New lint: unbuffered_bytes

tests/ui/unbuffered_bytes.rs

@@ -0,0 +1,37 @@
+#![warn(clippy::unbuffered_bytes)]
+
+use std::fs::File;
+use std::io::{BufReader, Cursor, Read, Stdin, stdin};
+use std::net::TcpStream;
+
+fn main() {
+    // File is not buffered, should complain
+    let file = File::open("./bytes.txt").unwrap();
+    file.bytes();
+
+    // TcpStream is not buffered, should complain
+    let tcp_stream: TcpStream = TcpStream::connect("127.0.0.1:80").unwrap();
+    tcp_stream.bytes();
+
+    // BufReader<File> is buffered, should not complain
+    let file = BufReader::new(File::open("./bytes.txt").unwrap());
+    file.bytes();
+
+    // Cursor is buffered, should not complain
+    let cursor = Cursor::new(Vec::new());
+    cursor.bytes();
+
+    // Stdio would acquire the lock for every byte, should complain
+    let s: Stdin = stdin();
+    s.bytes();
+
+    // But when locking stdin, this is fine so should not complain
+    let s: Stdin = stdin();
+    let s = s.lock();
+    s.bytes();
+}
+
+fn use_read<R: Read>(r: R) {
+    // Callers of `use_read` may choose a `R` that is not buffered
+    r.bytes();
+}