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

src/libstd/io/mod.rs

@@ -278,6 +278,10 @@ 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 = "input", issue = "none")]
+pub use self::stdio::input;
+#[unstable(feature = "prompt", issue = "none")]
+pub use self::stdio::prompt;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::stdio::{stderr, stdin, stdout, Stderr, Stdin, Stdout};
 #[stable(feature = "rust1", since = "1.0.0")]

src/libstd/io/stdio.rs

@@ -5,7 +5,7 @@ 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, Result, Write};
 use crate::sync::{Arc, Mutex, MutexGuard, Once};
 use crate::sys::stdio;
 use crate::sys_common::remutex::{ReentrantMutex, ReentrantMutexGuard};
@@ -872,6 +872,95 @@ impl fmt::Debug for StderrLock<'_> {
     }
 }
 
+/// Equivalent to the [`input`] method except that a prompt
+/// is printed before capturing input. This function returns
+/// either success ([`Ok`]) or failure ([`Err`]) containing
+/// the input. See the [`std::result`] module documentation
+/// for details.
+///
+/// # Note
+///
+/// This function is not the recommended solution to get user input, it should
+/// only be used for simple actions. If you require more explicit control over
+/// getting user input, see the [`Stdin::read_line`] method.
+///
+/// # Panics
+///
+/// This function currently panics if it does not receive input,
+/// or when input is empty (end of file / `ctrl + d`).
+///
+/// # Examples
+///
+/// ```no_run
+/// #![feature(prompt)]
+/// use std::io::prompt;
+///
+/// fn main() {
+///     let name = prompt("Enter name: ").expect("input failed!");
+///
+///     println!("Your name is {}!", name);
+/// }
+/// ```
+#[unstable(
+    feature = "prompt",
+    reason = "this function may be replaced with a \
+                     more general mechanism",
+    issue = "none"
+)]
+pub fn prompt(prompt: &str) -> Result<String> {
+    stdout().write(prompt.as_bytes())?;
+    input()
+}
+
+/// Constructs a new handle to the standard input of the current
+/// process, locks this handle and reads a line of input, returning
+/// either success ([`Ok`]) or failure ([`Err`]) containing the input.
+/// See the [`std::result`] module documentation for details. For
+/// automatic prompt handling, see the [`prompt`] method.
+///
+/// If you need more explicit control over
+/// locking, see the [`Stdin::lock`] and [`Stdout::lock`] methods.
+///
+/// # Note
+///
+/// This function is not the recommended solution to get user input, it should
+/// only be used for simple actions. If you require more explicit control over
+/// getting user input, see the [`Stdin::read_line`] method.
+///
+/// # Panics
+///
+/// This function currently panics if it does not receive input
+/// or when input is empty (end of file / `ctrl + d`).
+///
+/// # Examples
+///
+/// ```no_run
+/// #![feature(input)]
+/// use std::io::input;
+///
+/// fn main() {
+///     print!("Enter name: ");
+///
+///     let name = input().expect("input failed!");
+///
+///     println!("Your name is {}!", name);
+/// }
+/// ```
+#[unstable(
+    feature = "input",
+    reason = "this function may be replaced with a \
+                     more general mechanism",
+    issue = "none"
+)]
+pub fn input() -> Result<String> {
+    stdout().flush()?;
+    let mut input = String::new();
+    match stdin().read_line(&mut input)? {
+        0 => panic!("unexpected end of file"),
+        _ => Ok(String::from(input.trim_end_matches(&['\n', '\r'][..]))),
+    }
+}
+
 /// Resets the thread-local stderr handle to the specified writer
 ///
 /// This will replace the current thread's stderr handle, returning the old

src/libstd/lib.rs

@@ -274,6 +274,7 @@
 #![feature(global_asm)]
 #![feature(hash_raw_entry)]
 #![feature(hashmap_internals)]
+#![feature(input)]
 #![feature(int_error_internals)]
 #![feature(int_error_matching)]
 #![feature(into_future)]
@@ -296,6 +297,7 @@
 #![feature(panic_internals)]
 #![feature(panic_unwind)]
 #![feature(prelude_import)]
+#![feature(prompt)]
 #![feature(ptr_internals)]
 #![feature(raw)]
 #![feature(raw_ref_macros)]