Slither-flat ignores custom errors defined outside of contract

[markus0x1]

Describe the problem:

Custom errors defined outside of a contract are not imported into the flattened contract.
This is a problem when working with contracts like pr math that define the custom error outside the contract.
Below is an minimum working example showcasing the bug.

Code example to reproduce the issue:

// SPDX-License-Identifier: AGPL-3.0
pragma solidity 0.8.16;

error RevertIt();

contract Example {
  function reverts() external pure {
    revert RevertIt();
  }
}

Version:

0.8.3, 0.9.0

Flattened contract:

pragma solidity 0.8.16;
contract Example {
    function reverts() external pure {
        revert RevertIt();
    }
}

[supernovahs]

@0xalpharush I would like to work on this bug. Could you point me to the code/resources for the same?

[0xalpharush]

@supernovahs You would need to add the top level custom errors here:

slither/slither/tools/flattening/flattening.py

Lines 76 to 79 in 7ea5727

	self._get_source_code_top_level(compilation_unit.structures_top_level)
	self._get_source_code_top_level(compilation_unit.enums_top_level)
	self._get_source_code_top_level(compilation_unit.variables_top_level)
	self._get_source_code_top_level(compilation_unit.functions_top_level)

The compilation unit records the top level custom errors here:
https://github.com/crytic/slither/blob/master/slither/core/compilation_unit.py#L46

[UtsavAnime]

Is there any update on this?