Vyper

⚠️ A critical security vulnerability has been discovered in this version and we strongly recommend using version [0.3.1](https://github.com/vyperlang/vyper/releases/tag/v0.3.1) or higher. For more information, please see the Security Advisory [GHSA-5824-cm3x-3c38](https://github.com/vyperlang/vyper/security/advisories/GHSA-5824-cm3x-3c38). ⚠️

**Non-breaking changes and improvements:**

- Expose _abi_encode as a user-facing builtin (2401)
- Export the storage layout as a compiler output option (2433)
- Add experimental OVM backend (2416)
- Allow any ABI-encodable type as event arguments (2403)
- Optimize int128 clamping (2411)
- Other docs updates (2405, 2422, 2425)

Fixes:

- Disallow nonreentrant decorator on constructors (2426)
- Fix bounds checks when handling msg.data (2419)
- Allow interfaces in lists, structs and maps (2397)
- Fix trailing newline parse bug (2412)

Special thanks to contributions from skellet0r, sambacha and milancermak for this release!

:warning: A critical security vulnerability has been discovered in this version and we strongly recommend using version [0.3.1](https://github.com/vyperlang/vyper/releases/tag/v0.3.1) or higher. For more information, please see the Security Advisory [GHSA-5824-cm3x-3c38](https://github.com/vyperlang/vyper/security/advisories/GHSA-5824-cm3x-3c38). :warning:

Non-breaking changes and improvements
- Optimization when returning nested tuples ([2392](https://github.com/vyperlang/vyper/pull/2392))

Fixes
- Annotated kwargs for builtins ([2389](https://github.com/vyperlang/vyper/pull/2389))
- Storage slot allocation bug ([2391](https://github.com/vyperlang/vyper/pull/2391))

Non-breaking changes and improvements
- Reduce bytecode by sharing code for clamps ([2387](https://github.com/vyperlang/vyper/pull/2387))

Fixes
- Storage corruption from re-entrancy locks ([2379](https://github.com/vyperlang/vyper/pull/2379))

Non-breaking changes and improvements:

- Add the ``abs`` builtin function ([2356](https://github.com/vyperlang/vyper/pull/2356))
- Streamline the location of arrays within storage ([2361](https://github.com/vyperlang/vyper/pull/2361))

This release fixes a memory corruption bug 2345 that was introduced in the `v0.2.x` series and was not fixed in [VVE-2020-0004](https://github.com/vyperlang/vyper/security/advisories/GHSA-2r3x-4mrv-mcxf). Read about it further in [VVE-2021-0001](https://github.com/vyperlang/vyper/security/advisories/GHSA-22wc-c9wj-6q2v).

Non-breaking changes and improvements:

- Optimize ``calldataload`` (2352)
- Add the ``int256`` signed integer type (2351)
- EIP2929 opcode repricing and Berlin support (2350)
- Add ``msg.data`` environment variable 2343 (2343)
- Full support for Python 3.9 (2233)

This is a patch release to fix a memory corruption bug that was introduced in v0.2.9 (2321) with excessive memory deallocation when releasing internal variables