qml: add explanatory infomessage when sending capacity is significantly less than local balance.

Show message when attempting unfreeze of gossip channel in trampoline mode

electrum/gui/qml/components/ChannelDetails.qml

@@ -135,9 +135,10 @@ Pane {
                                 icon.source: '../../icons/share.png'
                                 icon.color: 'transparent'
                                 onClicked: {
-                                    var dialog = app.genericShareDialog.createObject(root,
-                                        { title: qsTr('Channel node ID'), text: channeldetails.pubkey }
-                                    )
+                                    var dialog = app.genericShareDialog.createObject(root, {
+                                        title: qsTr('Channel node ID'),
+                                        text: channeldetails.pubkey
+                                    })
                                     dialog.open()
                                 }
                             }
@@ -159,6 +160,18 @@ Pane {
                         columns: 2
                         rowSpacing: constants.paddingSmall
 
+                        InfoTextArea {
+                            Layout.columnSpan: 2
+                            Layout.fillWidth: true
+                            Layout.bottomMargin: constants.paddingMedium
+                            visible: channeldetails.canSend.msatsInt < 0.5 * channeldetails.localCapacity.msatsInt
+                                && channeldetails.localCapacity.msatsInt > 0.2 * channeldetails.capacity.msatsInt
+                            iconStyle: InfoTextArea.IconStyle.Warn
+                            compact: true
+                            text: [qsTr('The amount available for sending is considerably lower than the local balance.'),
+                                qsTr('This can occur when mempool fees are high.')].join(' ')
+                        }
+
                         ChannelBar {
                             Layout.columnSpan: 2
                             Layout.fillWidth: true
@@ -222,7 +235,7 @@ Pane {
                         }
 
                         Label {
-                            text: qsTr('Can Receive')
+                            text: qsTr('Can receive')
                             color: Material.accentColor
                         }
 
@@ -324,6 +337,14 @@ Pane {
         id: channeldetails
         wallet: Daemon.currentWallet
         channelid: root.channelid
+        onTrampolineFrozenInGossipMode: {
+            var dialog = app.messageDialog.createObject(root, {
+                title: qsTr('Cannot unfreeze channel'),
+                text: [qsTr('Non-Trampoline channels cannot be used for sending while in trampoline mode.'),
+                        qsTr('Disable trampoline mode to enable sending from this channel.')].join(' ')
+            })
+            dialog.open()
+        }
     }
 
     Component {

electrum/gui/qml/qechanneldetails.py

@@ -27,6 +27,7 @@ class QEChannelDetails(AuthMixin, QObject, QtEventListener):
     channelCloseSuccess = pyqtSignal()
     channelCloseFailed = pyqtSignal([str], arguments=['message'])
     isClosingChanged = pyqtSignal()
+    trampolineFrozenInGossipMode = pyqtSignal()
 
     def __init__(self, parent=None):
         super().__init__(parent)
@@ -214,6 +215,7 @@ class QEChannelDetails(AuthMixin, QObject, QtEventListener):
             self.channelChanged.emit()
         else:
             self._logger.debug(messages.MSG_NON_TRAMPOLINE_CHANNEL_FROZEN_WITHOUT_GOSSIP)
+            self.trampolineFrozenInGossipMode.emit()
 
     @pyqtSlot()
     def freezeForReceiving(self):