feat(pre-commit): Add binary based install

For no additional build dependencies (besides Python >= 3.6), and faster
install.

The setup.py here is a copy of the one at
https://github.com/shellcheck-py/shellcheck-py with changes kept at the
bare minimum for future diffability.

We don't support checksumming at least yet, because there's no access to
them from cargo-release at the moment.

Closes #285

.pre-commit-hooks.yaml

@@ -1,6 +1,14 @@
 - id: typos
   name: typos
-  description: Source code spell checker
+  description: Source code spell checker, binary install
+  language: python
+  entry: typos
+  args: [--write-changes]
+  types: [text]
+
+- id: typos-src
+  name: typos
+  description: Source code spell checker, source install
   language: rust
   entry: typos
   args: [--write-changes]

docs/pre-commit.md

@@ -11,6 +11,10 @@ repos:
       - id: typos
 ```
 
+The `typos` id installs a prebuilt executable from GitHub releases. If
+one does not exist for the target platform, or if one built from
+sources is preferred, use `typos-src` as the hook id instead.
+
 Be sure to change `rev` to use the desired `typos` git tag or
 revision.
 

setup.py

@@ -0,0 +1,166 @@
+#!/usr/bin/env python3
+import hashlib
+import http
+import io
+import os.path
+import stat
+import sys
+import tarfile
+import urllib.request
+import zipfile
+from distutils.command.build import build as orig_build
+from distutils.core import Command
+from typing import Tuple
+
+from setuptools import setup
+from setuptools.command.install import install as orig_install
+
+TYPOS_VERSION = '1.0.9'
+POSTFIX_SHA256 = {
+    'linux': (
+        'x86_64-unknown-linux-gnu.tar.gz',
+        '',  # TODO: sha256 hexhash when we can generate it with release
+    ),
+    'darwin': (
+        'x86_64-apple-darwin.tar.gz',
+        '',  # TODO: sha256 hexhash when we can generate it with release
+    ),
+    'win32': (
+        'x86_64-pc-windows-msvc.zip',
+        '',  # TODO: sha256 hexhash when we can generate it with release
+    ),
+}
+PY_VERSION = '1'
+
+
+def get_download_url() -> Tuple[str, str]:
+    postfix, sha256 = POSTFIX_SHA256[sys.platform]
+    url = (
+        f'https://github.com/crate-ci/typos/releases/download/'
+        f'v{TYPOS_VERSION}/typos-v{TYPOS_VERSION}-{postfix}'
+    )
+    return url, sha256
+
+
+def download(url: str, sha256: str) -> bytes:
+    with urllib.request.urlopen(url) as resp:
+        code = resp.getcode()
+        if code != http.HTTPStatus.OK:
+            raise ValueError(f'HTTP failure. Code: {code}')
+        data = resp.read()
+
+    if not sha256:
+        return data
+
+    checksum = hashlib.sha256(data).hexdigest()
+    if checksum != sha256:
+        raise ValueError(f'sha256 mismatch, expected {sha256}, got {checksum}')
+
+    return data
+
+
+def extract(url: str, data: bytes) -> bytes:
+    with io.BytesIO(data) as bio:
+        if '.tar.' in url:
+            with tarfile.open(fileobj=bio) as tarf:
+                for info in tarf.getmembers():
+                    if info.isfile() and info.name.endswith('typos'):
+                        return tarf.extractfile(info).read()
+        elif url.endswith('.zip'):
+            with zipfile.ZipFile(bio) as zipf:
+                for info in zipf.infolist():
+                    if info.filename.endswith('.exe'):
+                        return zipf.read(info.filename)
+
+    raise AssertionError(f'unreachable {url}')
+
+
+def save_executable(data: bytes, base_dir: str):
+    exe = 'typos' if sys.platform != 'win32' else 'typos.exe'
+    output_path = os.path.join(base_dir, exe)
+    os.makedirs(base_dir)
+
+    with open(output_path, 'wb') as fp:
+        fp.write(data)
+
+    # Mark as executable.
+    # https://stackoverflow.com/a/14105527
+    mode = os.stat(output_path).st_mode
+    mode |= stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH
+    os.chmod(output_path, mode)
+
+
+class build(orig_build):
+    sub_commands = orig_build.sub_commands + [('fetch_binaries', None)]
+
+
+class install(orig_install):
+    sub_commands = orig_install.sub_commands + [('install_typos', None)]
+
+
+class fetch_binaries(Command):
+    build_temp = None
+
+    def initialize_options(self):
+        pass
+
+    def finalize_options(self):
+        self.set_undefined_options('build', ('build_temp', 'build_temp'))
+
+    def run(self):
+        # save binary to self.build_temp
+        url, sha256 = get_download_url()
+        archive = download(url, sha256)
+        data = extract(url, archive)
+        save_executable(data, self.build_temp)
+
+
+class install_typos(Command):
+    description = 'install the typos executable'
+    outfiles = ()
+    build_dir = install_dir = None
+
+    def initialize_options(self):
+        pass
+
+    def finalize_options(self):
+        # this initializes attributes based on other commands' attributes
+        self.set_undefined_options('build', ('build_temp', 'build_dir'))
+        self.set_undefined_options(
+            'install', ('install_scripts', 'install_dir'),
+        )
+
+    def run(self):
+        self.outfiles = self.copy_tree(self.build_dir, self.install_dir)
+
+    def get_outputs(self):
+        return self.outfiles
+
+
+command_overrides = {
+    'install': install,
+    'install_typos': install_typos,
+    'build': build,
+    'fetch_binaries': fetch_binaries,
+}
+
+
+try:
+    from wheel.bdist_wheel import bdist_wheel as orig_bdist_wheel
+except ImportError:
+    pass
+else:
+    class bdist_wheel(orig_bdist_wheel):
+        def finalize_options(self):
+            orig_bdist_wheel.finalize_options(self)
+            # Mark us as not a pure python package
+            self.root_is_pure = False
+
+        def get_tag(self):
+            _, _, plat = orig_bdist_wheel.get_tag(self)
+            # We don't contain any python source, nor any python extensions
+            return 'py2.py3', 'none', plat
+
+    command_overrides['bdist_wheel'] = bdist_wheel
+
+setup(version=f'{TYPOS_VERSION}.{PY_VERSION}', cmdclass=command_overrides)