Replace unstable chars usage

Use private char iterator as done in kkawakam/rustyline#38 while waiting
for stabilisation of the chars method per rust-lang/rust#27802
This removes the need for `#[feature(io)]` letting skim compile on rust
stable.

src/char_iter.rs

@@ -0,0 +1,106 @@
+//! An iterator over the `char`s of a reader.
+//!
+//! A copy of the unstable code from the stdlib's std::io::Read::chars.
+
+use std::error;
+use std::fmt;
+use std::io;
+use std::io::Read;
+use std::str;
+
+pub fn chars<R: Read>(read: R) -> Chars<R> where R: Sized {
+    Chars { inner: read }
+}
+
+// https://tools.ietf.org/html/rfc3629
+static UTF8_CHAR_WIDTH: [u8; 256] = [
+    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x1F
+    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x3F
+    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x5F
+    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
+    1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // 0x7F
+    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 0x9F
+    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 0xBF
+    0,0,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
+    2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, // 0xDF
+    3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3, // 0xEF
+    4,4,4,4,4,0,0,0,0,0,0,0,0,0,0,0, // 0xFF
+];
+
+/// Given a first byte, determine how many bytes are in this UTF-8 character
+#[inline]
+fn utf8_char_width(b: u8) -> usize {
+    return UTF8_CHAR_WIDTH[b as usize] as usize;
+}
+
+pub struct Chars<R> {
+    inner: R,
+}
+
+#[derive(Debug)]
+pub enum CharsError {
+    NotUtf8,
+    Other(io::Error),
+}
+
+impl<R: Read> Iterator for Chars<R> {
+    type Item = Result<char, CharsError>;
+
+    fn next(&mut self) -> Option<Result<char, CharsError>> {
+        let mut buf = [0];
+        let first_byte = match self.inner.read(&mut buf) {
+            Ok(0) => return None,
+            Ok(..) => buf[0],
+            Err(e) => return Some(Err(CharsError::Other(e))),
+        };
+        let width = utf8_char_width(first_byte);
+        if width == 1 { return Some(Ok(first_byte as char)) }
+        if width == 0 { return Some(Err(CharsError::NotUtf8)) }
+        let mut buf = [first_byte, 0, 0, 0];
+        {
+            let mut start = 1;
+            while start < width {
+                match self.inner.read(&mut buf[start..width]) {
+                    Ok(0) => return Some(Err(CharsError::NotUtf8)),
+                    Ok(n) => start += n,
+                    Err(e) => return Some(Err(CharsError::Other(e))),
+                }
+            }
+        }
+        Some(match str::from_utf8(&buf[..width]).ok() {
+            Some(s) => Ok(s.chars().next().unwrap()),
+            None => Err(CharsError::NotUtf8),
+        })
+    }
+}
+
+impl error::Error for CharsError {
+    fn description(&self) -> &str {
+        match *self {
+            CharsError::NotUtf8 => "invalid utf8 encoding",
+            CharsError::Other(ref e) => error::Error::description(e),
+        }
+    }
+    fn cause(&self) -> Option<&error::Error> {
+        match *self {
+            CharsError::NotUtf8 => None,
+            CharsError::Other(ref e) => e.cause(),
+        }
+    }
+}
+
+impl fmt::Display for CharsError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            CharsError::NotUtf8 => {
+                "byte stream did not contain valid utf8".fmt(f)
+            }
+            CharsError::Other(ref e) => e.fmt(f),
+        }
+    }
+}

src/input.rs

@@ -8,6 +8,7 @@ use std::fs::File;
 use std::collections::HashMap;
 use std::collections::VecDeque;
 use std::time::Duration;
+use char_iter;
 
 use event::{Event, EventArg, parse_action};
 
@@ -102,7 +103,7 @@ impl KeyBoard {
     pub fn new(f: File) -> Self {
         let (tx, rx) = channel();
         thread::spawn(move || {
-            for ch in f.chars() {
+            for ch in char_iter::chars(f) {
                 if ch.is_ok() {
                     let _ = tx.send(ch.unwrap());
                 }

src/main.rs

@@ -1,4 +1,3 @@
-#![feature(io)]
 #![cfg_attr(feature="clippy", feature(plugin))]
 #![cfg_attr(feature="clippy", plugin(clippy))]
 extern crate libc;
@@ -19,6 +18,7 @@ mod curses;
 mod query;
 mod ansi;
 mod sender;
+mod char_iter;
 
 use std::thread;
 use std::time::Duration;