chore: change prepare and process proposal to be NoOps by default (#1…

…6407)

Co-authored-by: Sergio Mena <sergio@informal.systems>
Co-authored-by: Aleksandr Bezobchuk <alexanderbez@users.noreply.github.com>

baseapp/abci_utils.go

@@ -179,7 +179,7 @@ func NewDefaultProposalHandler(mp mempool.Mempool, txVerifier ProposalTxVerifier
 // FIFO order.
 func (h DefaultProposalHandler) PrepareProposalHandler() sdk.PrepareProposalHandler {
 	return func(ctx sdk.Context, req *abci.RequestPrepareProposal) (*abci.ResponsePrepareProposal, error) {
-		// If the mempool is nil or a no-op mempool, we simply return the transactions
+		// If the mempool is nil or NoOp we simply return the transactions
 		// requested from CometBFT, which, by default, should be in FIFO order.
 		_, isNoOp := h.mempool.(mempool.NoOpMempool)
 		if h.mempool == nil || isNoOp {
@@ -236,6 +236,13 @@ func (h DefaultProposalHandler) PrepareProposalHandler() sdk.PrepareProposalHand
 // is used in both steps, and applications must ensure that this is the case in
 // non-default handlers.
 func (h DefaultProposalHandler) ProcessProposalHandler() sdk.ProcessProposalHandler {
+	// If the mempool is nil or NoOp we simply return ACCEPT,
+	// because PrepareProposal may have included txs that could fail verification.
+	_, isNoOp := h.mempool.(mempool.NoOpMempool)
+	if h.mempool == nil || isNoOp {
+		return NoOpProcessProposal()
+	}
+
 	return func(ctx sdk.Context, req *abci.RequestProcessProposal) (*abci.ResponseProcessProposal, error) {
 		for _, txBytes := range req.Txs {
 			_, err := h.txVerifier.ProcessProposalVerifyTx(txBytes)

docs/docs/building-apps/02-app-mempool.md

@@ -43,7 +43,8 @@ all transactions, it can provide greater control over transaction ordering.
 Allowing the application to handle ordering enables the application to define how
 it would like the block constructed. 
 
-Currently, there is a default `PrepareProposal` implementation provided by the application.
+The Cosmos SDK defines the `DefaultProposalHandler` type, which provides applications with
+`PrepareProposal` and `ProcessProposal` handlers.
 
 ```go reference
 https://github.com/cosmos/cosmos-sdk/blob/v0.47.0-rc1/baseapp/baseapp.go#L868-L916
@@ -116,6 +117,9 @@ A no-op mempool is a mempool where transactions are completely discarded and ign
 When this mempool is used, it assumed that an application will rely on CometBFT's transaction ordering defined in `RequestPrepareProposal`,
 which is FIFO-ordered by default.
 
+> Note: If a NoOp mempool is used, PrepareProposal and ProcessProposal both should be aware of this as
+> PrepareProposal could include transactions that could fail verification in ProcessProposal.
+
 ### Sender Nonce Mempool
 
 The nonce mempool is a mempool that keeps transactions from an sorted by nonce in order to avoid the issues with nonces.