Prefer more type-safe NamedTuple over SimpleNamespace

[pinch] / pinch.py

diff --git a/pinch.py b/pinch.py
index b76131399f6ee9d78188305a739e25c0aebf1b52..8fe7df16c10958ccaa6c0edfd8c7a834d444faa4 100644 (file)
--- a/pinch.py
+++ b/pinch.py
@@ -1,3 +1,4 @@
+from abc import ABC, abstractmethod

 import argparse
 import configparser
 import filecmp
 import argparse
 import configparser
 import filecmp


@@ -21,14 +22,19 @@ from typing import (
     Dict,
     Iterable,
     List,
     Dict,
     Iterable,
     List,

+    Mapping,
+    NamedTuple,

     NewType,
     NewType,

+    Optional,

     Tuple,
     Tuple,

+    Type,
+    Union,

 )
 
 # Use xdg module when it's less painful to have as a dependency
 
 
 )
 
 # Use xdg module when it's less painful to have as a dependency
 
 

-class XDG(types.SimpleNamespace):
+class XDG(NamedTuple):

     XDG_CACHE_HOME: str
 
 
     XDG_CACHE_HOME: str
 
 


@@ -38,31 +44,6 @@ xdg = XDG(
         os.path.expanduser('~/.cache')))
 
 
         os.path.expanduser('~/.cache')))
 
 

-Digest16 = NewType('Digest16', str)
-Digest32 = NewType('Digest32', str)
-
-
-class ChannelTableEntry(types.SimpleNamespace):
-    absolute_url: str
-    digest: Digest16
-    file: str
-    size: int
-    url: str
-
-
-class Channel(types.SimpleNamespace):
-    alias_of: str
-    channel_html: bytes
-    channel_url: str
-    forwarded_url: str
-    git_ref: str
-    git_repo: str
-    git_revision: str
-    old_git_revision: str
-    release_name: str
-    table: Dict[str, ChannelTableEntry]
-
-

 class VerificationError(Exception):
     pass
 
 class VerificationError(Exception):
     pass
 


@@ -98,6 +79,120 @@ class Verification:
         self.result(True)
 
 
         self.result(True)
 
 

+Digest16 = NewType('Digest16', str)
+Digest32 = NewType('Digest32', str)
+
+
+class ChannelTableEntry(types.SimpleNamespace):
+    absolute_url: str
+    digest: Digest16
+    file: str
+    size: int
+    url: str
+
+
+class AliasPin(NamedTuple):
+    pass
+
+
+class GitPin(NamedTuple):
+    git_revision: str
+    release_name: str
+
+
+class ChannelPin(NamedTuple):
+    git_revision: str
+    release_name: str
+    tarball_url: str
+    tarball_sha256: str
+
+
+Pin = Union[AliasPin, GitPin, ChannelPin]
+
+
+class SearchPath(types.SimpleNamespace, ABC):
+
+    @abstractmethod
+    def pin(self, v: Verification) -> Pin:
+        pass
+
+
+class AliasSearchPath(SearchPath):
+    alias_of: str
+
+    def pin(self, v: Verification) -> AliasPin:
+        assert not hasattr(self, 'git_repo')
+        return AliasPin()
+
+
+# (This lint-disable is for pylint bug https://github.com/PyCQA/pylint/issues/179
+# which is fixed in pylint 2.5.)
+class TarrableSearchPath(SearchPath, ABC):  # pylint: disable=abstract-method
+    channel_html: bytes
+    channel_url: str
+    forwarded_url: str
+    git_ref: str
+    git_repo: str
+    table: Dict[str, ChannelTableEntry]
+
+
+class GitSearchPath(TarrableSearchPath):
+    def pin(self, v: Verification) -> GitPin:
+        old_revision = (
+            self.git_revision if hasattr(self, 'git_revision') else None)
+        if hasattr(self, 'git_revision'):
+            del self.git_revision
+
+        new_revision = git_fetch(v, self, None, old_revision)
+        return GitPin(release_name=git_revision_name(v, self, new_revision),
+                      git_revision=new_revision)
+
+    def fetch(self, v: Verification, section: str,
+              conf: configparser.SectionProxy) -> str:
+        if 'git_revision' not in conf or 'release_name' not in conf:
+            raise Exception(
+                'Cannot update unpinned channel "%s" (Run "pin" before "update")' %
+                section)
+        the_pin = GitPin(
+            release_name=conf['release_name'],
+            git_revision=conf['git_revision'])
+
+        ensure_git_rev_available(v, self, the_pin, None)
+        return git_get_tarball(v, self, the_pin)
+
+
+class ChannelSearchPath(TarrableSearchPath):
+    def pin(self, v: Verification) -> ChannelPin:
+        old_revision = (
+            self.git_revision if hasattr(self, 'git_revision') else None)
+        if hasattr(self, 'git_revision'):
+            del self.git_revision
+
+        fetch(v, self)
+        new_gitpin = parse_channel(v, self)
+        fetch_resources(v, self, new_gitpin)
+        ensure_git_rev_available(v, self, new_gitpin, old_revision)
+        check_channel_contents(v, self, new_gitpin)
+        return ChannelPin(
+            release_name=new_gitpin.release_name,
+            tarball_url=self.table['nixexprs.tar.xz'].absolute_url,
+            tarball_sha256=self.table['nixexprs.tar.xz'].digest,
+            git_revision=new_gitpin.git_revision)
+
+    # Lint TODO: Put tarball_url and tarball_sha256 in ChannelSearchPath
+    # pylint: disable=no-self-use
+    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)
+
+        return fetch_with_nix_prefetch_url(
+            v, conf['tarball_url'], Digest16(
+                conf['tarball_sha256']))
+
+

 def compare(a: str, b: str) -> Tuple[List[str], List[str], List[str]]:
 
     def throw(error: OSError) -> None:
 def compare(a: str, b: str) -> Tuple[List[str], List[str], List[str]]:
 
     def throw(error: OSError) -> None:


@@ -126,16 +221,16 @@ def compare(a: str, b: str) -> Tuple[List[str], List[str], List[str]]:
     return filecmp.cmpfiles(a, b, files, shallow=False)
 
 
     return filecmp.cmpfiles(a, b, files, shallow=False)
 
 

-def fetch(v: Verification, channel: Channel) -> None:
+def fetch(v: Verification, channel: TarrableSearchPath) -> None:

     v.status('Fetching channel')
     request = urllib.request.urlopen(channel.channel_url, timeout=10)
     channel.channel_html = request.read()
     channel.forwarded_url = request.geturl()
     v.status('Fetching channel')
     request = urllib.request.urlopen(channel.channel_url, timeout=10)
     channel.channel_html = request.read()
     channel.forwarded_url = request.geturl()

-    v.result(request.status == 200)
+    v.result(request.status == 200)  # type: ignore  # (for old mypy)

     v.check('Got forwarded', channel.channel_url != channel.forwarded_url)
 
 
     v.check('Got forwarded', channel.channel_url != channel.forwarded_url)
 
 

-def parse_channel(v: Verification, channel: Channel) -> None:
+def parse_channel(v: Verification, channel: TarrableSearchPath) -> GitPin:

     v.status('Parsing channel description as XML')
     d = xml.dom.minidom.parseString(channel.channel_html)
     v.ok()
     v.status('Parsing channel description as XML')
     d = xml.dom.minidom.parseString(channel.channel_html)
     v.ok()


@@ -146,12 +241,11 @@ def parse_channel(v: Verification, channel: Channel) -> None:
     h1_name = d.getElementsByTagName('h1')[0].firstChild.nodeValue.split()[2]
     v.status(title_name)
     v.result(title_name == h1_name)
     h1_name = d.getElementsByTagName('h1')[0].firstChild.nodeValue.split()[2]
     v.status(title_name)
     v.result(title_name == h1_name)

-    channel.release_name = title_name

 
     v.status('Extracting git commit:')
     git_commit_node = d.getElementsByTagName('tt')[0]
 
     v.status('Extracting git commit:')
     git_commit_node = d.getElementsByTagName('tt')[0]

-    channel.git_revision = git_commit_node.firstChild.nodeValue
-    v.status(channel.git_revision)
+    git_revision = git_commit_node.firstChild.nodeValue
+    v.status(git_revision)

     v.ok()
     v.status('Verifying git commit label')
     v.result(git_commit_node.previousSibling.nodeValue == 'Git commit ')
     v.ok()
     v.status('Verifying git commit label')
     v.result(git_commit_node.previousSibling.nodeValue == 'Git commit ')


@@ -166,6 +260,7 @@ def parse_channel(v: Verification, channel: Channel) -> None:
         channel.table[name] = ChannelTableEntry(
             url=url, digest=digest, size=size)
     v.ok()
         channel.table[name] = ChannelTableEntry(
             url=url, digest=digest, size=size)
     v.ok()

+    return GitPin(release_name=title_name, git_revision=git_revision)

 
 
 def digest_string(s: bytes) -> Digest16:
 
 
 def digest_string(s: bytes) -> Digest16:


@@ -212,10 +307,13 @@ def fetch_with_nix_prefetch_url(
     v.status("Verifying file digest")
     file_digest = digest_file(path)
     v.result(file_digest == digest)
     v.status("Verifying file digest")
     file_digest = digest_file(path)
     v.result(file_digest == digest)

-    return path
+    return path  # type: ignore  # (for old mypy)

 
 
 
 

-def fetch_resources(v: Verification, channel: Channel) -> None:
+def fetch_resources(
+        v: Verification,
+        channel: ChannelSearchPath,
+        pin: GitPin) -> None:

     for resource in ['git-revision', 'nixexprs.tar.xz']:
         fields = channel.table[resource]
         fields.absolute_url = urllib.parse.urljoin(
     for resource in ['git-revision', 'nixexprs.tar.xz']:
         fields = channel.table[resource]
         fields.absolute_url = urllib.parse.urljoin(


@@ -225,7 +323,7 @@ def fetch_resources(v: Verification, channel: Channel) -> None:
     v.status('Verifying git commit on main page matches git commit in table')
     v.result(
         open(
     v.status('Verifying git commit on main page matches git commit in table')
     v.result(
         open(

-            channel.table['git-revision'].file).read(999) == channel.git_revision)
+            channel.table['git-revision'].file).read(999) == pin.git_revision)

 
 
 def git_cachedir(git_repo: str) -> str:
 
 
 def git_cachedir(git_repo: str) -> str:


@@ -235,17 +333,21 @@ def git_cachedir(git_repo: str) -> str:
         digest_string(git_repo.encode()))
 
 
         digest_string(git_repo.encode()))
 
 

-def tarball_cache_file(channel: Channel) -> str:
+def tarball_cache_file(channel: TarrableSearchPath, pin: GitPin) -> str:

     return os.path.join(
         xdg.XDG_CACHE_HOME,
         'pinch/git-tarball',
         '%s-%s-%s' %
         (digest_string(channel.git_repo.encode()),
     return os.path.join(
         xdg.XDG_CACHE_HOME,
         'pinch/git-tarball',
         '%s-%s-%s' %
         (digest_string(channel.git_repo.encode()),

-         channel.git_revision,
-         channel.release_name))
+         pin.git_revision,
+         pin.release_name))

 
 
 
 

-def verify_git_ancestry(v: Verification, channel: Channel) -> None:
+def verify_git_ancestry(
+        v: Verification,
+        channel: TarrableSearchPath,
+        new_revision: str,
+        old_revision: Optional[str]) -> None:

     cachedir = git_cachedir(channel.git_repo)
     v.status('Verifying rev is an ancestor of ref')
     process = subprocess.run(['git',
     cachedir = git_cachedir(channel.git_repo)
     v.status('Verifying rev is an ancestor of ref')
     process = subprocess.run(['git',


@@ -253,25 +355,29 @@ def verify_git_ancestry(v: Verification, channel: Channel) -> None:
                               cachedir,
                               'merge-base',
                               '--is-ancestor',
                               cachedir,
                               'merge-base',
                               '--is-ancestor',

-                              channel.git_revision,
+                              new_revision,

                               channel.git_ref])
     v.result(process.returncode == 0)
 
                               channel.git_ref])
     v.result(process.returncode == 0)
 

-    if hasattr(channel, 'old_git_revision'):
+    if old_revision is not None:

         v.status(
             'Verifying rev is an ancestor of previous rev %s' %
         v.status(
             'Verifying rev is an ancestor of previous rev %s' %

-            channel.old_git_revision)
+            old_revision)

         process = subprocess.run(['git',
                                   '-C',
                                   cachedir,
                                   'merge-base',
                                   '--is-ancestor',
         process = subprocess.run(['git',
                                   '-C',
                                   cachedir,
                                   'merge-base',
                                   '--is-ancestor',

-                                  channel.old_git_revision,
-                                  channel.git_revision])
+                                  old_revision,
+                                  new_revision])

         v.result(process.returncode == 0)
 
 
         v.result(process.returncode == 0)
 
 

-def git_fetch(v: Verification, channel: Channel) -> None:
+def git_fetch(
+        v: Verification,
+        channel: TarrableSearchPath,
+        desired_revision: Optional[str],
+        old_revision: Optional[str]) -> str:

     # It would be nice if we could share the nix git cache, but as of the time
     # of writing it is transitioning from gitv2 (deprecated) to gitv3 (not ready
     # yet), and trying to straddle them both is too far into nix implementation
     # It would be nice if we could share the nix git cache, but as of the time
     # of writing it is transitioning from gitv2 (deprecated) to gitv3 (not ready
     # yet), and trying to straddle them both is too far into nix implementation


@@ -297,47 +403,53 @@ def git_fetch(v: Verification, channel: Channel) -> None:
                                          channel.git_ref)])
     v.result(process.returncode == 0)
 
                                          channel.git_ref)])
     v.result(process.returncode == 0)
 

-    if hasattr(channel, 'git_revision'):
+    if desired_revision is not None:

         v.status('Verifying that fetch retrieved this rev')
         process = subprocess.run(
         v.status('Verifying that fetch retrieved this rev')
         process = subprocess.run(

-            ['git', '-C', cachedir, 'cat-file', '-e', channel.git_revision])
+            ['git', '-C', cachedir, 'cat-file', '-e', desired_revision])

         v.result(process.returncode == 0)
         v.result(process.returncode == 0)

-    else:
-        channel.git_revision = open(
-            os.path.join(
-                cachedir,
-                'refs',
-                'heads',
-                channel.git_ref)).read(999).strip()

 
 

-    verify_git_ancestry(v, channel)
+    new_revision = open(
+        os.path.join(
+            cachedir,
+            'refs',
+            'heads',
+            channel.git_ref)).read(999).strip()
+
+    verify_git_ancestry(v, channel, new_revision, old_revision)
+
+    return new_revision

 
 
 
 

-def ensure_git_rev_available(v: Verification, channel: Channel) -> None:
+def ensure_git_rev_available(
+        v: Verification,
+        channel: TarrableSearchPath,
+        pin: GitPin,
+        old_revision: Optional[str]) -> None:

     cachedir = git_cachedir(channel.git_repo)
     if os.path.exists(cachedir):
         v.status('Checking if we already have this rev:')
         process = subprocess.run(
     cachedir = git_cachedir(channel.git_repo)
     if os.path.exists(cachedir):
         v.status('Checking if we already have this rev:')
         process = subprocess.run(

-            ['git', '-C', cachedir, 'cat-file', '-e', channel.git_revision])
+            ['git', '-C', cachedir, 'cat-file', '-e', pin.git_revision])

         if process.returncode == 0:
             v.status('yes')
         if process.returncode == 1:
             v.status('no')
         v.result(process.returncode == 0 or process.returncode == 1)
         if process.returncode == 0:
         if process.returncode == 0:
             v.status('yes')
         if process.returncode == 1:
             v.status('no')
         v.result(process.returncode == 0 or process.returncode == 1)
         if process.returncode == 0:

-            verify_git_ancestry(v, channel)
+            verify_git_ancestry(v, channel, pin.git_revision, old_revision)

             return
             return

-    git_fetch(v, channel)
+    git_fetch(v, channel, pin.git_revision, old_revision)

 
 
 def compare_tarball_and_git(
         v: Verification,
 
 
 def compare_tarball_and_git(
         v: Verification,

-        channel: Channel,
+        pin: GitPin,

         channel_contents: str,
         git_contents: str) -> None:
     v.status('Comparing channel tarball with git checkout')
     match, mismatch, errors = compare(os.path.join(
         channel_contents: str,
         git_contents: str) -> None:
     v.status('Comparing channel tarball with git checkout')
     match, mismatch, errors = compare(os.path.join(

-        channel_contents, channel.release_name), git_contents)
+        channel_contents, pin.release_name), git_contents)

     v.ok()
     v.check('%d files match' % len(match), len(match) > 0)
     v.check('%d files differ' % len(mismatch), len(mismatch) == 0)
     v.ok()
     v.check('%d files match' % len(match), len(match) > 0)
     v.check('%d files differ' % len(mismatch), len(mismatch) == 0)


@@ -363,7 +475,10 @@ def compare_tarball_and_git(
         len(benign_errors) == len(expected_errors))
 
 
         len(benign_errors) == len(expected_errors))
 
 

-def extract_tarball(v: Verification, channel: Channel, dest: str) -> None:
+def extract_tarball(
+        v: Verification,
+        channel: TarrableSearchPath,
+        dest: str) -> None:

     v.status('Extracting tarball %s' %
              channel.table['nixexprs.tar.xz'].file)
     shutil.unpack_archive(
     v.status('Extracting tarball %s' %
              channel.table['nixexprs.tar.xz'].file)
     shutil.unpack_archive(


@@ -372,13 +487,17 @@ def extract_tarball(v: Verification, channel: Channel, dest: str) -> None:
     v.ok()
 
 
     v.ok()
 
 

-def git_checkout(v: Verification, channel: Channel, dest: str) -> None:
+def git_checkout(
+        v: Verification,
+        channel: TarrableSearchPath,
+        pin: GitPin,
+        dest: str) -> None:

     v.status('Checking out corresponding git revision')
     git = subprocess.Popen(['git',
                             '-C',
                             git_cachedir(channel.git_repo),
                             'archive',
     v.status('Checking out corresponding git revision')
     git = subprocess.Popen(['git',
                             '-C',
                             git_cachedir(channel.git_repo),
                             'archive',

-                            channel.git_revision],
+                            pin.git_revision],

                            stdout=subprocess.PIPE)
     tar = subprocess.Popen(
         ['tar', 'x', '-C', dest, '-f', '-'], stdin=git.stdout)
                            stdout=subprocess.PIPE)
     tar = subprocess.Popen(
         ['tar', 'x', '-C', dest, '-f', '-'], stdin=git.stdout)


@@ -389,8 +508,11 @@ def git_checkout(v: Verification, channel: Channel, dest: str) -> None:
     v.result(git.returncode == 0 and tar.returncode == 0)
 
 
     v.result(git.returncode == 0 and tar.returncode == 0)
 
 

-def git_get_tarball(v: Verification, channel: Channel) -> str:
-    cache_file = tarball_cache_file(channel)
+def git_get_tarball(
+        v: Verification,
+        channel: TarrableSearchPath,
+        pin: GitPin) -> str:
+    cache_file = tarball_cache_file(channel, pin)

     if os.path.exists(cache_file):
         cached_tarball = open(cache_file).read(9999)
         if os.path.exists(cached_tarball):
     if os.path.exists(cache_file):
         cached_tarball = open(cache_file).read(9999)
         if os.path.exists(cached_tarball):


@@ -398,17 +520,17 @@ def git_get_tarball(v: Verification, channel: Channel) -> str:
 
     with tempfile.TemporaryDirectory() as output_dir:
         output_filename = os.path.join(
 
     with tempfile.TemporaryDirectory() as output_dir:
         output_filename = os.path.join(

-            output_dir, channel.release_name + '.tar.xz')
+            output_dir, pin.release_name + '.tar.xz')

         with open(output_filename, 'w') as output_file:
             v.status(
                 'Generating tarball for git revision %s' %
         with open(output_filename, 'w') as output_file:
             v.status(
                 'Generating tarball for git revision %s' %

-                channel.git_revision)
+                pin.git_revision)

             git = subprocess.Popen(['git',
                                     '-C',
                                     git_cachedir(channel.git_repo),
                                     'archive',
             git = subprocess.Popen(['git',
                                     '-C',
                                     git_cachedir(channel.git_repo),
                                     'archive',

-                                    '--prefix=%s/' % channel.release_name,
-                                    channel.git_revision],
+                                    '--prefix=%s/' % pin.release_name,
+                                    pin.git_revision],

                                    stdout=subprocess.PIPE)
             xz = subprocess.Popen(['xz'], stdin=git.stdout, stdout=output_file)
             xz.wait()
                                    stdout=subprocess.PIPE)
             xz = subprocess.Popen(['xz'], stdin=git.stdout, stdout=output_file)
             xz.wait()


@@ -423,57 +545,55 @@ def git_get_tarball(v: Verification, channel: Channel) -> str:
 
         os.makedirs(os.path.dirname(cache_file), exist_ok=True)
         open(cache_file, 'w').write(store_tarball)
 
         os.makedirs(os.path.dirname(cache_file), exist_ok=True)
         open(cache_file, 'w').write(store_tarball)

-        return store_tarball
+        return store_tarball  # type: ignore  # (for old mypy)

 
 
 def check_channel_metadata(
         v: Verification,
 
 
 def check_channel_metadata(
         v: Verification,

-        channel: Channel,
+        pin: GitPin,

         channel_contents: str) -> None:
     v.status('Verifying git commit in channel tarball')
     v.result(
         open(
             os.path.join(
                 channel_contents,
         channel_contents: str) -> None:
     v.status('Verifying git commit in channel tarball')
     v.result(
         open(
             os.path.join(
                 channel_contents,

-                channel.release_name,
-                '.git-revision')).read(999) == channel.git_revision)
+                pin.release_name,
+                '.git-revision')).read(999) == pin.git_revision)

 
     v.status(
         'Verifying version-suffix is a suffix of release name %s:' %
 
     v.status(
         'Verifying version-suffix is a suffix of release name %s:' %

-        channel.release_name)
+        pin.release_name)

     version_suffix = open(
         os.path.join(
             channel_contents,
     version_suffix = open(
         os.path.join(
             channel_contents,

-            channel.release_name,
+            pin.release_name,

             '.version-suffix')).read(999)
     v.status(version_suffix)
             '.version-suffix')).read(999)
     v.status(version_suffix)

-    v.result(channel.release_name.endswith(version_suffix))
+    v.result(pin.release_name.endswith(version_suffix))

 
 
 
 

-def check_channel_contents(v: Verification, channel: Channel) -> None:
+def check_channel_contents(
+        v: Verification,
+        channel: TarrableSearchPath,
+        pin: GitPin) -> None:

     with tempfile.TemporaryDirectory() as channel_contents, \
             tempfile.TemporaryDirectory() as git_contents:
 
         extract_tarball(v, channel, channel_contents)
     with tempfile.TemporaryDirectory() as channel_contents, \
             tempfile.TemporaryDirectory() as git_contents:
 
         extract_tarball(v, channel, channel_contents)

-        check_channel_metadata(v, channel, channel_contents)
+        check_channel_metadata(v, pin, channel_contents)

 
 

-        git_checkout(v, channel, git_contents)
+        git_checkout(v, channel, pin, git_contents)

 
 

-        compare_tarball_and_git(v, channel, channel_contents, git_contents)
+        compare_tarball_and_git(v, pin, channel_contents, git_contents)

 
         v.status('Removing temporary directories')
     v.ok()
 
 
 
         v.status('Removing temporary directories')
     v.ok()
 
 

-def pin_channel(v: Verification, channel: Channel) -> None:
-    fetch(v, channel)
-    parse_channel(v, channel)
-    fetch_resources(v, channel)
-    ensure_git_rev_available(v, channel)
-    check_channel_contents(v, channel)
-
-
-def git_revision_name(v: Verification, channel: Channel) -> str:
+def git_revision_name(
+        v: Verification,
+        channel: TarrableSearchPath,
+        git_revision: str) -> str:

     v.status('Getting commit date')
     process = subprocess.run(['git',
                               '-C',
     v.status('Getting commit date')
     process = subprocess.run(['git',
                               '-C',


@@ -482,92 +602,73 @@ def git_revision_name(v: Verification, channel: Channel) -> str:
                               '-n1',
                               '--format=%ct-%h',
                               '--abbrev=11',
                               '-n1',
                               '--format=%ct-%h',
                               '--abbrev=11',

-                              channel.git_revision],
+                              '--no-show-signature',
+                              git_revision],

                              stdout=subprocess.PIPE)
     v.result(process.returncode == 0 and process.stdout != b'')
     return '%s-%s' % (os.path.basename(channel.git_repo),
                       process.stdout.decode().strip())
 
 
                              stdout=subprocess.PIPE)
     v.result(process.returncode == 0 and process.stdout != b'')
     return '%s-%s' % (os.path.basename(channel.git_repo),
                       process.stdout.decode().strip())
 
 

+def read_search_path(conf: configparser.SectionProxy) -> SearchPath:
+    mapping: Mapping[str, Type[SearchPath]] = {
+        'alias': AliasSearchPath,
+        'channel': ChannelSearchPath,
+        'git': GitSearchPath,
+    }
+    return mapping[conf['type']](**dict(conf.items()))
+
+

 def read_config(filename: str) -> configparser.ConfigParser:
     config = configparser.ConfigParser()
     config.read_file(open(filename), filename)
     return config
 
 
 def read_config(filename: str) -> configparser.ConfigParser:
     config = configparser.ConfigParser()
     config.read_file(open(filename), filename)
     return config
 
 

-def pin(args: argparse.Namespace) -> None:
+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 pinCommand(args: argparse.Namespace) -> None:

     v = Verification()
     config = read_config(args.channels_file)
     for section in config.sections():
         if args.channels and section not in args.channels:
             continue
 
     v = Verification()
     config = read_config(args.channels_file)
     for section in config.sections():
         if args.channels and section not in args.channels:
             continue
 

-        channel = Channel(**dict(config[section].items()))
-
-        if hasattr(channel, 'alias_of'):
-            assert not hasattr(channel, 'git_repo')
-            continue
-
-        if hasattr(channel, 'git_revision'):
-            channel.old_git_revision = channel.git_revision
-            del channel.git_revision
+        sp = read_search_path(config[section])

 
 

-        if 'channel_url' in config[section]:
-            pin_channel(v, channel)
-            config[section]['release_name'] = channel.release_name
-            config[section]['tarball_url'] = channel.table['nixexprs.tar.xz'].absolute_url
-            config[section]['tarball_sha256'] = channel.table['nixexprs.tar.xz'].digest
-        else:
-            git_fetch(v, channel)
-            config[section]['release_name'] = git_revision_name(v, channel)
-        config[section]['git_revision'] = channel.git_revision
+        config[section].update(sp.pin(v)._asdict())

 
     with open(args.channels_file, 'w') as configfile:
         config.write(configfile)
 
 
 
     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 = Channel(**dict(conf.items()))
-    ensure_git_rev_available(v, channel)
-    return git_get_tarball(v, channel)
-
-
-def update(args: argparse.Namespace) -> None:
+def updateCommand(args: argparse.Namespace) -> None:

     v = Verification()
     v = Verification()

-    config = configparser.ConfigParser()

     exprs: Dict[str, str] = {}
     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))
+    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 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'])]
+    for section in config:
+        if 'alias_of' in config[section]:
+            exprs[section] = exprs[str(config[section]['alias_of'])]

 
     command = [
         'nix-env',
 
     command = [
         'nix-env',


@@ -593,13 +694,14 @@ def main() -> None:
     parser_pin = subparsers.add_parser('pin')
     parser_pin.add_argument('channels_file', type=str)
     parser_pin.add_argument('channels', type=str, nargs='*')
     parser_pin = subparsers.add_parser('pin')
     parser_pin.add_argument('channels_file', type=str)
     parser_pin.add_argument('channels', type=str, nargs='*')

-    parser_pin.set_defaults(func=pin)
+    parser_pin.set_defaults(func=pinCommand)

     parser_update = subparsers.add_parser('update')
     parser_update.add_argument('--dry-run', action='store_true')
     parser_update.add_argument('channels_file', type=str, nargs='+')
     parser_update = subparsers.add_parser('update')
     parser_update.add_argument('--dry-run', action='store_true')
     parser_update.add_argument('channels_file', type=str, nargs='+')

-    parser_update.set_defaults(func=update)
+    parser_update.set_defaults(func=updateCommand)

     args = parser.parse_args()
     args.func(args)
 
 
     args = parser.parse_args()
     args.func(args)
 
 

-main()
+if __name__ == '__main__':
+    main()