keystore: encapsulate "can_have_deterministic_lightning_xprv" logic

electrum/base_wizard.py

@@ -545,7 +545,7 @@ class BaseWizard(Logger):
 
     def create_keystore(self, seed, passphrase):
         k = keystore.from_seed(seed, passphrase, self.wallet_type == 'multisig')
-        if self.wallet_type == 'standard' and self.seed_type == 'segwit':
+        if k.can_have_deterministic_lightning_xprv():
             self.data['lightning_xprv'] = k.get_lightning_xprv(None)
         self.on_keystore(k)
 

electrum/keystore.py

@@ -160,6 +160,9 @@ class KeyStore(Logger, ABC):
                 return pubkey, list(path)
         return None, None
 
+    def can_have_deterministic_lightning_xprv(self) -> bool:
+        return False
+
 
 class Software_KeyStore(KeyStore):
 
@@ -620,7 +623,14 @@ class BIP32_KeyStore(Xpub, Deterministic_KeyStore):
         cK = ecc.ECPrivkey(k).get_public_key_bytes()
         return cK, k
 
-    def get_lightning_xprv(self, password):
+    def can_have_deterministic_lightning_xprv(self):
+        if (self.get_seed_type() == 'segwit'
+                and self.get_bip32_node_for_xpub().xtype == 'p2wpkh'):
+            return True
+        return False
+
+    def get_lightning_xprv(self, password) -> str:
+        assert self.can_have_deterministic_lightning_xprv()
         xprv = self.get_master_private_key(password)
         rootnode = BIP32Node.from_xkey(xprv)
         node = rootnode.subkey_at_private_derivation("m/67'/")

electrum/wallet.py

@@ -3185,7 +3185,7 @@ def create_new_wallet(*, path, config: SimpleConfig, passphrase=None, password=N
     k = keystore.from_seed(seed, passphrase)
     db.put('keystore', k.dump())
     db.put('wallet_type', 'standard')
-    if keystore.seed_type(seed) == 'segwit':
+    if k.can_have_deterministic_lightning_xprv():
         db.put('lightning_xprv', k.get_lightning_xprv(None))
     if gap_limit is not None:
         db.put('gap_limit', gap_limit)
@@ -3229,7 +3229,7 @@ def restore_wallet_from_text(text, *, path, config: SimpleConfig,
             k = keystore.from_master_key(text)
         elif keystore.is_seed(text):
             k = keystore.from_seed(text, passphrase)
-            if keystore.seed_type(text) == 'segwit':
+            if k.can_have_deterministic_lightning_xprv():
                 db.put('lightning_xprv', k.get_lightning_xprv(None))
         else:
             raise Exception("Seed or key not recognized")