invoices: don't modify .amount_msat directly

electrum/gui/kivy/uix/screens.py

@@ -351,7 +351,7 @@ class SendScreen(CScreen, Logger):
                 assert type(amount_sat) is int
                 invoice = Invoice.from_bech32(address)
                 if invoice.amount_msat is None:
-                    invoice.amount_msat = int(amount_sat * 1000)
+                    invoice.set_amount_msat(int(amount_sat * 1000))
                 return invoice
             else:
                 # on-chain

electrum/gui/qml/qeinvoice.py

@@ -379,8 +379,7 @@ class QEInvoice(QObject, QtEventListener):
         if self.amount.isEmpty:
             if self.amountOverride.isEmpty:
                 raise Exception('can not pay 0 amount')
-            # TODO: is update amount_msat for overrideAmount sufficient?
-            self._effectiveInvoice.amount_msat = self.amountOverride.satsInt * 1000
+            self._effectiveInvoice.set_amount_msat(self.amountOverride.satsInt * 1000)
 
         self._wallet.pay_lightning_invoice(self._effectiveInvoice)
 
@@ -627,9 +626,9 @@ class QEInvoiceParser(QEInvoice):
 
         if not self._effectiveInvoice.amount_msat and not self.amountOverride.isEmpty:
             if self.invoiceType == QEInvoice.Type.OnchainInvoice and self.amountOverride.isMax:
-                self._effectiveInvoice.amount_msat = '!'
+                self._effectiveInvoice.set_amount_msat('!')
             else:
-                self._effectiveInvoice.amount_msat = self.amountOverride.satsInt * 1000
+                self._effectiveInvoice.set_amount_msat(self.amountOverride.satsInt * 1000)
 
         self.canSave = False
 

electrum/gui/text.py

@@ -606,7 +606,7 @@ class ElectrumGui(BaseElectrumGui, EventListener):
             if invoice.amount_msat is None:
                 amount_sat = self.parse_amount(self.str_amount)
                 if amount_sat:
-                    invoice.amount_msat = int(amount_sat * 1000)
+                    invoice.set_amount_msat(int(amount_sat * 1000))
                 else:
                     self.show_error(_('No amount'))
                     return

electrum/invoices.py

@@ -178,6 +178,19 @@ class BaseInvoice(StoredObject):
             return amount_msat
         return int(amount_msat // 1000)
 
+    def set_amount_msat(self, amount_msat: Union[int, str]) -> None:
+        """The GUI uses this to fill the amount for a zero-amount invoice."""
+        if amount_msat == "!":
+            amount_sat = amount_msat
+        else:
+            assert isinstance(amount_msat, int), f"{amount_msat=!r}"
+            assert amount_msat >= 0, amount_msat
+            amount_sat = (amount_msat // 1000) + int(amount_msat % 1000 > 0)  # round up
+        if outputs := self.outputs:
+            assert len(self.outputs) == 1, len(self.outputs)
+            self.outputs = [PartialTxOutput(scriptpubkey=outputs[0].scriptpubkey, value=amount_sat)]
+        self.amount_msat = amount_msat
+
     @amount_msat.validator
     def _validate_amount(self, attribute, value):
         if value is None:

electrum/payment_identifier.py

@@ -674,7 +674,7 @@ def invoice_from_payment_identifier(
         if not invoice:
             return
         if invoice.amount_msat is None:
-            invoice.amount_msat = int(amount_sat * 1000)
+            invoice.set_amount_msat(int(amount_sat * 1000))
         return invoice
     else:
         outputs = pi.get_onchain_outputs(amount_sat)

electrum/tests/test_invoices.py

@@ -286,6 +286,8 @@ class TestBaseInvoice(ElectrumTestCase):
         )
         with self.assertRaises(InvoiceError):
             invoice.amount_msat = 10**20
+        with self.assertRaises(InvoiceError):
+            invoice.set_amount_msat(10**20)
         with self.assertRaises(InvoiceError):
             invoice2 = Invoice(
                 amount_msat=10**20,