TryReserveError to ErrorKind::OutOfMemory

Author: kornelski

library/std/src/io/error.rs

@@ -83,6 +83,18 @@ impl From<alloc::ffi::NulError> for Error {
     }
 }
 
+#[stable(feature = "io_error_from_try_reserve", since = "CURRENT_RUSTC_VERSION")]
+impl From<alloc::collections::TryReserveError> for Error {
+    /// Converts `TryReserveError` to an error with [`ErrorKind::OutOfMemory`].
+    ///
+    /// `TryReserveError` won't be available as the error `source()`,
+    /// but this may change in the future.
+    fn from(_: alloc::collections::TryReserveError) -> Error {
+        // ErrorData::Custom allocates, which isn't great for handling OOM errors.
+        ErrorKind::OutOfMemory.into()
+    }
+}
+
 // Only derive debug in tests, to make sure it
 // doesn't accidentally get printed.
 #[cfg_attr(test, derive(Debug))]

library/std/src/io/tests.rs

@@ -692,3 +692,13 @@ fn read_buf_full_read() {
 
     assert_eq!(BufReader::new(FullRead).fill_buf().unwrap().len(), DEFAULT_BUF_SIZE);
 }
+
+#[test]
+// 64-bit only to be sure the allocator will fail fast on an impossible to satsify size
+#[cfg(target_pointer_width = "64")]
+fn try_oom_error() {
+    let mut v = Vec::<u8>::new();
+    let reserve_err = v.try_reserve(isize::MAX as usize - 1).unwrap_err();
+    let io_err = io::Error::from(reserve_err);
+    assert_eq!(io::ErrorKind::OutOfMemory, io_err.kind());
+}