Unexpected storage layout caused by interfaces

[cyraxred]

Description

Addition of an interface causes reordering of fields in the storage layout.

Environment

• Compiler version: reproduced on 0.8.0, 0.8.4, 0.8.10. 0.8.15
• Framework/IDE (e.g. Truffle or Remix): Remix, VisualStudio

Steps to Reproduce

Compiling of the code below gives following storage layouts:

• V1: p11, p12
• V2: p21, p11, p12, p22

Expected layout is:

• V1: p11, p12
• V2: p11, p12, p21, p22

When ITest is removed from P22, then the layout is generated as expected.
This effect depends on position of interfaces on the inheritance list, especially for contracts with complex composition.

interface ITest {}

contract P11 is ITest {
    uint8 public p11 = 11;
}

contract P12 is P11 {
    uint8 public p12 = 12;
}

contract V1 is P12 {}

contract P21 {
    uint8 public p21 = 21;
}

contract P22 is P21, ITest {
    uint8 public p22 = 22;
}

contract V2 is V1, P22 {}

[cyraxred]

A simple demo
https://github.com/cyraxred/solidity-layout-bug

[ekpyron]

The layout of storage in the presence of inheritance is determined by the C3 linearization of the inheritance graph.
Adding the interface changes the C3 linearization, so the change in the storage layout is expected, conforms to the current specification and is in that sense not a bug.

That being said, I'm actually wondering, whether interfaces should be exempt from being treated the same as contracts in the C3 linearization - out of my head, it seems to me that this would be possible and might actually be beneficial. This would be a gravely breaking change, though, so at least for the time being, the change in storage layout is expected and this behaviour cannot be changed in the short term...

[cyraxred]

yeah, ideally, interfaces should be exempt from the linearization

[Elyx0]

Is there any tool to preview the solidity C3 output of a given contract?

[montyly]

@Elyx0 : you can use slither's inheritance graph: https://github.com/crytic/slither/wiki/Printer-documentation#inheritance-graph

slither file.sol --print inheritance-graph

[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.