[NEVER MERGE] Example of migration to unified failure handling system

[sayon]

This PR demonstrates how to adopt the PoC for the error handling system.

How to play with it

1. Build the CLI from https://github.com/sayon/error-codegen-poc. It will produce an executable: zksync-error-codegen-cli
2. Navigate to the root of era-test-node and execute:

   <path-to-zksync-error-codegen-cli> --definitions root.json --backend rust --verbose  --output=../zksync_error
   

This will generate a crate zksync_error in the directory ../zksync_error with all the errors defined in root.json and errors-era-test-node.json.

A proper way of doing it would be to convert era-test-node to workspace first and place zksync_error in the root, but this is a quick demo.

The root.json file is only for demonstration -- in production, it will be unique for zksync ecosystem and stored in a different, shared repository. The error definitions for era-test-node are located in errors-era-test-node.json.

Changes

NB: This is illustrative: the exact DSL in use can be polished and changed in other ways if you like the approach in general.

1. The first commit migrates the top level errors from anyhow to the unified framework. It wraps everything in a wildcard "TestNodeError" defined in errors-era-test-node.json

Now if we run touch era_test_node.log && chmod 000 era_test_node.log && cargo run we will see:

Error: SerializedError { code: 20001, message: "[core-TestNode-1] Some error in EraTestNode happened: Permission denied (os error 13).", data: Object {"Core": Object {"TestNode": Object {"TestNodeError": Object {"inner": String("Permission denied (os error 13)")}}}} }

2. The second commit introduces a custom error type LogFileCreationError and changes main.rs so that failure of log creation results in this custom error , rather than a wildcard.

Now if we run touch era_test_node.log && chmod 000 era_test_node.log && cargo run we will see:

 Error: SerializedError { code: 21002, message: "[core-TestNode-2] Unable to create log file era_test_node.log: Permission denied (os error 13)", data: Object {"Core": Object {"TestNode": Object {"LogFileCreationError": Object {"inner": String("Permission denied (os error 13)"), "path": String("era_test_node.log")}}}} }

The exact output can be of course tuned to (conditionally) hide the technical details.

[mm-zk]

could genereric_error_msg be a 'macro' -- so that I can direclty replace anyhow! (and dont' have to run the 'format' inside?

[sayon]

Sure! For the PoC we have deliberately tried to not have any macro magic to keep it simple.