Use type rather than field presence

[pinch] / pinch.py

diff --git a/pinch.py b/pinch.py
index d346a14f733a0ee071978b28b10e158cdfcaaf45..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
@@ -119,6 +126,21 @@ class Channel(SearchPath):
             conf['release_name'] = git_revision_name(v, self)
         conf['git_revision'] = self.git_revision
 
+    def fetch(self, v: Verification, section: str,
+              conf: configparser.SectionProxy) -> str:
+        if 'git_repo' not in conf or 'release_name' not in conf:
+            raise Exception(
+                'Cannot update unpinned channel "%s" (Run "pin" before "update")' %
+                section)
+
+        if 'channel_url' in conf:
+            return fetch_with_nix_prefetch_url(
+                v, conf['tarball_url'], Digest16(
+                    conf['tarball_sha256']))
+
+        ensure_git_rev_available(v, self)
+        return git_get_tarball(v, self)
+
 
 def compare(a: str, b: str) -> Tuple[List[str], List[str], List[str]]:
 
@@ -512,7 +534,9 @@ def git_revision_name(v: Verification, channel: Channel) -> str:
                       process.stdout.decode().strip())
 
 
-def read_search_path(conf: configparser.SectionProxy) -> Channel:
+def read_search_path(conf: configparser.SectionProxy) -> SearchPath:
+    if 'alias_of' in conf:
+        return AliasSearchPath(**dict(conf.items()))
     return Channel(**dict(conf.items()))
 
 
@@ -522,6 +546,18 @@ def read_config(filename: str) -> configparser.ConfigParser:
     return config
 
 
+def read_config_files(
+        filenames: Iterable[str]) -> Dict[str, configparser.SectionProxy]:
+    merged_config: Dict[str, configparser.SectionProxy] = {}
+    for file in filenames:
+        config = read_config(file)
+        for section in config.sections():
+            if section in merged_config:
+                raise Exception('Duplicate channel "%s"' % section)
+            merged_config[section] = config[section]
+    return merged_config
+
+
 def pin(args: argparse.Namespace) -> None:
     v = Verification()
     config = read_config(args.channels_file)
@@ -529,56 +565,31 @@ def pin(args: argparse.Namespace) -> None:
         if args.channels and section not in args.channels:
             continue
 
-        channel = read_search_path(config[section])
+        sp = read_search_path(config[section])
 
-        channel.pin(v, config[section])
+        sp.pin(v, config[section])
 
     with open(args.channels_file, 'w') as configfile:
         config.write(configfile)
 
 
-def fetch_channel(
-        v: Verification,
-        section: str,
-        conf: configparser.SectionProxy) -> str:
-    if 'git_repo' not in conf or 'release_name' not in conf:
-        raise Exception(
-            'Cannot update unpinned channel "%s" (Run "pin" before "update")' %
-            section)
-
-    if 'channel_url' in conf:
-        return fetch_with_nix_prefetch_url(
-            v, conf['tarball_url'], Digest16(
-                conf['tarball_sha256']))
-
-    channel = read_search_path(conf)
-    ensure_git_rev_available(v, channel)
-    return git_get_tarball(v, channel)
-
-
 def update(args: argparse.Namespace) -> None:
     v = Verification()
-    config = configparser.ConfigParser()
     exprs: Dict[str, str] = {}
-    configs = [read_config(filename) for filename in args.channels_file]
-    for config in configs:
-        for section in config.sections():
-            if 'alias_of' in config[section]:
-                assert 'git_repo' not in config[section]
-                continue
-            tarball = fetch_channel(v, section, config[section])
-            if section in exprs:
-                raise Exception('Duplicate channel "%s"' % section)
-            exprs[section] = (
-                'f: f { name = "%s"; channelName = "%%s"; src = builtins.storePath "%s"; }' %
-                (config[section]['release_name'], tarball))
-
-    for config in configs:
-        for section in config.sections():
-            if 'alias_of' in config[section]:
-                if section in exprs:
-                    raise Exception('Duplicate channel "%s"' % section)
-                exprs[section] = exprs[str(config[section]['alias_of'])]
+    config = read_config_files(args.channels_file)
+    for section in config:
+        sp = read_search_path(config[section])
+        if isinstance(sp, AliasSearchPath):
+            assert 'git_repo' not in config[section]
+            continue
+        tarball = sp.fetch(v, section, config[section])
+        exprs[section] = (
+            'f: f { name = "%s"; channelName = "%%s"; src = builtins.storePath "%s"; }' %
+            (config[section]['release_name'], tarball))
+
+    for section in config:
+        if 'alias_of' in config[section]:
+            exprs[section] = exprs[str(config[section]['alias_of'])]
 
     command = [
         'nix-env',