Enum max values can't be used to dimension an array

[gpersoon]

Description

Enum max values can't be used to dimension an array.
An enum max value can be assigned to a constant. But that constant can't be used as an array size.
'Normal' constants can be used to dimension an array.
See example below.

Environment

• Compiler version: 0.8.13
• Target EVM version (as per compiler settings): default
• Framework/IDE (e.g. Truffle or Remix): Remix
• EVM execution environment / backend / blockchain client:
• Operating system: Windows

Steps to Reproduce

//SPDX-License-Identifier: MIT
pragma solidity 0.8.13;

contract test {
    enum ParameterIndexes { P1,P2 }
    uint constant x1 = uint(type(ParameterIndexes).max);
    uint256[x1] params1; // Doesn't compile: Error expected integer literal or constant expression

    uint256[uint(type(ParameterIndexes).max)] params2; // Doesn't compile: Error expected integer literal or constant expression

    uint constant x2 = 7;
    uint256[x2] params3; // Does compile
}

[StrongerXi]

Please see #12832

[StrongerXi]

If there is a strong use case for this, maybe we should consider making ConstantEvaluator more aggressive to handle these cases? i.e., elementary type casting on constant expression, and expression like type(...).max.

[hrkrshnn]

To explain what's going on here, array length should be known during the beginning of the analysis time. However, the expressions type(Enum).max and uint(type(Enum).max) are currently only known towards the end of the code generation. To do this properly, we need better support for compile time constant evaluation. See #3157. However, maybe it is possible to create special cases for uint(...) and type(Enum).max to deal with this easily. Similar examples are type(uint8).max.

[cameel]

I don't think this really needs #3157 to be done properly. It's related but the problem seems to be not in evaluating it (you can already assign type(...).max to a constant and it gets evaluated at compile time) but in the analysis being aware that it's a constant at the point where it's used to size an array.

I think it could be solved in a way similar to #12928, i.e. by just marking the expression as pure. May also need moving the evaluation of type(...).max earlier in the analysis but this seems like something that we should be able to evaluate as soon as we have the enum definition parsed.

[github-actions]

This issue has been marked as stale due to inactivity for the last 90 days.
It will be automatically closed in 7 days.

[github-actions]

Hi everyone! This issue has been automatically closed due to inactivity.
If you think this issue is still relevant in the latest Solidity version and you have something to contribute, feel free to reopen.
However, unless the issue is a concrete proposal that can be implemented, we recommend starting a language discussion on the forum instead.