Files without contracts cause the Truffle plugin to fail

[frangio]

As reported in the forum, using the Truffle plugin with the following contract that uses operator-filter-registry fails:

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.17;

import "operator-filter-registry/src/DefaultOperatorFilterer.sol";

contract Vox is DefaultOperatorFilterer {}

The error is something like Error: No node with id 645 of type ContractDefinition.

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I traced this issue to this line where the AST for the DefaultOperatorFilterer contract is deleted from the reconstructed compiler output.:

openzeppelin-upgrades/packages/plugin-truffle/src/utils/validations.ts

Line 150 in fc55c0d

delete output.sources[source];

This is roughly due to:

openzeppelin-upgrades/packages/plugin-truffle/src/utils/validations.ts

Line 117 in fc55c0d

// 2. An imported file has only other import statements without an actual contract/library/interface.

Specifically, because of the Constants.sol file which doesn't have a contract in it.

tl;dr: A heuristic we use is failing.

I realize now that we could use a much more direct way to recognize contracts that need to be deleted from the reconstructed compiler output. We should find all contracts that are reachable through imports from files in the user's own contracts directory, and delete anything else.