != end_rounded_up {
     ///     unsafe {
-    ///         write!(&mut out, "{}, ", *ptr).unwrap();
+    ///         write!(&mut out, "{}, ", *ptr)?;
     ///     }
     ///     ptr = ptr.wrapping_add(step);
     /// }
     /// assert_eq!(out, "1, 3, 5, ");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "pointer_methods", since = "1.26.0")]
     #[must_use = "returns a new pointer rather than modifying its argument"]
@@ -1203,11 +1205,12 @@ impl<T: ?Sized> *const T {
     /// let mut out = String::new();
     /// while ptr != start_rounded_down {
     ///     unsafe {
-    ///         write!(&mut out, "{}, ", *ptr).unwrap();
+    ///         write!(&mut out, "{}, ", *ptr)?;
     ///     }
     ///     ptr = ptr.wrapping_sub(step);
     /// }
     /// assert_eq!(out, "5, 3, 1, ");
+    /// # std::fmt::Result::Ok(())
     /// ```
     #[stable(feature = "pointer_methods", since = "1.26.0")]
     #[must_use = "returns a new pointer rather than modifying its argument"]

library/core/src/result.rs

@@ -1065,10 +1065,15 @@ impl<T, E> Result<T, E> {
     /// Returns the contained [`Ok`] value, consuming the `self` value.
     ///
     /// Because this function may panic, its use is generally discouraged.
-    /// Instead, prefer to use pattern matching and handle the [`Err`]
-    /// case explicitly, or call [`unwrap_or`], [`unwrap_or_else`], or
-    /// [`unwrap_or_default`].
+    /// Panics are meant for unrecoverable errors, and
+    /// [may abort the entire program][panic-abort].
     ///
+    /// Instead, prefer to use [the `?` (try) operator][try-operator], or pattern matching
+    /// to handle the [`Err`] case explicitly, or call [`unwrap_or`],
+    /// [`unwrap_or_else`], or [`unwrap_or_default`].
+    ///
+    /// [panic-abort]: https://doc.rust-lang.org/book/ch09-01-unrecoverable-errors-with-panic.html
+    /// [try-operator]: https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator
     /// [`unwrap_or`]: Result::unwrap_or
     /// [`unwrap_or_else`]: Result::unwrap_or_else
     /// [`unwrap_or_default`]: Result::unwrap_or_default

library/core/src/str/converts.rs

@@ -47,10 +47,11 @@ use crate::{mem, ptr};
 /// // some bytes, in a vector
 /// let sparkle_heart = vec![240, 159, 146, 150];
 ///
-/// // We know these bytes are valid, so just use `unwrap()`.
-/// let sparkle_heart = str::from_utf8(&sparkle_heart).unwrap();
+/// // We can use the ? (try) operator to check if the bytes are valid
+/// let sparkle_heart = str::from_utf8(&sparkle_heart)?;
 ///
 /// assert_eq!("💖", sparkle_heart);
+/// # Ok::<_, str::Utf8Error>(())
 /// ```
 ///
 /// Incorrect bytes:

library/core/src/sync/atomic.rs

@@ -86,7 +86,7 @@
 //!     // This is fine: `join` synchronizes the code in a way such that the atomic
 //!     // store happens-before the non-atomic write.
 //!     let handle = s.spawn(|| atomic.store(1, Ordering::Relaxed)); // atomic store
-//!     handle.join().unwrap(); // synchronize
+//!     handle.join().expect("thread won't panic"); // synchronize
 //!     s.spawn(|| unsafe { atomic.as_ptr().write(2) }); // non-atomic write
 //! });
 //!
@@ -103,7 +103,7 @@
 //!     // This is fine: `join` synchronizes the code in a way such that
 //!     // the 1-byte store happens-before the 2-byte store.
 //!     let handle = s.spawn(|| atomic.store(1, Ordering::Relaxed));
-//!     handle.join().unwrap();
+//!     handle.join().expect("thread won't panic");
 //!     s.spawn(|| unsafe {
 //!         let differently_sized = transmute::<&AtomicU16, &AtomicU8>(&atomic);
 //!         differently_sized.store(2, Ordering::Relaxed);

library/std/src/io/mod.rs

@@ -1083,7 +1083,7 @@ pub trait Read {
     ///     let f = BufReader::new(File::open("foo.txt")?);
     ///
     ///     for byte in f.bytes() {
-    ///         println!("{}", byte.unwrap());
+    ///         println!("{}", byte?);
     ///     }
     ///     Ok(())
     /// }
@@ -1995,15 +1995,16 @@ pub trait Seek {
     ///     .write(true)
     ///     .read(true)
     ///     .create(true)
-    ///     .open("foo.txt").unwrap();
+    ///     .open("foo.txt")?;
     ///
     /// let hello = "Hello!\n";
-    /// write!(f, "{hello}").unwrap();
-    /// f.rewind().unwrap();
+    /// write!(f, "{hello}")?;
+    /// f.rewind()?;
     ///
     /// let mut buf = String::new();
-    /// f.read_to_string(&mut buf).unwrap();
+    /// f.read_to_string(&mut buf)?;
     /// assert_eq!(&buf, hello);
+    /// # std::io::Result::Ok(())
     /// ```
     #[stable(feature = "seek_rewind", since = "1.55.0")]
     fn rewind(&mut self) -> Result<()> {
@@ -2212,8 +2213,9 @@ fn skip_until<R: BufRead + ?Sized>(r: &mut R, delim: u8) -> Result<usize> {
 ///
 /// let stdin = io::stdin();
 /// for line in stdin.lock().lines() {
-///     println!("{}", line.unwrap());
+///     println!("{}", line?);
 /// }
+/// # std::io::Result::Ok(())
 /// ```
 ///
 /// If you have something that implements [`Read`], you can use the [`BufReader`
@@ -2236,7 +2238,8 @@ fn skip_until<R: BufRead + ?Sized>(r: &mut R, delim: u8) -> Result<usize> {
 ///     let f = BufReader::new(f);
 ///
 ///     for line in f.lines() {
-///         println!("{}", line.unwrap());
+///         let line = line?;
+///         println!("{line}");
 ///     }
 ///
 ///     Ok(())
@@ -2274,7 +2277,7 @@ pub trait BufRead: Read {
     /// let stdin = io::stdin();
     /// let mut stdin = stdin.lock();
     ///
-    /// let buffer = stdin.fill_buf().unwrap();
+    /// let buffer = stdin.fill_buf()?;
     ///
     /// // work with buffer
     /// println!("{buffer:?}");
@@ -2282,6 +2285,7 @@ pub trait BufRead: Read {
     /// // ensure the bytes we worked with aren't returned again later
     /// let length = buffer.len();
     /// stdin.consume(length);
+    /// # std::io::Result::Ok(())
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     fn fill_buf(&mut self) -> Result<&[u8]>;
@@ -2327,12 +2331,13 @@ pub trait BufRead: Read {
     /// let stdin = io::stdin();
     /// let mut stdin = stdin.lock();
     ///
-    /// while stdin.has_data_left().unwrap() {
+    /// while stdin.has_data_left()? {
     ///     let mut line = String::new();
-    ///     stdin.read_line(&mut line).unwrap();
+    ///     stdin.read_line(&mut line)?;
     ///     // work with line
     ///     println!("{line:?}");
     /// }
+    /// # std::io::Result::Ok(())
     /// ```
     #[unstable(feature = "buf_read_has_data_left", reason = "recently added", issue = "86423")]
     fn has_data_left(&mut self) -> Result<bool> {

library/std/src/process.rs

@@ -224,7 +224,7 @@ pub struct Child {
     /// has been captured. You might find it helpful to do
     ///
     /// ```ignore (incomplete)
-    /// let stdin = child.stdin.take().unwrap();
+    /// let stdin = child.stdin.take().expect("handle present");
     /// ```
     ///
     /// to avoid partially moving the `child` and thus blocking yourself from calling
@@ -236,7 +236,7 @@ pub struct Child {
     /// has been captured. You might find it helpful to do
     ///
     /// ```ignore (incomplete)
-    /// let stdout = child.stdout.take().unwrap();
+    /// let stdout = child.stdout.take().expect("handle present");
     /// ```
     ///
     /// to avoid partially moving the `child` and thus blocking yourself from calling
@@ -248,7 +248,7 @@ pub struct Child {
     /// has been captured. You might find it helpful to do
     ///
     /// ```ignore (incomplete)
-    /// let stderr = child.stderr.take().unwrap();
+    /// let stderr = child.stderr.take().expect("handle present");
     /// ```
     ///
     /// to avoid partially moving the `child` and thus blocking yourself from calling
@@ -1052,14 +1052,14 @@ impl Command {
     /// use std::io::{self, Write};
     /// let output = Command::new("/bin/cat")
     ///     .arg("file.txt")
-    ///     .output()
-    ///     .expect("failed to execute process");
+    ///     .output()?;
     ///
     /// println!("status: {}", output.status);
-    /// io::stdout().write_all(&output.stdout).unwrap();
-    /// io::stderr().write_all(&output.stderr).unwrap();
+    /// io::stdout().write_all(&output.stdout)?;
+    /// io::stderr().write_all(&output.stderr)?;
     ///
     /// assert!(output.status.success());
+    /// # io::Result::Ok(())
     /// ```
     #[stable(feature = "process", since = "1.0.0")]
     pub fn output(&mut self) -> io::Result<Output> {
@@ -1391,11 +1391,11 @@ impl Stdio {
     /// let output = Command::new("rev")
     ///     .stdin(Stdio::inherit())
     ///     .stdout(Stdio::piped())
-    ///     .output()
-    ///     .expect("Failed to execute command");
+    ///     .output()?;
     ///
     /// print!("You piped in the reverse of: ");
-    /// io::stdout().write_all(&output.stdout).unwrap();
+    /// io::stdout().write_all(&output.stdout)?;
+    /// # io::Result::Ok(())
     /// ```
     #[must_use]
     #[stable(feature = "process", since = "1.0.0")]
@@ -1575,14 +1575,14 @@ impl From<fs::File> for Stdio {
     /// use std::process::Command;
     ///
     /// // With the `foo.txt` file containing "Hello, world!"
-    /// let file = File::open("foo.txt").unwrap();
+    /// let file = File::open("foo.txt")?;
     ///
     /// let reverse = Command::new("rev")
     ///     .stdin(file)  // Implicit File conversion into a Stdio
-    ///     .output()
-    ///     .expect("failed reverse command");
+    ///     .output()?;
     ///
     /// assert_eq!(reverse.stdout, b"!dlrow ,olleH");
+    /// # std::io::Result::Ok(())
     /// ```
     fn from(file: fs::File) -> Stdio {
         Stdio::from_inner(file.into_inner().into())
@@ -2179,7 +2179,7 @@ impl Child {
     /// ```no_run
     /// use std::process::Command;
     ///
-    /// let mut child = Command::new("ls").spawn().unwrap();
+    /// let mut child = Command::new("ls").spawn()?;
     ///
     /// match child.try_wait() {
     ///     Ok(Some(status)) => println!("exited with: {status}"),
@@ -2190,6 +2190,7 @@ impl Child {
     ///     }
     ///     Err(e) => println!("error attempting to wait: {e}"),
     /// }
+    /// # std::io::Result::Ok(())
     /// ```
     #[stable(feature = "process_try_wait", since = "1.18.0")]
     pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {