Use fully qualified syntax to avoid dyn

library/std/src/io/mod.rs

@@ -2467,7 +2467,7 @@ impl<R: Read> Iterator for Bytes<R> {
     }
 
     fn size_hint(&self) -> (usize, Option<usize>) {
-        (&self.inner as &dyn SizeHint).size_hint()
+        SizeHint::size_hint(&self.inner)
     }
 }
 

library/std/src/io/tests.rs

@@ -1,7 +1,7 @@
 use super::{repeat, Cursor, SeekFrom};
 use crate::cmp::{self, min};
 use crate::io::{self, IoSlice, IoSliceMut};
-use crate::io::{BufRead, Read, Seek, Write};
+use crate::io::{BufRead, BufReader, Read, Seek, Write};
 use crate::ops::Deref;
 
 #[test]
@@ -198,6 +198,26 @@ fn chain_bufread() {
     cmp_bufread(chain1, chain2, &testdata[..]);
 }
 
+#[test]
+fn bufreader_size_hint() {
+    let testdata = b"ABCDEFGHIJKL";
+    let mut buf_reader = BufReader::new(&testdata[..]);
+    assert_eq!(buf_reader.buffer().len(), 0);
+
+    let buffer = buf_reader.fill_buf().unwrap();
+    let buffer_length = buffer.len();
+
+    // Check that size hint matches buffer contents
+    let mut buffered_bytes = buf_reader.bytes();
+    let (lower_bound, _upper_bound) = buffered_bytes.size_hint();
+    assert_eq!(lower_bound, buffer_length);
+
+    // Check that size hint matches buffer contents after advancing
+    buffered_bytes.next().unwrap().unwrap();
+    let (lower_bound, _upper_bound) = buffered_bytes.size_hint();
+    assert_eq!(lower_bound, buffer_length - 1);
+}
+
 #[test]
 fn chain_zero_length_read_is_not_eof() {
     let a = b"A";