imp(erc20: Emit additional approval event in case of transferFrom

CHANGELOG.md

@@ -118,6 +118,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 - (erc20) [#2080](https://github.com/evmos/evmos/pull/2080) Add ERC20 integration test setup.
 - (erc20) [#2085](https://github.com/evmos/evmos/pull/2085) Add ERC20 transfer integration tests.
 - (erc20) [#2086](https://github.com/evmos/evmos/pull/2086) Add ERC20 metadata query integration tests.
+- (erc20) [#2088](https://github.com/evmos/evmos/pull/2088) Emit additional approval event in case of `transferFrom`.
 
 ### Bug Fixes
 

precompiles/erc20/integration_test.go

@@ -393,6 +393,11 @@ var _ = Describe("ERC20 Extension -", func() {
 					_, _, err := is.factory.CallContractAndCheckLogs(owner.Priv, txArgs, approveArgs, approveCheck)
 					Expect(err).ToNot(HaveOccurred(), "unexpected result calling contract")
 
+					is.ExpectSendAuthzForContract(
+						callType, contractsData,
+						owner.Addr, owner.Addr, transferCoins,
+					)
+
 					// Transfer tokens
 					txArgs, transferArgs := is.getTxAndCallArgs(
 						callType, contractsData,
@@ -422,6 +427,8 @@ var _ = Describe("ERC20 Extension -", func() {
 					)
 
 					// Check that the allowance was removed since we authorized only the transferred amount
+					// FIXME: This is not working for the case where we transfer from the own account
+					// because the allowance is not removed on the SDK side.
 					is.ExpectNoSendAuthzForContract(
 						callType, contractsData,
 						owner.Addr, owner.Addr,

precompiles/erc20/tx.go

@@ -5,7 +5,9 @@ package erc20
 import (
 	"math/big"
 
+	errorsmod "cosmossdk.io/errors"
 	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/x/authz"
 	bankkeeper "github.com/cosmos/cosmos-sdk/x/bank/keeper"
 	banktypes "github.com/cosmos/cosmos-sdk/x/bank/types"
 	"github.com/ethereum/go-ethereum/accounts/abi"
@@ -75,17 +77,24 @@ func (p Precompile) transfer(
 
 	msg := banktypes.NewMsgSend(from.Bytes(), to.Bytes(), coins)
 
-	if err := msg.ValidateBasic(); err != nil {
+	if err = msg.ValidateBasic(); err != nil {
 		return nil, err
 	}
 
-	sender := sdk.AccAddress(from.Bytes())
-	spender := sdk.AccAddress(contract.CallerAddress.Bytes()) // aka. grantee
+	isTransferFrom := method.Name == TransferFromMethod
+	spenderAddr := contract.CallerAddress
+	spender := sdk.AccAddress(spenderAddr.Bytes()) // aka. grantee
 
-	if sender.Equals(spender) {
+	var prevAllowance *big.Int
+	if !isTransferFrom {
 		msgSrv := bankkeeper.NewMsgServerImpl(p.bankKeeper)
 		_, err = msgSrv.Send(sdk.WrapSDKContext(ctx), msg)
 	} else {
+		_, _, prevAllowance, err = GetAuthzExpirationAndAllowance(p.AuthzKeeper, ctx, spenderAddr, from, p.tokenPair.Denom)
+		if err != nil {
+			return nil, ConvertErrToERC20Error(errorsmod.Wrapf(authz.ErrNoAuthorizationFound, err.Error()))
+		}
+
 		_, err = p.AuthzKeeper.DispatchActions(ctx, spender, []sdk.Msg{msg})
 	}
 
@@ -95,7 +104,18 @@ func (p Precompile) transfer(
 		return nil, err
 	}
 
-	if err := p.EmitTransferEvent(ctx, stateDB, from, to, amount); err != nil {
+	if err = p.EmitTransferEvent(ctx, stateDB, from, to, amount); err != nil {
+		return nil, err
+	}
+
+	// NOTE: if it's a direct transfer, we return here but if used through transferFrom,
+	// we need to emit the approval event with the new allowance.
+	if !isTransferFrom {
+		return method.Outputs.Pack(true)
+	}
+
+	newAllowance := new(big.Int).Sub(prevAllowance, amount)
+	if err = p.EmitApprovalEvent(ctx, stateDB, from, spenderAddr, newAllowance); err != nil {
 		return nil, err
 	}