use _library_ integer constants as fixed-length array sizes

[benediamond]

Description

Integer constants can't be used as the sizes of fixed-length arrays, even when they come from libraries.

Environment

• Compiler version: 0.8.9
• Target EVM version (as per compiler settings): london
• Framework/IDE (e.g. Truffle or Remix): remix, hardhat, etc.
• EVM execution environment / backend / blockchain client:
• Operating system: MacOS

Steps to Reproduce

A.sol:

library A {
    uint256 constant N = 42;
}

B.sol:

import './A.sol';

contract B {
    uint256[A.N] b;
}

leads to

TypeError: Invalid array length, expected integer literal or constant expression.
  --> contracts/B.sol:12:13:
   |
12 |         uint256[A.N] b;
   |                 ^^^

-->

somewhat related original issue, about constants in the same file, now fixed: #716
#1290 is not the same issue; it's about grabbing constants from other contracts which are not libraries. but the workaround suggested there also works here.

[phyBrackets]

I think fixed size array expect compile time constant , but here A.N will be evaluated at runtime .

[chriseth]

A workaround for now would be to move the constant to file level.

This issue could have a duplicate somewhere by the way.

[benediamond]

This issue could have a duplicate somewhere

i looked carefully and didn't find one.

A workaround for now would be to move the constant to file level.

interesting, this move hadn't occurred to me. thanks. feel free to close if you want (though of course i think the "issue" is still open).

[qwerty472123]

@chriseth

For a.sol

uint constant a = 0x12345678;

b.sol

import "./a.sol";

contract Hello {
    uint[a] x;
}

is OK, but c.sol

import * as X from "./a.sol";

contract Hello {
    uint[X.a] x;
}

outputs Error: Invalid array length, expected integer literal or constant expression..

[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.

[KumaCrypto]

Hey, guys! I faced the same problem with compiler version 0.8.23. Do you plan to add support for setting array length using a constant from the library?
The workaround mentioned above didn't work for me.

My simplified case:

library MyLib {
    uint256  internal  constant ARR_LENGTH =  5;
    function getArray()  internal  pure  returns(uint256[ARR_LENGTH] memory arr) {
        return arr;
    }
} 

contract MyContract {
    function useArrayFromLib()  external  {
        uint256[MyLib.ARR_LENGTH] memory arr = MyLib.getArray();
    }
}