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

library/std/src/io/mod.rs

@@ -266,6 +266,10 @@ 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_prompt", issue = "none")]
+pub use self::stdio::prompt_line;
+#[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

@@ -5,7 +5,9 @@ use crate::io::prelude::*;
 use crate::cell::RefCell;
 use crate::fmt;
 use crate::io::lazy::Lazy;
-use crate::io::{self, BufReader, Initializer, IoSlice, IoSliceMut, LineWriter};
+use crate::io::{self, BufReader, Initializer, IoSlice, IoSliceMut, LineWriter, Write};
+use crate::result;
+use crate::str;
 use crate::sync::{Arc, Mutex, MutexGuard, Once};
 use crate::sys::stdio;
 use crate::sys_common::remutex::{ReentrantMutex, ReentrantMutexGuard};
@@ -903,6 +905,85 @@ impl fmt::Debug for StderrLock<'_> {
     }
 }
 
+/// Similar to the [`prompt_line`] function, but does
+/// not print a prompt.
+///
+/// # 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() {
+///     println!("Enter name: ");
+///
+///     let name: String = io::read_line().unwrap();
+///
+///     println!("Your name is {}!", name);
+/// }
+/// ```
+#[unstable(
+    feature = "io_input",
+    reason = "this function may be replaced with a more general mechanism",
+    issue = "none"
+)]
+pub fn read_line<T: fmt::Display + fmt::Debug>() -> result::Result<T, <T as str::FromStr>::Err>
+where
+    T: str::FromStr,
+    <T as str::FromStr>::Err: fmt::Debug,
+{
+    let mut input = String::new();
+    stdin().read_line(&mut input).expect("failed to read stdin");
+    input.trim_end_matches(&['\n', '\r'][..]).parse::<T>()
+}
+
+/// Prints the given `str` and 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_prompt)]
+/// use std::io;
+///
+/// fn main() {
+///     let name: String = io::prompt_line("Enter name: ").unwrap();
+///
+///     println!("Your name is {}!", name);
+/// }
+/// ```
+#[unstable(
+    feature = "io_input_prompt",
+    reason = "this function may be replaced with a more general mechanism",
+    issue = "none"
+)]
+pub fn prompt_line<T: fmt::Display + fmt::Debug>(
+    prompt: &str,
+) -> result::Result<T, <T as str::FromStr>::Err>
+where
+    T: str::FromStr,
+    <T as str::FromStr>::Err: fmt::Debug,
+{
+    let stdout = stdout();
+    let mut lock = stdout.lock();
+    lock.write_all(prompt.as_bytes()).expect("failed to write whole buffer");
+    lock.flush().expect("failed to flush stdout");
+    let mut input = String::new();
+    stdin().read_line(&mut input).expect("failed to read stdin");
+    input.trim_end_matches(&['\n', '\r'][..]).parse::<T>()
+}
+
 /// Resets the thread-local stderr handle to the specified writer
 ///
 /// This will replace the current thread's stderr handle, returning the old