Hex string truncated when calling contract function

[vicpon]

I'm using hardhat and ethers 5.6.9. I have a contract with the supportsInterface function.

Test

it("check for mintAndTransfer interface", async () => {
  const { nft: token } = await loadFixture(deployNFTFixture);
  expect(await token.supportsInterface("0x6db15a0f")).to.be.true;
});

The test fails with this error

Error: call revert exception [ See: https://links.ethers.org/v5-errors-CALL_EXCEPTION ] (method="supportsInterface(bytes4)", data="0x", errorArgs=null, errorName=null, errorSignature=null, reason=null, code=CALL_EXCEPTION, version=abi/5.6.4)
      at Logger.makeError (node_modules\@ethersproject\logger\src.ts\index.ts:261:28)
      at Logger.throwError (node_modules\@ethersproject\logger\src.ts\index.ts:273:20)
      at Interface.decodeFunctionResult (node_modules\@ethersproject\abi\src.ts\interface.ts:427:23)
      at Contract.<anonymous> (node_modules\@ethersproject\contracts\src.ts\index.ts:400:44)
      at step (node_modules\@ethersproject\contracts\lib\index.js:48:23)
      at Object.next (node_modules\@ethersproject\contracts\lib\index.js:29:53)
      at fulfilled (node_modules\@ethersproject\contracts\lib\index.js:20:58)

The typechain type generated for that function is

supportsInterface(
  interfaceId: PromiseOrValue<BytesLike>,
  overrides?: CallOverrides
): Promise<boolean>;

The actual contract function:

function supportsInterface(bytes4 interfaceId) public view virtual override(ERC1155Lazy, ERC1155Upgradeable) returns (bool) {
  return this.supportsInterface(interfaceId);
}

Unless I'm reading this wrong, the data seems to be truncated ("0x"). I've tried using the utils in the ethers/lib/utils module to convert to hex with no success. What am I missing?

[zemse]

I see two possible cases for response data to be "0x":

1. The contract reverts without a reason string, because the method supportsInterface(bytes4) is not in the contract bytecode or if method exists then somehow a revert is triggered.
2. If you are sure your contract has the method and it should not revert, then there's might be some issue while loading the fixture and at the moment you're querying, there's no contract bytecode at that address.

To confirm if contract exists you can do:

const code = await hre.ethers.provider.getCode(token.address)
console.log(code) // if this is 0x means no contract code is present

Lmk if the problem persists!

[vicpon]

Thank you for the reply @zemse. I ran your code and do get a value (0x60806040526004361061004e5760003560e01c80633659cfe6146100655780634..., truncated for brevity). Your comment led me to take a closer look at the function implementation and found a bug. Inside the function I was calling this.supportsInterface(interfaceId); instead of super.supportsInterface(interfaceId);. Now it works, thank you!