feat: Add warning if sending tokens directly to contract

Fixes #936.

![imgur](https://imgur.com/XuzmdRs.png)

src/app/wallet/view.nim

@@ -518,6 +518,9 @@ QtObject:
     if self.fetchingHistoryState.hasKey(address):
       return self.fetchingHistoryState[address]
     return true
+  
+  proc isKnownTokenContract*(self: WalletView, address: string): bool {.slot.} =
+    return self.status.wallet.getKnownTokenContract(parseAddress(address)) != nil
 
   proc isHistoryFetched*(self: WalletView, address: string): bool {.slot.} =
     return self.currentTransactions.rowCount() > 0

src/status/wallet.nim

@@ -67,6 +67,9 @@ proc buildTokenTransaction(self: WalletModel, source, to, assetAddress: Address,
   transfer = Transfer(to: to, value: eth2Wei(value, contract.decimals))
   transactions.buildTokenTransaction(source, assetAddress, gas, gasPrice)
 
+proc getKnownTokenContract*(self: WalletModel, address: Address): Erc20Contract =
+  getErc20Contracts().concat(getCustomTokens()).getErc20ContractByAddress(address)
+
 proc estimateGas*(self: WalletModel, source, to, value: string, success: var bool): int =
   var tx = transactions.buildTransaction(
     parseAddress(source),

ui/app/AppLayouts/Wallet/SendModal.qml

@@ -193,6 +193,14 @@ ModalPopup {
                     })
                 }
             }
+            SendToContractWarning {
+                id: sendToContractWarning
+                anchors.top: pvwTransaction.bottom
+                selectedRecipient: selectRecipient.selectedRecipient
+                reset: function() {
+                    selectedRecipient = Qt.binding(function() { return selectRecipient.selectedRecipient })
+                }
+            }
         }
         TransactionFormGroup {
             id: group4

ui/nim-status-client.pro

@@ -359,6 +359,7 @@ DISTFILES += \
     shared/RoundedImage.qml \
     shared/SearchBox.qml \
     shared/Select.qml \
+    shared/SendToContractWarning.qml \
     shared/Separator.qml \
     shared/SeparatorWithIcon.qml \
     shared/SplitViewHandle.qml \

ui/shared/SendToContractWarning.qml

@@ -0,0 +1,67 @@
+import QtQuick 2.13
+import QtQuick.Controls 2.13
+import QtQuick.Layouts 1.13
+import "../imports"
+import "./"
+
+Item {
+    id: root
+    anchors.left: parent.left
+    anchors.right: parent.right
+    property string sendToContractWarningMessage: qsTr("Tokens will be sent directly to a contract address, which may result in a loss of funds. To transfer ERC-20 tokens, ensure the recipient address is the address of the destination wallet.")
+    property var selectedRecipient
+    property bool isValid: true
+    property var reset: function() {}
+
+    onSelectedRecipientChanged: validate()
+
+    function resetInternal() {
+        selectedRecipient = undefined
+        isValid = true
+    }
+
+    function validate() {
+        let isValid = true
+        if (!(selectedRecipient && selectedRecipient.address)) {
+            return root.isValid
+        }
+        txtValidationError.text = ""
+        if (walletModel.isKnownTokenContract(selectedRecipient.address)) {
+            // do not set isValid = false here because it would make the
+            // TransactionStackGroup invalid and therefore not let the user
+            // continue in the modal
+            txtValidationError.text = sendToContractWarningMessage
+        }
+        return isValid
+    }
+
+    Column {
+        id: colValidation
+        anchors.horizontalCenter: parent.horizontalCenter
+        visible: txtValidationError.text !== ""
+        spacing: 5
+
+        SVGImage {
+            id: imgExclamation
+            width: 13.33
+            height: 13.33
+            sourceSize.height: height * 2
+            sourceSize.width: width * 2
+            anchors.horizontalCenter: parent.horizontalCenter
+            fillMode: Image.PreserveAspectFit
+            source: "../app/img/exclamation_outline.svg"
+        }
+        StyledText {
+            id: txtValidationError
+            text: ""
+            width: root.width
+            verticalAlignment: Text.AlignVCenter
+            horizontalAlignment: Text.AlignHCenter
+            font.pixelSize: 13
+            color: Style.current.danger
+            lineHeight: 18
+            lineHeightMode: Text.FixedHeight
+            wrapMode: Text.WordWrap
+        }
+    }
+}