You mean if a transaction contains a message that gets put into a queue or something to be processed at (Begin|End)Block? If so, how would this even be possible to fully simulate?

the simulate would be more of a check of validation then gas consumption if thats what you mean

Hi @tac0turtle, I have some doubts:

What do you mean by nested messages? I saw a proto-definition (but it seems to be only for testing) and the DescriptorProto.
What do you mean by simulate transactions? Is it when a user uses the simulate flag on the client?

What do you mean by nested messages? I saw a proto-definition (but it seems to be only for testing) and the DescriptorProto.

messages can embed other messages in them that will be executed at a later time (gov, etc..). These messages are not simulated so they could fail at a later date when the state machine goes to execute them.

simulation is exposed via an endpoint or cli. here is a link to the code that handles this. Simulating a transaction is used in order to see if a transaction will pass or fail when executing it.

Lmk if you have any more questions, happy to hop on a quick call to explain things if needed as well

What do you mean by nested messages? I saw a proto-definition (but it seems to be only for testing) and the DescriptorProto.

messages can embed other messages in them that will be executed at a later time (gov, etc..). These messages are not simulated so they could fail at a later date when the state machine goes to execute them.

simulation is exposed via an endpoint or cli. here is a link to the code that handles this. Simulating a transaction is used in order to see if a transaction will pass or fail when executing it.

cosmos-sdk/baseapp/abci.go

Lines 988 to 1010 in b4e7df2

	case "simulate":
	txBytes := req.Data
	gInfo, res, err := app.Simulate(txBytes)
	if err != nil {
	return sdkerrors.QueryResult(errorsmod.Wrap(err, "failed to simulate tx"), app.trace)
	}
	simRes := &sdk.SimulationResponse{
	GasInfo: gInfo,
	Result: res,
	}
	bz, err := codec.ProtoMarshalJSON(simRes, app.interfaceRegistry)
	if err != nil {
	return sdkerrors.QueryResult(errorsmod.Wrap(err, "failed to JSON encode simulation response"), app.trace)
	}
	return &abci.ResponseQuery{
	Codespace: sdkerrors.RootCodespace,
	Height: req.Height,
	Value: bz,
	}

.
Lmk if you have any more questions, happy to hop on a quick call to explain things if needed as well

Ok, I understand what the simulation is and the meaning of a nested message (if it's possible I'd like to see an example, I still have doubts about what type the embedded messages have, I'd expect something like a

type msg struct {
 ...
 nested []msg
})

But then, what do you mean by the validation check of the nested message? What validation would be done in the simulation? Could you explain that? If not, I'd be happy to have a quick call

yes, gov submit proposal is a good example:

After taking a look at this, I came to the conclusion that nested messages should be checked in their parent MsgHandler. The handler should always check:

1. can route any nested message.
2. all messages are valid.

In the case of SubmitProposal, messages are not checked deliberately:

Here is the discussion about it. Maybe a cli command to simulate a proposals makes sense as pointed in the discussion.

@tac0turtle