Forward dispatch errors

[forgetso]

Hi,

Dispatch errors are not properly forwarded from typechain-polkadot. The query will pass if the transaction is valid but then the dispatch error is not properly unpacked, resulting in the unhelpful

{"message":"Module"}

Checking polkadot apps shows

system.ExtrinsicFailed
An extrinsic failed. 
dispatchError: SpRuntimeDispatchError
{
  Module: {
    index: 8
    error: 0x06000000
  }
}
type
contracts.ContractNotFound

It seems like there is no way to access the dispatch error from typechain polkadot. I can assign the transaction result to a const but it is never populated as the error is thrown within typechain-polkadot

const txResult = await tasks.contract.tx.myFunction(...myArgs) // txResult is never populated

Instead I have to catch the error from the transaction

    try {
        const txResult = await tasks.contract.tx.myFunction(...myArgs) // txResult is never populated
    } catch (err) {
        logger.error(JSON.stringify(err)) // the module error appears here
    }

Logger output only gives

{"from":"5EjTA28bKSbFPPyMbUjNtArxyqjwq38r1BapVmLZShaqEedV","txHash":"0xa9ad2d8b949c22c1806fa297162305ca5b0735bc4a5c09b6829980214b5af788","blockHash":"0x28e974ee048f13268cb5ad16cd9d478f7e051b0d685e7b270a0a85dd5806f22c","events":[],"error":{"message":"Module"}}

Therefore, you either need to

1. Decode the dispatch error before throwing the error so that the relevant error message is thrown when the user uses try-catch
   or
2. Not throw an error and pass through the raw error information to the user. The user would then have to decode the error with the registry.

// Convert a dispatch error to a readable message
export function getDispatchError(dispatchError: DispatchError): string {
    if (dispatchError.isModule) {
        try {
            const mod = dispatchError.asModule
            const error = dispatchError.registry.findMetaError(mod)
            ...
}

Personally, I prefer option 1 as option 2 is what polkadot-js does and it leaves a lot of complexity to the smart contract developer.

Maybe there is an option 3. which is

3. Decode the error and not throw, simply passing passing back the decoded error in result.error, again allowing the user to decide when to throw.