Meta Issue: Planned breaking changes for new major (5.0)

[Amxx]

Here is a list of breaking changes that we would like to include in the next major release. Timming for this release is not yet known.

• Solidity 0.8.4 Custom Errors #2839
• [5.0.0 Breaking change] Using user defined value type for timers #2962
  Fix data packing with nested structures smaller than one slot. In particular, the Governor.ProposalCore structure is not effectively packed. We might remove the Timers struct in exchange for alias to uint64.
• Include address(this) when computing Governor proposal ids #3926
• Use diamond storage instead of gaps in upgradeable contracts #2964
• Don't rename interfaces IWhatever -> IWhateverUpgradeable #3928
  • Make some contract libraries (ERC1967)
  • Make some storage values constant (see 712)
• Make ERC20Votes independent from ERC20Permit #3816
• New abstractions for better nonce system #3927
• Replace abi.encodeWithSelector by abi.encodeCall #3693

[frangio]

We should break this up into multiple issues except those that should be implemented and reviewed together.

We might just need the milestone to track these items instead of the meta issue.

[frangio]

Most of these items have their own issues by now so I will close this issue.

The missing ones are:

• Make some contract libraries (ERC1967)

We can't make ERC1967Upgrade into a library because it needs to emit events. I don't know if there are others like this.

• Make some storage values constant (see 712)

Not sure exactly what this means. We do have #2538 and #2638, none of those are about EIP712.