README: Link auto-upgrade-with-pinch

[pinch] / pinch.py

diff --git a/pinch.py b/pinch.py
index b76c8da36db18e4b608fad64c5e4bbd422b8c948..9e80c01436aa2071501be22e3048f70473ef4aad 100644 (file)
--- a/pinch.py
+++ b/pinch.py
@@ -1,4 +1,10 @@
-from abc import ABC, abstractmethod
+# pinch: PIN CHannels - a replacement for `nix-channel --update`
+#
+# This program is free software: you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by the
+# Free Software Foundation, version 3.
+
+

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


@@ -12,6 +18,7 @@ import shlex
 import shutil
 import subprocess
 import sys
 import shutil
 import subprocess
 import sys

+import tarfile

 import tempfile
 import types
 import urllib.parse
 import tempfile
 import types
 import urllib.parse


@@ -19,17 +26,27 @@ import urllib.request
 import xml.dom.minidom
 
 from typing import (
 import xml.dom.minidom
 
 from typing import (

+    Callable,

     Dict,
     Iterable,
     List,
     Dict,
     Iterable,
     List,

+    Mapping,
+    NamedTuple,

     NewType,
     NewType,

+    Optional,
+    Set,

     Tuple,
     Tuple,

+    Type,
+    TypeVar,
+    Union,

 )
 
 )
 

+import git_cache
+

 # 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
 
 


@@ -54,7 +71,7 @@ class Verification:
 
     @staticmethod
     def _color(s: str, c: int) -> str:
 
     @staticmethod
     def _color(s: str, c: int) -> str:

-        return '\033[%2dm%s\033[00m' % (c, s)
+        return f'\033[{c:2d}m{s}\033[00m'

 
     def result(self, r: bool) -> None:
         message, color = {True: ('OK ', 92), False: ('FAIL', 91)}[r]
 
     def result(self, r: bool) -> None:
         message, color = {True: ('OK ', 92), False: ('FAIL', 91)}[r]


@@ -86,68 +103,122 @@ class ChannelTableEntry(types.SimpleNamespace):
     url: str
 
 
     url: str
 
 

-class SearchPath(types.SimpleNamespace, ABC):
+class AliasPin(NamedTuple):
+    pass
+
+
+class SymlinkPin(NamedTuple):
+    @property
+    def release_name(self) -> str:
+        return 'link'
+
+
+class GitPin(NamedTuple):
+    git_revision: str
+    release_name: str
+
+
+class ChannelPin(NamedTuple):
+    git_revision: str

     release_name: str
     release_name: str

+    tarball_url: str
+    tarball_sha256: str
+
+
+Pin = Union[AliasPin, SymlinkPin, GitPin, ChannelPin]
+
+
+def copy_to_nix_store(v: Verification, filename: str) -> str:
+    v.status('Putting tarball in Nix store')
+    process = subprocess.run(
+        ['nix-store', '--add', filename], stdout=subprocess.PIPE)
+    v.result(process.returncode == 0)
+    return process.stdout.decode().strip()  # type: ignore  # (for old mypy)
+

 
 

-    @abstractmethod
-    def pin(self, v: Verification, conf: configparser.SectionProxy) -> None:
-        pass
+def symlink_archive(v: Verification, path: str) -> str:
+    with tempfile.TemporaryDirectory() as td:
+        archive_filename = os.path.join(td, 'link.tar.gz')
+        os.symlink(path, os.path.join(td, 'link'))
+        with tarfile.open(archive_filename, mode='x:gz') as t:
+            t.add(os.path.join(td, 'link'), arcname='link')
+        return copy_to_nix_store(v, archive_filename)

 
 
 
 

-class AliasSearchPath(SearchPath):
+class AliasSearchPath(NamedTuple):

     alias_of: str
 
     alias_of: str
 

-    def pin(self, v: Verification, conf: configparser.SectionProxy) -> None:
-        assert not hasattr(self, 'git_repo')
+    def pin(self, _: Verification, __: Optional[Pin]) -> AliasPin:
+        return AliasPin()

 
 
 
 

-class TarrableSearchPath(SearchPath):
-    channel_html: bytes
-    channel_url: str
-    forwarded_url: str
-    git_ref: str
-    git_repo: str
-    git_revision: str
-    old_git_revision: str
-    table: Dict[str, ChannelTableEntry]
-
-    def pin(self, v: Verification, conf: configparser.SectionProxy) -> None:
-        if hasattr(self, 'git_revision'):
-            self.old_git_revision = self.git_revision
-            del self.git_revision
-
-        if 'channel_url' in conf:
-            pin_channel(v, self)
-            conf['release_name'] = self.release_name
-            conf['tarball_url'] = self.table['nixexprs.tar.xz'].absolute_url
-            conf['tarball_sha256'] = self.table['nixexprs.tar.xz'].digest
-        else:
-            git_fetch(v, self)
-            conf['release_name'] = git_revision_name(v, self)
-        conf['git_revision'] = self.git_revision
+class SymlinkSearchPath(NamedTuple):
+    path: str
+
+    def pin(self, _: Verification, __: Optional[Pin]) -> SymlinkPin:
+        return SymlinkPin()

 
 

-    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)
+    def fetch(self, v: Verification, _: Pin) -> str:
+        return symlink_archive(v, self.path)

 
 

-        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)
+class GitSearchPath(NamedTuple):
+    git_ref: str
+    git_repo: str

 
 

+    def pin(self, v: Verification, old_pin: Optional[Pin]) -> GitPin:
+        _, new_revision = git_cache.fetch(self.git_repo, self.git_ref)
+        if old_pin is not None:
+            assert isinstance(old_pin, GitPin)
+            verify_git_ancestry(v, self, old_pin.git_revision, new_revision)
+        return GitPin(release_name=git_revision_name(v, self, new_revision),
+                      git_revision=new_revision)

 
 

-class GitSearchPath(TarrableSearchPath):
-    pass
+    def fetch(self, v: Verification, pin: Pin) -> str:
+        assert isinstance(pin, GitPin)
+        git_cache.ensure_rev_available(
+            self.git_repo, self.git_ref, pin.git_revision)
+        return git_get_tarball(v, self, pin)

 
 
 
 

-class ChannelSearchPath(TarrableSearchPath):
-    pass
+class ChannelSearchPath(NamedTuple):
+    channel_url: str
+    git_ref: str
+    git_repo: str
+
+    def pin(self, v: Verification, old_pin: Optional[Pin]) -> ChannelPin:
+        if old_pin is not None:
+            assert isinstance(old_pin, ChannelPin)
+
+        channel_html, forwarded_url = fetch_channel(v, self)
+        table, new_gitpin = parse_channel(v, channel_html)
+        if old_pin is not None and old_pin.git_revision == new_gitpin.git_revision:
+            return old_pin
+        fetch_resources(v, new_gitpin, forwarded_url, table)
+        git_cache.ensure_rev_available(
+            self.git_repo, self.git_ref, new_gitpin.git_revision)
+        if old_pin is not None:
+            verify_git_ancestry(
+                v, self, old_pin.git_revision, new_gitpin.git_revision)
+        check_channel_contents(v, self, table, new_gitpin)
+        return ChannelPin(
+            release_name=new_gitpin.release_name,
+            tarball_url=table['nixexprs.tar.xz'].absolute_url,
+            tarball_sha256=table['nixexprs.tar.xz'].digest,
+            git_revision=new_gitpin.git_revision)
+
+    def fetch(self, v: Verification, pin: Pin) -> str:
+        assert isinstance(pin, ChannelPin)
+
+        return fetch_with_nix_prefetch_url(
+            v, pin.tarball_url, Digest16(pin.tarball_sha256))
+
+
+SearchPath = Union[AliasSearchPath,
+                   SymlinkSearchPath,
+                   GitSearchPath,
+                   ChannelSearchPath]
+TarrableSearchPath = Union[GitSearchPath, ChannelSearchPath]

 
 
 def compare(a: str, b: str) -> Tuple[List[str], List[str], List[str]]:
 
 
 def compare(a: str, b: str) -> Tuple[List[str], List[str], List[str]]:


@@ -178,46 +249,62 @@ 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: 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.result(request.status == 200)  # type: ignore  # (for old mypy)
-    v.check('Got forwarded', channel.channel_url != channel.forwarded_url)
+def fetch_channel(
+        v: Verification, channel: ChannelSearchPath) -> Tuple[str, str]:
+    v.status(f'Fetching channel from {channel.channel_url}')
+    with urllib.request.urlopen(channel.channel_url, timeout=10) as request:
+        channel_html = request.read().decode()
+        forwarded_url = request.geturl()
+        v.result(request.status == 200)
+    v.check('Got forwarded', channel.channel_url != forwarded_url)
+    return channel_html, forwarded_url

 
 
 
 

-def parse_channel(v: Verification, channel: TarrableSearchPath) -> None:
+def parse_channel(v: Verification, channel_html: str) \
+        -> Tuple[Dict[str, ChannelTableEntry], GitPin]:

     v.status('Parsing channel description as XML')
     v.status('Parsing channel description as XML')

-    d = xml.dom.minidom.parseString(channel.channel_html)
+    d = xml.dom.minidom.parseString(channel_html)

     v.ok()
 
     v.ok()
 

-    v.status('Extracting release name:')
-    title_name = d.getElementsByTagName(
-        'title')[0].firstChild.nodeValue.split()[2]
-    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:')
+    v.status('Finding release name (1)')
+    title = d.getElementsByTagName('title')[0].firstChild
+    v.result(isinstance(title, xml.dom.minidom.CharacterData))
+    assert isinstance(title, xml.dom.minidom.CharacterData)
+    release_name = title.nodeValue.split()[2]
+    v.status('Finding release name (2)')
+    h1 = d.getElementsByTagName('h1')[0].firstChild
+    v.result(isinstance(h1, xml.dom.minidom.CharacterData))
+    assert isinstance(h1, xml.dom.minidom.CharacterData)
+    v.status('Verifying release name:')
+    v.status(release_name)
+    v.result(release_name == h1.nodeValue.split()[2])
+
+    v.status('Finding git commit')

     git_commit_node = d.getElementsByTagName('tt')[0]
     git_commit_node = d.getElementsByTagName('tt')[0]

-    channel.git_revision = git_commit_node.firstChild.nodeValue
-    v.status(channel.git_revision)
+    v.result(
+        isinstance(
+            git_commit_node.firstChild,
+            xml.dom.minidom.CharacterData))
+    assert isinstance(
+        git_commit_node.firstChild,
+        xml.dom.minidom.CharacterData)
+    v.status('Extracting git commit:')
+    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.status('Parsing table')
     v.ok()
     v.status('Verifying git commit label')
     v.result(git_commit_node.previousSibling.nodeValue == 'Git commit ')
 
     v.status('Parsing table')

-    channel.table = {}
+    table: Dict[str, ChannelTableEntry] = {}

     for row in d.getElementsByTagName('tr')[1:]:
         name = row.childNodes[0].firstChild.firstChild.nodeValue
         url = row.childNodes[0].firstChild.getAttribute('href')
         size = int(row.childNodes[1].firstChild.nodeValue)
         digest = Digest16(row.childNodes[2].firstChild.firstChild.nodeValue)
     for row in d.getElementsByTagName('tr')[1:]:
         name = row.childNodes[0].firstChild.firstChild.nodeValue
         url = row.childNodes[0].firstChild.getAttribute('href')
         size = int(row.childNodes[1].firstChild.nodeValue)
         digest = Digest16(row.childNodes[2].firstChild.firstChild.nodeValue)

-        channel.table[name] = ChannelTableEntry(
-            url=url, digest=digest, size=size)
+        table[name] = ChannelTableEntry(url=url, digest=digest, size=size)

     v.ok()
     v.ok()

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

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


@@ -233,18 +320,39 @@ def digest_file(filename: str) -> Digest16:
     return Digest16(hasher.hexdigest())
 
 
     return Digest16(hasher.hexdigest())
 
 

+@functools.lru_cache
+def _experimental_flag_needed(v: Verification) -> bool:
+    v.status('Checking Nix version')
+    process = subprocess.run(['nix', '--help'], stdout=subprocess.PIPE)
+    v.result(process.returncode == 0)
+    return b'--experimental-features' in process.stdout
+
+
+def _nix_command(v: Verification) -> List[str]:
+    return ['nix', '--experimental-features',
+            'nix-command'] if _experimental_flag_needed(v) else ['nix']
+
+

 def to_Digest16(v: Verification, digest32: Digest32) -> Digest16:
     v.status('Converting digest to base16')
 def to_Digest16(v: Verification, digest32: Digest32) -> Digest16:
     v.status('Converting digest to base16')

-    process = subprocess.run(
-        ['nix', 'to-base16', '--type', 'sha256', digest32], stdout=subprocess.PIPE)
+    process = subprocess.run(_nix_command(v) + [
+        'to-base16',
+        '--type',
+        'sha256',
+        digest32],
+        stdout=subprocess.PIPE)

     v.result(process.returncode == 0)
     return Digest16(process.stdout.decode().strip())
 
 
 def to_Digest32(v: Verification, digest16: Digest16) -> Digest32:
     v.status('Converting digest to base32')
     v.result(process.returncode == 0)
     return Digest16(process.stdout.decode().strip())
 
 
 def to_Digest32(v: Verification, digest16: Digest16) -> Digest32:
     v.status('Converting digest to base32')

-    process = subprocess.run(
-        ['nix', 'to-base32', '--type', 'sha256', digest16], stdout=subprocess.PIPE)
+    process = subprocess.run(_nix_command(v) + [
+        'to-base32',
+        '--type',
+        'sha256',
+        digest16],
+        stdout=subprocess.PIPE)

     v.result(process.returncode == 0)
     return Digest32(process.stdout.decode().strip())
 
     v.result(process.returncode == 0)
     return Digest32(process.stdout.decode().strip())
 


@@ -253,7 +361,7 @@ def fetch_with_nix_prefetch_url(
         v: Verification,
         url: str,
         digest: Digest16) -> str:
         v: Verification,
         url: str,
         digest: Digest16) -> str:

-    v.status('Fetching %s' % url)
+    v.status(f'Fetching {url}')

     process = subprocess.run(
         ['nix-prefetch-url', '--print-path', url, digest], stdout=subprocess.PIPE)
     v.result(process.returncode == 0)
     process = subprocess.run(
         ['nix-prefetch-url', '--print-path', url, digest], stdout=subprocess.PIPE)
     v.result(process.returncode == 0)


@@ -261,308 +369,261 @@ def fetch_with_nix_prefetch_url(
     assert empty == ''
     v.check("Verifying nix-prefetch-url's digest",
             to_Digest16(v, Digest32(prefetch_digest)) == digest)
     assert empty == ''
     v.check("Verifying nix-prefetch-url's digest",
             to_Digest16(v, Digest32(prefetch_digest)) == digest)

-    v.status("Verifying file digest")
+    v.status(f"Verifying digest of {path}")

     file_digest = digest_file(path)
     v.result(file_digest == digest)
     return path  # type: ignore  # (for old mypy)
 
 
     file_digest = digest_file(path)
     v.result(file_digest == digest)
     return path  # type: ignore  # (for old mypy)
 
 

-def fetch_resources(v: Verification, channel: TarrableSearchPath) -> None:
+def fetch_resources(
+        v: Verification,
+        pin: GitPin,
+        forwarded_url: str,
+        table: Dict[str, ChannelTableEntry]) -> None:

     for resource in ['git-revision', 'nixexprs.tar.xz']:
     for resource in ['git-revision', 'nixexprs.tar.xz']:

-        fields = channel.table[resource]
-        fields.absolute_url = urllib.parse.urljoin(
-            channel.forwarded_url, fields.url)
+        fields = table[resource]
+        fields.absolute_url = urllib.parse.urljoin(forwarded_url, fields.url)

         fields.file = fetch_with_nix_prefetch_url(
             v, fields.absolute_url, fields.digest)
     v.status('Verifying git commit on main page matches git commit in table')
         fields.file = fetch_with_nix_prefetch_url(
             v, fields.absolute_url, fields.digest)
     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)
-
-
-def git_cachedir(git_repo: str) -> str:
-    return os.path.join(
-        xdg.XDG_CACHE_HOME,
-        'pinch/git',
-        digest_string(git_repo.encode()))
+    with open(table['git-revision'].file, encoding='utf-8') as rev_file:
+        v.result(rev_file.read(999) == pin.git_revision)

 
 
 
 

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

     return os.path.join(
         xdg.XDG_CACHE_HOME,
         'pinch/git-tarball',
     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))
+        f'{digest_string(channel.git_repo.encode())}-{pin.git_revision}-{pin.release_name}')

 
 
 
 

-def verify_git_ancestry(v: Verification, channel: TarrableSearchPath) -> None:
-    cachedir = git_cachedir(channel.git_repo)
-    v.status('Verifying rev is an ancestor of ref')
+def verify_git_ancestry(
+        v: Verification,
+        channel: TarrableSearchPath,
+        old_revision: str,
+        new_revision: str) -> None:
+    cachedir = git_cache.git_cachedir(channel.git_repo)
+    v.status(f'Verifying rev is an ancestor of previous rev {old_revision}')

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

-                              channel.git_revision,
-                              channel.git_ref])
-    v.result(process.returncode == 0)
-
-    if hasattr(channel, 'old_git_revision'):
-        v.status(
-            'Verifying rev is an ancestor of previous rev %s' %
-            channel.old_git_revision)
-        process = subprocess.run(['git',
-                                  '-C',
-                                  cachedir,
-                                  'merge-base',
-                                  '--is-ancestor',
-                                  channel.old_git_revision,
-                                  channel.git_revision])
-        v.result(process.returncode == 0)
-
-
-def git_fetch(v: Verification, channel: TarrableSearchPath) -> None:
-    # 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
-    # details for my comfort.  So we re-implement here half of nix.fetchGit.
-    # :(
-
-    cachedir = git_cachedir(channel.git_repo)
-    if not os.path.exists(cachedir):
-        v.status("Initializing git repo")
-        process = subprocess.run(
-            ['git', 'init', '--bare', cachedir])
-        v.result(process.returncode == 0)
-
-    v.status('Fetching ref "%s" from %s' % (channel.git_ref, channel.git_repo))
-    # We don't use --force here because we want to abort and freak out if forced
-    # updates are happening.
-    process = subprocess.run(['git',
-                              '-C',
-                              cachedir,
-                              'fetch',
-                              channel.git_repo,
-                              '%s:%s' % (channel.git_ref,
-                                         channel.git_ref)])
+                              old_revision,
+                              new_revision])

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

-    if hasattr(channel, 'git_revision'):
-        v.status('Verifying that fetch retrieved this rev')
-        process = subprocess.run(
-            ['git', '-C', cachedir, 'cat-file', '-e', channel.git_revision])
-        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)
-

 
 

-def ensure_git_rev_available(
-        v: Verification,
-        channel: TarrableSearchPath) -> None:
-    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])
-        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)
-            return
-    git_fetch(v, channel)
+def broken_symlinks_are_identical(root1: str, root2: str, path: str) -> bool:
+    a = os.path.join(root1, path)
+    b = os.path.join(root2, path)
+    return (os.path.islink(a)
+            and os.path.islink(b)
+            and not os.path.exists(a)
+            and not os.path.exists(b)
+            and os.readlink(a) == os.readlink(b))

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

-        channel: TarrableSearchPath,
+        pin: GitPin,

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

     v.ok()
     v.ok()

-    v.check('%d files match' % len(match), len(match) > 0)
-    v.check('%d files differ' % len(mismatch), len(mismatch) == 0)
+    v.check(f'{len(match)} files match', len(match) > 0)
+    v.check(f'{len(mismatch)} files differ', len(mismatch) == 0)

     expected_errors = [
         '.git-revision',
         '.version-suffix',
         'nixpkgs',
         'programs.sqlite',
         'svn-revision']
     expected_errors = [
         '.git-revision',
         '.version-suffix',
         'nixpkgs',
         'programs.sqlite',
         'svn-revision']

-    benign_errors = []
+    benign_expected_errors = []

     for ee in expected_errors:
         if ee in errors:
             errors.remove(ee)
     for ee in expected_errors:
         if ee in errors:
             errors.remove(ee)

-            benign_errors.append(ee)
+            benign_expected_errors.append(ee)
+    errors = [
+        e for e in errors
+        if not broken_symlinks_are_identical(tarball_contents, git_contents, e)
+    ]

     v.check(
     v.check(

-        '%d unexpected incomparable files' %
-        len(errors),
+        f'{len(errors)} unexpected incomparable files: {errors}',

         len(errors) == 0)
     v.check(
         len(errors) == 0)
     v.check(

-        '(%d of %d expected incomparable files)' %
-        (len(benign_errors),
-         len(expected_errors)),
-        len(benign_errors) == len(expected_errors))
+        f'({len(benign_expected_errors)} of {len(expected_errors)} expected incomparable files)',
+        len(benign_expected_errors) == len(expected_errors))

 
 
 def extract_tarball(
         v: Verification,
 
 
 def extract_tarball(
         v: Verification,

-        channel: TarrableSearchPath,
+        table: Dict[str, ChannelTableEntry],

         dest: str) -> None:
         dest: str) -> None:

-    v.status('Extracting tarball %s' %
-             channel.table['nixexprs.tar.xz'].file)
-    shutil.unpack_archive(
-        channel.table['nixexprs.tar.xz'].file,
-        dest)
+    v.status(f"Extracting tarball {table['nixexprs.tar.xz'].file}")
+    shutil.unpack_archive(table['nixexprs.tar.xz'].file, dest)

     v.ok()
 
 
 def git_checkout(
         v: Verification,
         channel: TarrableSearchPath,
     v.ok()
 
 
 def git_checkout(
         v: Verification,
         channel: TarrableSearchPath,

+        pin: GitPin,

         dest: str) -> None:
     v.status('Checking out corresponding git revision')
         dest: str) -> None:
     v.status('Checking out corresponding git revision')

-    git = subprocess.Popen(['git',
-                            '-C',
-                            git_cachedir(channel.git_repo),
-                            'archive',
-                            channel.git_revision],
-                           stdout=subprocess.PIPE)
-    tar = subprocess.Popen(
-        ['tar', 'x', '-C', dest, '-f', '-'], stdin=git.stdout)
-    if git.stdout:
-        git.stdout.close()
-    tar.wait()
-    git.wait()
-    v.result(git.returncode == 0 and tar.returncode == 0)
-
-
-def git_get_tarball(v: Verification, channel: TarrableSearchPath) -> str:
-    cache_file = tarball_cache_file(channel)
+    with subprocess.Popen(
+            ['git', '-C', git_cache.git_cachedir(channel.git_repo), 'archive', pin.git_revision],
+            stdout=subprocess.PIPE) as git:
+        with subprocess.Popen(['tar', 'x', '-C', dest, '-f', '-'], stdin=git.stdout) as tar:
+            if git.stdout:
+                git.stdout.close()
+            tar.wait()
+            git.wait()
+            v.result(git.returncode == 0 and tar.returncode == 0)
+
+
+def git_get_tarball(
+        v: Verification,
+        channel: TarrableSearchPath,
+        pin: GitPin) -> str:
+    cache_file = tarball_cache_file(channel, pin)

     if os.path.exists(cache_file):
     if os.path.exists(cache_file):

-        cached_tarball = open(cache_file).read(9999)
-        if os.path.exists(cached_tarball):
-            return cached_tarball
+        with open(cache_file, encoding='utf-8') as f:
+            cached_tarball = f.read(9999)
+            if os.path.exists(cached_tarball):
+                return cached_tarball

 
     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')
-        with open(output_filename, 'w') as output_file:
-            v.status(
-                'Generating tarball for git revision %s' %
-                channel.git_revision)
-            git = subprocess.Popen(['git',
-                                    '-C',
-                                    git_cachedir(channel.git_repo),
-                                    'archive',
-                                    '--prefix=%s/' % channel.release_name,
-                                    channel.git_revision],
-                                   stdout=subprocess.PIPE)
-            xz = subprocess.Popen(['xz'], stdin=git.stdout, stdout=output_file)
-            xz.wait()
-            git.wait()
-            v.result(git.returncode == 0 and xz.returncode == 0)
-
-        v.status('Putting tarball in Nix store')
-        process = subprocess.run(
-            ['nix-store', '--add', output_filename], stdout=subprocess.PIPE)
-        v.result(process.returncode == 0)
-        store_tarball = process.stdout.decode().strip()
+            output_dir, pin.release_name + '.tar.xz')
+        with open(output_filename, 'w', encoding='utf-8') as output_file:
+            v.status(f'Generating tarball for git revision {pin.git_revision}')
+            with subprocess.Popen(
+                    ['git', '-C', git_cache.git_cachedir(channel.git_repo),
+                        'archive', f'--prefix={pin.release_name}/', pin.git_revision],
+                    stdout=subprocess.PIPE) as git:
+                with subprocess.Popen(['xz'], stdin=git.stdout, stdout=output_file) as xz:
+                    xz.wait()
+                    git.wait()
+                    v.result(git.returncode == 0 and xz.returncode == 0)
+
+        store_tarball = copy_to_nix_store(v, output_filename)

 
         os.makedirs(os.path.dirname(cache_file), exist_ok=True)
 
         os.makedirs(os.path.dirname(cache_file), exist_ok=True)

-        open(cache_file, 'w').write(store_tarball)
+        with open(cache_file, 'w', encoding='utf-8') as f:
+            f.write(store_tarball)

         return store_tarball  # type: ignore  # (for old mypy)
 
 
 def check_channel_metadata(
         v: Verification,
         return store_tarball  # type: ignore  # (for old mypy)
 
 
 def check_channel_metadata(
         v: Verification,

-        channel: TarrableSearchPath,
+        pin: GitPin,

         channel_contents: str) -> None:
     v.status('Verifying git commit in channel tarball')
         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)
+    with open(os.path.join(channel_contents, pin.release_name, '.git-revision'),
+              encoding='utf-8') as f:
+        v.result(f.read(999) == pin.git_revision)

 
     v.status(
 
     v.status(

-        'Verifying version-suffix is a suffix of release name %s:' %
-        channel.release_name)
-    version_suffix = open(
-        os.path.join(
-            channel_contents,
-            channel.release_name,
-            '.version-suffix')).read(999)
+        f'Verifying version-suffix is a suffix of release name {pin.release_name}:')
+    with open(os.path.join(channel_contents, pin.release_name, '.version-suffix'),
+              encoding='utf-8') as f:
+        version_suffix = f.read(999)

     v.status(version_suffix)
     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,
 
 
 def check_channel_contents(
         v: Verification,

-        channel: TarrableSearchPath) -> None:
+        channel: TarrableSearchPath,
+        table: Dict[str, ChannelTableEntry],
+        pin: GitPin) -> None:

     with tempfile.TemporaryDirectory() as channel_contents, \
             tempfile.TemporaryDirectory() as git_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)
+        extract_tarball(v, table, 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: TarrableSearchPath) -> 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: TarrableSearchPath) -> 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',

-                              git_cachedir(channel.git_repo),
+                              git_cache.git_cachedir(channel.git_repo),

                               'log',
                               '-n1',
                               '--format=%ct-%h',
                               '--abbrev=11',
                               '--no-show-signature',
                               'log',
                               '-n1',
                               '--format=%ct-%h',
                               '--abbrev=11',
                               '--no-show-signature',

-                              channel.git_revision],
+                              git_revision],

                              stdout=subprocess.PIPE)
     v.result(process.returncode == 0 and process.stdout != b'')
                              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())
+    return f'{os.path.basename(channel.git_repo)}-{process.stdout.decode().strip()}'
+
+
+K = TypeVar('K')
+V = TypeVar('V')
+
+
+def partition_dict(pred: Callable[[K, V], bool],
+                   d: Dict[K, V]) -> Tuple[Dict[K, V], Dict[K, V]]:
+    selected: Dict[K, V] = {}
+    remaining: Dict[K, V] = {}
+    for k, v in d.items():
+        if pred(k, v):
+            selected[k] = v
+        else:
+            remaining[k] = v
+    return selected, remaining
+
+
+def filter_dict(d: Dict[K, V], fields: Set[K]
+                ) -> Tuple[Dict[K, V], Dict[K, V]]:
+    return partition_dict(lambda k, v: k in fields, d)

 
 
 
 

-def read_search_path(conf: configparser.SectionProxy) -> SearchPath:
-    if 'alias_of' in conf:
-        return AliasSearchPath(**dict(conf.items()))
-    if 'channel_url' in conf:
-        return ChannelSearchPath(**dict(conf.items()))
-    return GitSearchPath(**dict(conf.items()))
+def read_config_section(
+        conf: configparser.SectionProxy) -> Tuple[SearchPath, Optional[Pin]]:
+    mapping: Mapping[str, Tuple[Type[SearchPath], Type[Pin]]] = {
+        'alias': (AliasSearchPath, AliasPin),
+        'channel': (ChannelSearchPath, ChannelPin),
+        'git': (GitSearchPath, GitPin),
+        'symlink': (SymlinkSearchPath, SymlinkPin),
+    }
+    SP, P = mapping[conf['type']]
+    _, all_fields = filter_dict(dict(conf.items()), set(['type']))
+    pin_fields, remaining_fields = filter_dict(all_fields, set(P._fields))
+    # Error suppression works around https://github.com/python/mypy/issues/9007
+    pin_present = pin_fields or P._fields == ()
+    pin = P(**pin_fields) if pin_present else None  # type: ignore
+    return SP(**remaining_fields), pin
+
+
+def read_pinned_config_section(
+        section: str, conf: configparser.SectionProxy) -> Tuple[SearchPath, Pin]:
+    sp, pin = read_config_section(conf)
+    if pin is None:
+        raise RuntimeError(
+            f'Cannot update unpinned channel "{section}" (Run "pin" before "update")')
+    return sp, pin

 
 
 def read_config(filename: str) -> configparser.ConfigParser:
     config = configparser.ConfigParser()
 
 
 def read_config(filename: str) -> configparser.ConfigParser:
     config = configparser.ConfigParser()

-    config.read_file(open(filename), filename)
+    with open(filename, encoding='utf-8') as f:
+        config.read_file(f, filename)

     return config
 
 
     return config
 
 


@@ -573,54 +634,66 @@ def read_config_files(
         config = read_config(file)
         for section in config.sections():
             if section in merged_config:
         config = read_config(file)
         for section in config.sections():
             if section in merged_config:

-                raise Exception('Duplicate channel "%s"' % section)
+                raise RuntimeError('Duplicate channel "{section}"')

             merged_config[section] = config[section]
     return merged_config
 
 
             merged_config[section] = config[section]
     return merged_config
 
 

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

-        sp = read_search_path(config[section])
+        sp, old_pin = read_config_section(config[section])

 
 

-        sp.pin(v, config[section])
+        config[section].update(sp.pin(v, old_pin)._asdict())

 
 

-    with open(args.channels_file, 'w') as configfile:
+    with open(args.channels_file, 'w', encoding='utf-8') as configfile:

         config.write(configfile)
 
 
         config.write(configfile)
 
 

-def update(args: argparse.Namespace) -> None:
+def updateCommand(args: argparse.Namespace) -> None:

     v = Verification()
     exprs: Dict[str, str] = {}
     v = Verification()
     exprs: Dict[str, str] = {}

-    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])
+    profile_manifest = os.path.join(args.profile, "manifest.nix")
+    search_paths: List[str] = [
+        "-I", "pinch_profile=" + args.profile,
+        "-I", "pinch_profile_manifest=" + os.readlink(profile_manifest)
+    ] if os.path.exists(profile_manifest) else []
+    config = {
+        section: read_pinned_config_section(section, conf) for section,
+        conf in read_config_files(
+            args.channels_file).items()}
+    alias, nonalias = partition_dict(
+        lambda k, v: isinstance(v[0], AliasSearchPath), config)
+
+    for section, (sp, pin) in sorted(nonalias.items()):
+        assert not isinstance(sp, AliasSearchPath)  # mypy can't see through
+        assert not isinstance(pin, AliasPin)        # partition_dict()
+        tarball = sp.fetch(v, pin)
+        search_paths.extend(
+            ["-I", f"pinch_tarball_for_{pin.release_name}={tarball}"])

         exprs[section] = (
         exprs[section] = (

-            'f: f { name = "%s"; channelName = "%%s"; src = builtins.storePath "%s"; }' %
-            (config[section]['release_name'], tarball))
+            f'f: f {{ name = "{pin.release_name}"; channelName = "%s"; '
+            f'src = builtins.storePath "{tarball}"; }}')

 
 

-    for section in config:
-        if 'alias_of' in config[section]:
-            exprs[section] = exprs[str(config[section]['alias_of'])]
+    for section, (sp, pin) in alias.items():
+        assert isinstance(sp, AliasSearchPath)  # For mypy
+        exprs[section] = exprs[sp.alias_of]

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

-        '/nix/var/nix/profiles/per-user/%s/channels' %
-        getpass.getuser(),
+        args.profile,

         '--show-trace',
         '--file',
         '<nix/unpack-channel.nix>',
         '--install',
         '--show-trace',
         '--file',
         '<nix/unpack-channel.nix>',
         '--install',

-        '--from-expression'] + [exprs[name] % name for name in sorted(exprs.keys())]
+        '--remove-all',
+    ] + search_paths + ['--from-expression'] + [
+        exprs[name] % name for name in sorted(exprs.keys())]

     if args.dry_run:
         print(' '.join(map(shlex.quote, command)))
     else:
     if args.dry_run:
         print(' '.join(map(shlex.quote, command)))
     else:


@@ -635,11 +708,13 @@ 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 = subparsers.add_parser('update')
     parser_update.add_argument('--dry-run', action='store_true')

+    parser_update.add_argument('--profile', default=(
+        f'/nix/var/nix/profiles/per-user/{getpass.getuser()}/channels'))

     parser_update.add_argument('channels_file', type=str, nargs='+')
     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)