Use type rather than field presence

[pinch] / pinch.py

diff --git a/pinch.py b/pinch.py
index 26982260cc62c5f485175c6ee77e84868909a0a5..bfc6ac635dfd0866e8cae54d56ac4a9c1daae44f 100644 (file)
--- a/pinch.py
+++ b/pinch.py
@@ -1,3 +1,4 @@
+from abc import ABC, abstractmethod
 import argparse
 import configparser
 import filecmp
@@ -85,12 +86,22 @@ class ChannelTableEntry(types.SimpleNamespace):
     url: str
 
 
-class SearchPath(types.SimpleNamespace):
+class SearchPath(types.SimpleNamespace, ABC):
     release_name: str
 
+    @abstractmethod
+    def pin(self, v: Verification, conf: configparser.SectionProxy) -> None:
+        pass
 
-class Channel(SearchPath):
+
+class AliasSearchPath(SearchPath):
     alias_of: str
+
+    def pin(self, v: Verification, conf: configparser.SectionProxy) -> None:
+        assert not hasattr(self, 'git_repo')
+
+
+class Channel(SearchPath):
     channel_html: bytes
     channel_url: str
     forwarded_url: str
@@ -101,10 +112,6 @@ class Channel(SearchPath):
     table: Dict[str, ChannelTableEntry]
 
     def pin(self, v: Verification, conf: configparser.SectionProxy) -> None:
-        if hasattr(self, 'alias_of'):
-            assert not hasattr(self, 'git_repo')
-            return
-
         if hasattr(self, 'git_revision'):
             self.old_git_revision = self.git_revision
             del self.git_revision
@@ -528,6 +535,8 @@ def git_revision_name(v: Verification, channel: Channel) -> str:
 
 
 def read_search_path(conf: configparser.SectionProxy) -> SearchPath:
+    if 'alias_of' in conf:
+        return AliasSearchPath(**dict(conf.items()))
     return Channel(**dict(conf.items()))
 
 
@@ -569,10 +578,10 @@ def update(args: argparse.Namespace) -> None:
     exprs: Dict[str, str] = {}
     config = read_config_files(args.channels_file)
     for section in config:
-        if 'alias_of' in config[section]:
+        sp = read_search_path(config[section])
+        if isinstance(sp, AliasSearchPath):
             assert 'git_repo' not in config[section]
             continue
-        sp = read_search_path(config[section])
         tarball = sp.fetch(v, section, config[section])
         exprs[section] = (
             'f: f { name = "%s"; channelName = "%%s"; src = builtins.storePath "%s"; }' %