From f27ec0f05f2f90ca0291c24a58022b789792c8bf Mon Sep 17 00:00:00 2001
From: Chris Gregory <czipperz@gmail.com>
Date: Sat, 25 May 2019 15:02:35 -0500
Subject: [PATCH 1/2] Add test that impl Seek for BufReader correctly
 invalidates buffer between seeks

---
 src/libstd/io/buffered.rs | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/src/libstd/io/buffered.rs b/src/libstd/io/buffered.rs
index e309f81192cf3..3bdb1e34a8b73 100644
--- a/src/libstd/io/buffered.rs
+++ b/src/libstd/io/buffered.rs
@@ -1162,6 +1162,40 @@ mod tests {
         assert_eq!(reader.get_ref().pos, expected);
     }
 
+    fn test_buffered_reader_seek_underflow_discard_buffer_between_seeks() {
+        // gimmick reader that returns Err after first seek
+        struct ErrAfterFirstSeekReader {
+            first_seek: bool,
+        }
+        impl Read for ErrAfterFirstSeekReader {
+            fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+                for x in &mut *buf {
+                    *x = 0;
+                }
+                Ok(buf.len())
+            }
+        }
+        impl Seek for ErrAfterFirstSeekReader {
+            fn seek(&mut self, _: SeekFrom) -> io::Result<u64> {
+                if self.first_seek {
+                    self.first_seek = false;
+                    Ok(0)
+                } else {
+                    Err(io::Error::new(io::ErrorKind::Other, "oh no!"))
+                }
+            }
+        }
+
+        let mut reader = BufReader::with_capacity(5, ErrAfterFirstSeekReader { first_seek: true });
+        assert_eq!(reader.fill_buf().ok(), Some(&[0, 0, 0, 0, 0][..]));
+
+        // The following seek will require two underlying seeks.  The first will
+        // succeed but the second will fail.  This should still invalidate the
+        // buffer.
+        assert!(reader.seek(SeekFrom::Current(i64::min_value())).is_err());
+        assert_eq!(reader.buffer().len(), 0);
+    }
+
     #[test]
     fn test_buffered_writer() {
         let inner = Vec::new();

From b1ae49cae078d472d9ac55168d7bf5e07ff15a40 Mon Sep 17 00:00:00 2001
From: Chris Gregory <czipperz@gmail.com>
Date: Sat, 25 May 2019 16:37:38 -0500
Subject: [PATCH 2/2] Annotate test with #[test]

---
 src/libstd/io/buffered.rs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/libstd/io/buffered.rs b/src/libstd/io/buffered.rs
index 3bdb1e34a8b73..d0e56acc8fb27 100644
--- a/src/libstd/io/buffered.rs
+++ b/src/libstd/io/buffered.rs
@@ -1162,6 +1162,7 @@ mod tests {
         assert_eq!(reader.get_ref().pos, expected);
     }
 
+    #[test]
     fn test_buffered_reader_seek_underflow_discard_buffer_between_seeks() {
         // gimmick reader that returns Err after first seek
         struct ErrAfterFirstSeekReader {