]> git.scottworley.com Git - pinch/blobdiff - pinch.py
Release 3.0.1
[pinch] / pinch.py
index 916739d32797d6179f4ebdf553abeeb69b354f8f..5eb76018e710025a01bf632b1ab3234a79153815 100644 (file)
--- a/pinch.py
+++ b/pinch.py
@@ -1,4 +1,3 @@
-from abc import ABC, abstractmethod
 import argparse
 import configparser
 import filecmp
@@ -12,6 +11,7 @@ import shlex
 import shutil
 import subprocess
 import sys
+import tarfile
 import tempfile
 import types
 import urllib.parse
@@ -19,6 +19,7 @@ import urllib.request
 import xml.dom.minidom
 
 from typing import (
+    Callable,
     Dict,
     Iterable,
     List,
@@ -26,15 +27,19 @@ from typing import (
     NamedTuple,
     NewType,
     Optional,
+    Set,
     Tuple,
     Type,
+    TypeVar,
     Union,
 )
 
+import git_cache
+
 # Use xdg module when it's less painful to have as a dependency
 
 
-class XDG(types.SimpleNamespace):
+class XDG(NamedTuple):
     XDG_CACHE_HOME: str
 
 
@@ -95,6 +100,12 @@ class AliasPin(NamedTuple):
     pass
 
 
+class SymlinkPin(NamedTuple):
+    @property
+    def release_name(self) -> str:
+        return 'link'
+
+
 class GitPin(NamedTuple):
     git_revision: str
     release_name: str
@@ -107,90 +118,103 @@ class ChannelPin(NamedTuple):
     tarball_sha256: str
 
 
-Pin = Union[AliasPin, GitPin, ChannelPin]
+Pin = Union[AliasPin, SymlinkPin, GitPin, ChannelPin]
 
 
-class SearchPath(types.SimpleNamespace, ABC):
+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) -> Pin:
-        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
 
-    def pin(self, v: Verification) -> AliasPin:
-        assert not hasattr(self, 'git_repo')
+    # pylint: disable=no-self-use
+    def pin(self, _: Verification, __: Optional[Pin]) -> AliasPin:
         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 SymlinkSearchPath(NamedTuple):
+    path: str
+
+    # pylint: disable=no-self-use
+    def pin(self, _: Verification, __: Optional[Pin]) -> SymlinkPin:
+        return SymlinkPin()
 
+    def fetch(self, v: Verification, _: Pin) -> str:
+        return symlink_archive(v, self.path)
 
-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)
+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)
 
-    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)
+    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(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=self.table['nixexprs.tar.xz'].absolute_url,
-            tarball_sha256=self.table['nixexprs.tar.xz'].digest,
-            git_revision=self.git_revision)
+            tarball_url=table['nixexprs.tar.xz'].absolute_url,
+            tarball_sha256=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)
+    def fetch(self, v: Verification, pin: Pin) -> str:
+        assert isinstance(pin, ChannelPin)
 
         return fetch_with_nix_prefetch_url(
-            v, conf['tarball_url'], Digest16(
-                conf['tarball_sha256']))
+            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]]:
@@ -221,18 +245,21 @@ def compare(a: str, b: str) -> Tuple[List[str], List[str], List[str]]:
     return filecmp.cmpfiles(a, b, files, shallow=False)
 
 
-def fetch(v: Verification, channel: TarrableSearchPath) -> None:
+def fetch_channel(
+        v: Verification, channel: ChannelSearchPath) -> Tuple[str, str]:
     v.status('Fetching channel')
     request = urllib.request.urlopen(channel.channel_url, timeout=10)
-    channel.channel_html = request.read()
-    channel.forwarded_url = request.geturl()
+    channel_html = request.read().decode()
+    forwarded_url = request.geturl()
     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 != forwarded_url)
+    return channel_html, forwarded_url
 
 
-def parse_channel(v: Verification, channel: TarrableSearchPath) -> GitPin:
+def parse_channel(v: Verification, channel_html: str) \
+        -> Tuple[Dict[str, ChannelTableEntry], GitPin]:
     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.status('Extracting release name:')
@@ -244,23 +271,22 @@ def parse_channel(v: Verification, channel: TarrableSearchPath) -> GitPin:
 
     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.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)
-        channel.table[name] = ChannelTableEntry(
-            url=url, digest=digest, size=size)
+        table[name] = ChannelTableEntry(url=url, digest=digest, size=size)
     v.ok()
-    return GitPin(release_name=title_name, git_revision=channel.git_revision)
+    return table, GitPin(release_name=title_name, git_revision=git_revision)
 
 
 def digest_string(s: bytes) -> Digest16:
@@ -312,25 +338,16 @@ def fetch_with_nix_prefetch_url(
 
 def fetch_resources(
         v: Verification,
-        channel: ChannelSearchPath,
-        pin: GitPin) -> None:
+        pin: GitPin,
+        forwarded_url: str,
+        table: Dict[str, ChannelTableEntry]) -> None:
     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')
-    v.result(
-        open(
-            channel.table['git-revision'].file).read(999) == pin.git_revision)
-
-
-def git_cachedir(git_repo: str) -> str:
-    return os.path.join(
-        xdg.XDG_CACHE_HOME,
-        'pinch/git',
-        digest_string(git_repo.encode()))
+    v.result(open(table['git-revision'].file).read(999) == pin.git_revision)
 
 
 def tarball_cache_file(channel: TarrableSearchPath, pin: GitPin) -> str:
@@ -346,110 +363,28 @@ def tarball_cache_file(channel: TarrableSearchPath, pin: GitPin) -> str:
 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')
+        old_revision: str,
+        new_revision: str) -> None:
+    cachedir = git_cache.git_cachedir(channel.git_repo)
+    v.status('Verifying rev is an ancestor of previous rev %s' % old_revision)
     process = subprocess.run(['git',
                               '-C',
                               cachedir,
                               'merge-base',
                               '--is-ancestor',
-                              new_revision,
-                              channel.git_ref])
-    v.result(process.returncode == 0)
-
-    if old_revision is not None:
-        v.status(
-            'Verifying rev is an ancestor of previous rev %s' %
-            old_revision)
-        process = subprocess.run(['git',
-                                  '-C',
-                                  cachedir,
-                                  'merge-base',
-                                  '--is-ancestor',
-                                  old_revision,
-                                  new_revision])
-        v.result(process.returncode == 0)
-
-
-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
-    # 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)
 
-    if desired_revision is not None:
-        v.status('Verifying that fetch retrieved this rev')
-        process = subprocess.run(
-            ['git', '-C', cachedir, 'cat-file', '-e', desired_revision])
-        v.result(process.returncode == 0)
-
-    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: 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(
-            ['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:
-            verify_git_ancestry(v, channel, pin.git_revision, old_revision)
-            return
-    git_fetch(v, channel, pin.git_revision, old_revision)
-
 
 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')
     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)
@@ -477,26 +412,24 @@ def compare_tarball_and_git(
 
 def extract_tarball(
         v: Verification,
-        channel: TarrableSearchPath,
+        table: Dict[str, ChannelTableEntry],
         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('Extracting tarball %s' % table['nixexprs.tar.xz'].file)
+    shutil.unpack_archive(table['nixexprs.tar.xz'].file, dest)
     v.ok()
 
 
 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),
+                            git_cache.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)
@@ -526,7 +459,7 @@ def git_get_tarball(
                 pin.git_revision)
             git = subprocess.Popen(['git',
                                     '-C',
-                                    git_cachedir(channel.git_repo),
+                                    git_cache.git_cachedir(channel.git_repo),
                                     'archive',
                                     '--prefix=%s/' % pin.release_name,
                                     pin.git_revision],
@@ -536,11 +469,7 @@ def git_get_tarball(
             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()
+        store_tarball = copy_to_nix_store(v, output_filename)
 
         os.makedirs(os.path.dirname(cache_file), exist_ok=True)
         open(cache_file, 'w').write(store_tarball)
@@ -549,40 +478,42 @@ def git_get_tarball(
 
 def check_channel_metadata(
         v: Verification,
-        channel: TarrableSearchPath,
+        pin: GitPin,
         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:' %
-        channel.release_name)
+        pin.release_name)
     version_suffix = open(
         os.path.join(
             channel_contents,
-            channel.release_name,
+            pin.release_name,
             '.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: TarrableSearchPath) -> None:
+        channel: TarrableSearchPath,
+        table: Dict[str, ChannelTableEntry],
+        pin: GitPin) -> None:
     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()
@@ -595,7 +526,7 @@ def git_revision_name(
     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',
@@ -608,13 +539,52 @@ def git_revision_name(
                       process.stdout.decode().strip())
 
 
-def read_search_path(conf: configparser.SectionProxy) -> SearchPath:
-    mapping: Mapping[str, Type[SearchPath]] = {
-        'alias': AliasSearchPath,
-        'channel': ChannelSearchPath,
-        'git': GitSearchPath,
+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_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),
     }
-    return mapping[conf['type']](**dict(conf.items()))
+    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 Exception(
+            'Cannot update unpinned channel "%s" (Run "pin" before "update")' %
+            section)
+    return sp, pin
 
 
 def read_config(filename: str) -> configparser.ConfigParser:
@@ -642,9 +612,9 @@ def pinCommand(args: argparse.Namespace) -> None:
         if args.channels and section not in args.channels:
             continue
 
-        sp = read_search_path(config[section])
+        sp, old_pin = read_config_section(config[section])
 
-        config[section].update(sp.pin(v)._asdict())
+        config[section].update(sp.pin(v, old_pin)._asdict())
 
     with open(args.channels_file, 'w') as configfile:
         config.write(configfile)
@@ -653,26 +623,29 @@ def pinCommand(args: argparse.Namespace) -> None:
 def updateCommand(args: argparse.Namespace) -> None:
     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])
+    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 nonalias.items():
+        assert not isinstance(sp, AliasSearchPath)  # mypy can't see through
+        assert not isinstance(pin, AliasPin)        # partition_dict()
+        tarball = sp.fetch(v, pin)
         exprs[section] = (
             'f: f { name = "%s"; channelName = "%%s"; src = builtins.storePath "%s"; }' %
-            (config[section]['release_name'], tarball))
+            (pin.release_name, 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',
-        '/nix/var/nix/profiles/per-user/%s/channels' %
-        getpass.getuser(),
+        args.profile,
         '--show-trace',
         '--file',
         '<nix/unpack-channel.nix>',
@@ -695,6 +668,8 @@ def main() -> None:
     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('--profile', default=(
+        '/nix/var/nix/profiles/per-user/%s/channels' % getpass.getuser()))
     parser_update.add_argument('channels_file', type=str, nargs='+')
     parser_update.set_defaults(func=updateCommand)
     args = parser.parse_args()