chore: checkpoint before Python removal

vendor/cipher/src/errors.rs

@@ -0,0 +1,43 @@
+//! Error types.
+
+use core::fmt;
+
+/// This error is returned by the [`StreamCipher`][crate::stream::StreamCipher]
+/// trait methods.
+///
+/// Usually it's used in cases when stream cipher has reached the end
+/// of a keystream, but also can be used if lengths of provided input
+/// and output buffers are not equal.
+#[derive(Copy, Clone, Debug)]
+pub struct StreamCipherError;
+
+impl fmt::Display for StreamCipherError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+        f.write_str("Loop Error")
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+impl std::error::Error for StreamCipherError {}
+
+/// The error type returned when a cipher position can not be represented
+/// by the requested type.
+#[derive(Copy, Clone, Debug)]
+pub struct OverflowError;
+
+impl fmt::Display for OverflowError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+        f.write_str("Overflow Error")
+    }
+}
+
+impl From<OverflowError> for StreamCipherError {
+    fn from(_: OverflowError) -> StreamCipherError {
+        StreamCipherError
+    }
+}
+
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+impl std::error::Error for OverflowError {}