Add std::io::input simple input function.

library/std/src/io/mod.rs

@@ -269,6 +269,8 @@ pub use self::buffered::{BufReader, BufWriter, LineWriter};
 pub use self::cursor::Cursor;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::error::{Error, ErrorKind, Result};
+#[unstable(feature = "io_input", issue = "none")]
+pub use self::stdio::read_line;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::stdio::{stderr, stdin, stdout, Stderr, Stdin, Stdout};
 #[stable(feature = "rust1", since = "1.0.0")]

library/std/src/io/stdio.rs

@@ -7,7 +7,9 @@ use crate::io::prelude::*;
 
 use crate::cell::RefCell;
 use crate::fmt;
-use crate::io::{self, BufReader, Initializer, IoSlice, IoSliceMut, LineWriter};
+use crate::io::{
+    self, BufReader, Error, ErrorKind, Initializer, IoSlice, IoSliceMut, LineWriter, Result, Write,
+};
 use crate::lazy::SyncOnceCell;
 use crate::sync::{Mutex, MutexGuard};
 use crate::sys::stdio;
@@ -873,6 +875,52 @@ impl fmt::Debug for StderrLock<'_> {
     }
 }
 
+/// Reads a [`String`] from [standard input](Stdin). The trailing
+/// newline is stripped. Gives an error on EOF (end of file).
+///
+/// # Note
+///
+/// If you require more explicit control over capturing
+/// user input, see the [`Stdin::read_line`] method.
+///
+/// # Examples
+///
+/// ```no_run
+/// #![feature(io_input)]
+/// use std::io;
+///
+/// fn main() -> io::Result<()> {
+///     print!("Enter name: ");
+///
+///     let name: String = io::read_line()?;
+///
+///     println!("Your name is {}!", name);
+///
+///     Ok(())
+/// }
+/// ```
+#[unstable(
+    feature = "io_input",
+    reason = "this function may be replaced with a more general mechanism",
+    issue = "none"
+)]
+pub fn read_line() -> Result<String> {
+    stdout().flush()?; // print!() does not flush :(
+    let mut input = String::new();
+    match stdin().read_line(&mut input)? {
+        0 => Err(Error::new(ErrorKind::UnexpectedEof, "input reached eof unexpectedly")),
+        _ => {
+            if input.ends_with('\n') {
+                input.pop();
+                if cfg!(windows) && input.ends_with('\r') {
+                    input.pop();
+                }
+            }
+            Ok(input)
+        }
+    }
+}
+
 /// Resets the thread-local stderr handle to the specified writer
 ///
 /// This will replace the current thread's stderr handle, returning the old