staking: Don't emit zero-amount staking events

If fees were set to 0, staking events related to the fee accumulator
would still get emitted with zero amounts, which is pointless.

This fix affects only events related to the internal fee accumulator
and common pool accounts, manual transfers with 0 as the amount will
still get emitted.

go/consensus/tendermint/apps/staking/fees.go

@@ -63,7 +63,7 @@ func (app *stakingApplication) disburseFeesP(
 
 	// Pay the proposer.
 	feeProposerAmt := totalFees.Clone()
-	if proposerEntity != nil {
+	if proposerEntity != nil && !feeProposerAmt.IsZero() {
 		acct, err := stakeState.Account(ctx, *proposerEntity)
 		if err != nil {
 			return fmt.Errorf("failed to fetch proposer account: %w", err)

go/consensus/tendermint/apps/staking/state/gas.go

@@ -98,13 +98,15 @@ func AuthenticateAndPayFees(
 		return fmt.Errorf("failed to set account: %w", err)
 	}
 
-	// Emit transfer event.
-	ev := cbor.Marshal(&staking.TransferEvent{
-		From:   id,
-		To:     staking.FeeAccumulatorAccountID,
-		Tokens: fee.Amount,
-	})
-	ctx.EmitEvent(abciAPI.NewEventBuilder(AppName).Attribute(KeyTransfer, ev))
+	// Emit transfer event if fee is non-zero.
+	if !fee.Amount.IsZero() {
+		ev := cbor.Marshal(&staking.TransferEvent{
+			From:   id,
+			To:     staking.FeeAccumulatorAccountID,
+			Tokens: fee.Amount,
+		})
+		ctx.EmitEvent(abciAPI.NewEventBuilder(AppName).Attribute(KeyTransfer, ev))
+	}
 
 	// Configure gas accountant on the context.
 	ctx.SetGasAccountant(abciAPI.NewCompositeGasAccountant(

go/staking/tests/tester.go

@@ -181,20 +181,18 @@ func testTransfer(t *testing.T, state *stakingTestsState, backend api.Backend, c
 	err = consensusAPI.SignAndSubmitTx(context.Background(), consensus, srcSigner, tx)
 	require.NoError(err, "Transfer")
 
-	var gotCommon bool
-	var gotFeeAcc bool
 	var gotTransfer bool
 
 TransferWaitLoop:
 	for {
 		select {
 		case ev := <-ch:
 			if ev.From.Equal(api.CommonPoolAccountID) || ev.To.Equal(api.CommonPoolAccountID) {
-				gotCommon = true
+				require.False(ev.Tokens.IsZero(), "CommonPool xfer: amount should be non-zero")
 				continue
 			}
 			if ev.From.Equal(api.FeeAccumulatorAccountID) || ev.To.Equal(api.FeeAccumulatorAccountID) {
-				gotFeeAcc = true
+				require.False(ev.Tokens.IsZero(), "FeeAccumulator xfer: amount should be non-zero")
 				continue
 			}
 
@@ -218,16 +216,14 @@ TransferWaitLoop:
 				require.True(gotTransfer, "GetEvents should return transfer event")
 			}
 
-			if (gotCommon || gotFeeAcc) && gotTransfer {
+			if gotTransfer {
 				break TransferWaitLoop
 			}
 		case <-time.After(recvTimeout):
 			t.Fatalf("failed to receive transfer event")
 		}
 	}
 
-	require.True(gotCommon || gotFeeAcc, "WatchTransfers should also return transfers related to the common pool and/or the fee accumulator")
-
 	_ = srcAcc.General.Balance.Sub(&xfer.Tokens)
 	newSrcAcc, err := backend.AccountInfo(context.Background(), &api.OwnerQuery{Owner: SrcID, Height: consensusAPI.HeightLatest})
 	require.NoError(err, "src: AccountInfo - after")
@@ -267,8 +263,6 @@ func testTransferWatchEvents(t *testing.T, state *stakingTestsState, backend api
 	err = consensusAPI.SignAndSubmitTx(context.Background(), consensus, srcSigner, tx)
 	require.NoError(err, "SignAndSubmitTx")
 
-	var gotCommon bool
-	var gotFeeAcc bool
 	var gotTransfer bool
 
 TransferWaitLoop:
@@ -282,14 +276,15 @@ TransferWaitLoop:
 
 			from := ev.TransferEvent.From
 			to := ev.TransferEvent.To
+			tokens := ev.TransferEvent.Tokens
 
 			// We should also get some traffic to/from the common pool and fee accumulator.
 			if from.Equal(api.CommonPoolAccountID) || to.Equal(api.CommonPoolAccountID) {
-				gotCommon = true
+				require.False(tokens.IsZero(), "CommonPool xfer: amount should be non-zero")
 				continue
 			}
 			if from.Equal(api.FeeAccumulatorAccountID) || to.Equal(api.FeeAccumulatorAccountID) {
-				gotFeeAcc = true
+				require.False(tokens.IsZero(), "FeeAccumulator xfer: amount should be non-zero")
 				continue
 			}
 
@@ -307,15 +302,13 @@ TransferWaitLoop:
 				gotTransfer = true
 			}
 
-			if (gotCommon || gotFeeAcc) && gotTransfer {
+			if gotTransfer {
 				break TransferWaitLoop
 			}
 		case <-time.After(recvTimeout):
 			t.Fatalf("failed to receive transfer event")
 		}
 	}
-
-	require.True(gotCommon || gotFeeAcc, "WatchEvents should also return transfer events related to the common pool and/or the fee accumulator")
 }
 
 func testSelfTransfer(t *testing.T, state *stakingTestsState, backend api.Backend, consensus consensusAPI.Backend) {
@@ -336,20 +329,18 @@ func testSelfTransfer(t *testing.T, state *stakingTestsState, backend api.Backen
 	err = consensusAPI.SignAndSubmitTx(context.Background(), consensus, srcSigner, tx)
 	require.NoError(err, "Transfer")
 
-	var gotCommon bool
-	var gotFeeAcc bool
 	var gotTransfer bool
 
 TransferWaitLoop:
 	for {
 		select {
 		case ev := <-ch:
 			if ev.From.Equal(api.CommonPoolAccountID) || ev.To.Equal(api.CommonPoolAccountID) {
-				gotCommon = true
+				require.False(ev.Tokens.IsZero(), "CommonPool xfer: amount should be non-zero")
 				continue
 			}
 			if ev.From.Equal(api.FeeAccumulatorAccountID) || ev.To.Equal(api.FeeAccumulatorAccountID) {
-				gotFeeAcc = true
+				require.False(ev.Tokens.IsZero(), "FeeAccumulator xfer: amount should be non-zero")
 				continue
 			}
 
@@ -360,16 +351,14 @@ TransferWaitLoop:
 				gotTransfer = true
 			}
 
-			if (gotCommon || gotFeeAcc) && gotTransfer {
+			if gotTransfer {
 				break TransferWaitLoop
 			}
 		case <-time.After(recvTimeout):
 			t.Fatalf("failed to receive transfer event")
 		}
 	}
 
-	require.True(gotCommon || gotFeeAcc, "WatchTransfers should also return transfers related to the common pool and/or the fee accumulator")
-
 	newSrcAcc, err := backend.AccountInfo(context.Background(), &api.OwnerQuery{Owner: SrcID, Height: consensusAPI.HeightLatest})
 	require.NoError(err, "src: AccountInfo - after")
 	require.Equal(srcAcc.General.Balance, newSrcAcc.General.Balance, "src: general balance - after")