What The Fuck Was That?

Find out what just happened to your Substrate Transaction by attaching a Rust debugger and re-executing it in a unit test environment. You can either manually create a call or decode and rerun the actual block.

Example

Investigating a recent issue on SE about trapped assets.
First gather the information of the block hash, runtime and runtime verison.
You also need an archive node in order to acquire the correct state at the time of the block. In this example, we run one locally:

wtfwt --rpc ws://127.0.0.1:9944 --block 0x053fdbedde5c2439025e582681711d09b41b93d19dd60db389c7e5f35b3ee597 --runtime-name polkadot --source-repo "polkadot-fellows/runtimes" --source-rev "v1.1.2" --force

This will create a replay directory. You can open this folder now with your IDE and rust-analyezr enabled.
The replay function can be used as playground to either write a normal rust-unit test or inspect / replay the transactions of a specific block.

fn replay(block: Block) {
	Executive::initialize_block(&block.header);

	for extrinsic in block.extrinsics {
		let _ = Executive::apply_extrinsic(extrinsic);
	}

	eprintln!("Events: {:#?}", System::events());

	let _ = Executive::finalize_block();
}

This function acts as a Rust-unit test and can be debugged with normal Rust debugging tools. The #[test] attribute is on its closure function, that provides externalities and the decoded state.

You can run it with:

cargo test --release -- --nocapture