Adding upstream version 2.2.0.upstream/2.2.0

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

18 files changed, 1343 insertions, 0 deletions

diff --git a/pre_commit/languages/__init__.py b/pre_commit/languages/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/pre_commit/languages/__init__.py
diff --git a/pre_commit/languages/all.py b/pre_commit/languages/all.py
new file mode 100644
index 0000000..8f4ffa8
--- /dev/null
+++ b/pre_commit/languages/all.py
@@ -0,0 +1,60 @@
+from typing import Callable
+from typing import NamedTuple
+from typing import Optional
+from typing import Sequence
+from typing import Tuple
+
+from pre_commit.hook import Hook
+from pre_commit.languages import conda
+from pre_commit.languages import docker
+from pre_commit.languages import docker_image
+from pre_commit.languages import fail
+from pre_commit.languages import golang
+from pre_commit.languages import node
+from pre_commit.languages import perl
+from pre_commit.languages import pygrep
+from pre_commit.languages import python
+from pre_commit.languages import python_venv
+from pre_commit.languages import ruby
+from pre_commit.languages import rust
+from pre_commit.languages import script
+from pre_commit.languages import swift
+from pre_commit.languages import system
+from pre_commit.prefix import Prefix
+
+
+class Language(NamedTuple):
+    name: str
+    # Use `None` for no installation / environment
+    ENVIRONMENT_DIR: Optional[str]
+    # return a value to replace `'default` for `language_version`
+    get_default_version: Callable[[], str]
+    # return whether the environment is healthy (or should be rebuilt)
+    healthy: Callable[[Prefix, str], bool]
+    # install a repository for the given language and language_version
+    install_environment: Callable[[Prefix, str, Sequence[str]], None]
+    # execute a hook and return the exit code and output
+    run_hook: 'Callable[[Hook, Sequence[str], bool], Tuple[int, bytes]]'
+
+
+# TODO: back to modules + Protocol: https://github.com/python/mypy/issues/5018
+languages = {
+    # BEGIN GENERATED (testing/gen-languages-all)
+    'conda': Language(name='conda', ENVIRONMENT_DIR=conda.ENVIRONMENT_DIR, get_default_version=conda.get_default_version, healthy=conda.healthy, install_environment=conda.install_environment, run_hook=conda.run_hook),  # noqa: E501
+    'docker': Language(name='docker', ENVIRONMENT_DIR=docker.ENVIRONMENT_DIR, get_default_version=docker.get_default_version, healthy=docker.healthy, install_environment=docker.install_environment, run_hook=docker.run_hook),  # noqa: E501
+    'docker_image': Language(name='docker_image', ENVIRONMENT_DIR=docker_image.ENVIRONMENT_DIR, get_default_version=docker_image.get_default_version, healthy=docker_image.healthy, install_environment=docker_image.install_environment, run_hook=docker_image.run_hook),  # noqa: E501
+    'fail': Language(name='fail', ENVIRONMENT_DIR=fail.ENVIRONMENT_DIR, get_default_version=fail.get_default_version, healthy=fail.healthy, install_environment=fail.install_environment, run_hook=fail.run_hook),  # noqa: E501
+    'golang': Language(name='golang', ENVIRONMENT_DIR=golang.ENVIRONMENT_DIR, get_default_version=golang.get_default_version, healthy=golang.healthy, install_environment=golang.install_environment, run_hook=golang.run_hook),  # noqa: E501
+    'node': Language(name='node', ENVIRONMENT_DIR=node.ENVIRONMENT_DIR, get_default_version=node.get_default_version, healthy=node.healthy, install_environment=node.install_environment, run_hook=node.run_hook),  # noqa: E501
+    'perl': Language(name='perl', ENVIRONMENT_DIR=perl.ENVIRONMENT_DIR, get_default_version=perl.get_default_version, healthy=perl.healthy, install_environment=perl.install_environment, run_hook=perl.run_hook),  # noqa: E501
+    'pygrep': Language(name='pygrep', ENVIRONMENT_DIR=pygrep.ENVIRONMENT_DIR, get_default_version=pygrep.get_default_version, healthy=pygrep.healthy, install_environment=pygrep.install_environment, run_hook=pygrep.run_hook),  # noqa: E501
+    'python': Language(name='python', ENVIRONMENT_DIR=python.ENVIRONMENT_DIR, get_default_version=python.get_default_version, healthy=python.healthy, install_environment=python.install_environment, run_hook=python.run_hook),  # noqa: E501
+    'python_venv': Language(name='python_venv', ENVIRONMENT_DIR=python_venv.ENVIRONMENT_DIR, get_default_version=python_venv.get_default_version, healthy=python_venv.healthy, install_environment=python_venv.install_environment, run_hook=python_venv.run_hook),  # noqa: E501
+    'ruby': Language(name='ruby', ENVIRONMENT_DIR=ruby.ENVIRONMENT_DIR, get_default_version=ruby.get_default_version, healthy=ruby.healthy, install_environment=ruby.install_environment, run_hook=ruby.run_hook),  # noqa: E501
+    'rust': Language(name='rust', ENVIRONMENT_DIR=rust.ENVIRONMENT_DIR, get_default_version=rust.get_default_version, healthy=rust.healthy, install_environment=rust.install_environment, run_hook=rust.run_hook),  # noqa: E501
+    'script': Language(name='script', ENVIRONMENT_DIR=script.ENVIRONMENT_DIR, get_default_version=script.get_default_version, healthy=script.healthy, install_environment=script.install_environment, run_hook=script.run_hook),  # noqa: E501
+    'swift': Language(name='swift', ENVIRONMENT_DIR=swift.ENVIRONMENT_DIR, get_default_version=swift.get_default_version, healthy=swift.healthy, install_environment=swift.install_environment, run_hook=swift.run_hook),  # noqa: E501
+    'system': Language(name='system', ENVIRONMENT_DIR=system.ENVIRONMENT_DIR, get_default_version=system.get_default_version, healthy=system.healthy, install_environment=system.install_environment, run_hook=system.run_hook),  # noqa: E501
+    # END GENERATED
+}
+all_languages = sorted(languages)
diff --git a/pre_commit/languages/conda.py b/pre_commit/languages/conda.py
new file mode 100644
index 0000000..071757a
--- /dev/null
+++ b/pre_commit/languages/conda.py
@@ -0,0 +1,84 @@
+import contextlib
+import os
+from typing import Generator
+from typing import Sequence
+from typing import Tuple
+
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import PatchesT
+from pre_commit.envcontext import SubstitutionT
+from pre_commit.envcontext import UNSET
+from pre_commit.envcontext import Var
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+from pre_commit.prefix import Prefix
+from pre_commit.util import clean_path_on_failure
+from pre_commit.util import cmd_output_b
+
+ENVIRONMENT_DIR = 'conda'
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+
+
+def get_env_patch(env: str) -> PatchesT:
+    # On non-windows systems executable live in $CONDA_PREFIX/bin, on Windows
+    # they can be in $CONDA_PREFIX/bin, $CONDA_PREFIX/Library/bin,
+    # $CONDA_PREFIX/Scripts and $CONDA_PREFIX. Whereas the latter only
+    # seems to be used for python.exe.
+    path: SubstitutionT = (os.path.join(env, 'bin'), os.pathsep, Var('PATH'))
+    if os.name == 'nt':  # pragma: no cover (platform specific)
+        path = (env, os.pathsep, *path)
+        path = (os.path.join(env, 'Scripts'), os.pathsep, *path)
+        path = (os.path.join(env, 'Library', 'bin'), os.pathsep, *path)
+
+    return (
+        ('PYTHONHOME', UNSET),
+        ('VIRTUAL_ENV', UNSET),
+        ('CONDA_PREFIX', env),
+        ('PATH', path),
+    )
+
+
+@contextlib.contextmanager
+def in_env(
+        prefix: Prefix,
+        language_version: str,
+) -> Generator[None, None, None]:
+    directory = helpers.environment_dir(ENVIRONMENT_DIR, language_version)
+    envdir = prefix.path(directory)
+    with envcontext(get_env_patch(envdir)):
+        yield
+
+
+def install_environment(
+        prefix: Prefix,
+        version: str,
+        additional_dependencies: Sequence[str],
+) -> None:
+    helpers.assert_version_default('conda', version)
+    directory = helpers.environment_dir(ENVIRONMENT_DIR, version)
+
+    env_dir = prefix.path(directory)
+    with clean_path_on_failure(env_dir):
+        cmd_output_b(
+            'conda', 'env', 'create', '-p', env_dir, '--file',
+            'environment.yml', cwd=prefix.prefix_dir,
+        )
+        if additional_dependencies:
+            cmd_output_b(
+                'conda', 'install', '-p', env_dir, *additional_dependencies,
+                cwd=prefix.prefix_dir,
+            )
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:
+    # TODO: Some rare commands need to be run using `conda run` but mostly we
+    #       can run them withot which is much quicker and produces a better
+    #       output.
+    # cmd = ('conda', 'run', '-p', env_dir) + hook.cmd
+    with in_env(hook.prefix, hook.language_version):
+        return helpers.run_xargs(hook, hook.cmd, file_args, color=color)
diff --git a/pre_commit/languages/docker.py b/pre_commit/languages/docker.py
new file mode 100644
index 0000000..f449584
--- /dev/null
+++ b/pre_commit/languages/docker.py
@@ -0,0 +1,114 @@
+import hashlib
+import os
+from typing import Sequence
+from typing import Tuple
+
+import pre_commit.constants as C
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+from pre_commit.prefix import Prefix
+from pre_commit.util import CalledProcessError
+from pre_commit.util import clean_path_on_failure
+from pre_commit.util import cmd_output_b
+
+ENVIRONMENT_DIR = 'docker'
+PRE_COMMIT_LABEL = 'PRE_COMMIT'
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+
+
+def md5(s: str) -> str:  # pragma: win32 no cover
+    return hashlib.md5(s.encode()).hexdigest()
+
+
+def docker_tag(prefix: Prefix) -> str:  # pragma: win32 no cover
+    md5sum = md5(os.path.basename(prefix.prefix_dir)).lower()
+    return f'pre-commit-{md5sum}'
+
+
+def docker_is_running() -> bool:  # pragma: win32 no cover
+    try:
+        cmd_output_b('docker', 'ps')
+    except CalledProcessError:
+        return False
+    else:
+        return True
+
+
+def assert_docker_available() -> None:  # pragma: win32 no cover
+    assert docker_is_running(), (
+        'Docker is either not running or not configured in this environment'
+    )
+
+
+def build_docker_image(
+        prefix: Prefix,
+        *,
+        pull: bool,
+) -> None:  # pragma: win32 no cover
+    cmd: Tuple[str, ...] = (
+        'docker', 'build',
+        '--tag', docker_tag(prefix),
+        '--label', PRE_COMMIT_LABEL,
+    )
+    if pull:
+        cmd += ('--pull',)
+    # This must come last for old versions of docker.  See #477
+    cmd += ('.',)
+    helpers.run_setup_cmd(prefix, cmd)
+
+
+def install_environment(
+        prefix: Prefix, version: str, additional_dependencies: Sequence[str],
+) -> None:  # pragma: win32 no cover
+    helpers.assert_version_default('docker', version)
+    helpers.assert_no_additional_deps('docker', additional_dependencies)
+    assert_docker_available()
+
+    directory = prefix.path(
+        helpers.environment_dir(ENVIRONMENT_DIR, C.DEFAULT),
+    )
+
+    # Docker doesn't really have relevant disk environment, but pre-commit
+    # still needs to cleanup its state files on failure
+    with clean_path_on_failure(directory):
+        build_docker_image(prefix, pull=True)
+        os.mkdir(directory)
+
+
+def get_docker_user() -> str:  # pragma: win32 no cover
+    try:
+        return f'{os.getuid()}:{os.getgid()}'
+    except AttributeError:
+        return '1000:1000'
+
+
+def docker_cmd() -> Tuple[str, ...]:  # pragma: win32 no cover
+    return (
+        'docker', 'run',
+        '--rm',
+        '-u', get_docker_user(),
+        # https://docs.docker.com/engine/reference/commandline/run/#mount-volumes-from-container-volumes-from
+        # The `Z` option tells Docker to label the content with a private
+        # unshared label. Only the current container can use a private volume.
+        '-v', f'{os.getcwd()}:/src:rw,Z',
+        '--workdir', '/src',
+    )
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:  # pragma: win32 no cover
+    assert_docker_available()
+    # Rebuild the docker image in case it has gone missing, as many people do
+    # automated cleanup of docker images.
+    build_docker_image(hook.prefix, pull=False)
+
+    hook_cmd = hook.cmd
+    entry_exe, cmd_rest = hook.cmd[0], hook_cmd[1:]
+
+    entry_tag = ('--entrypoint', entry_exe, docker_tag(hook.prefix))
+    cmd = docker_cmd() + entry_tag + cmd_rest
+    return helpers.run_xargs(hook, cmd, file_args, color=color)
diff --git a/pre_commit/languages/docker_image.py b/pre_commit/languages/docker_image.py
new file mode 100644
index 0000000..0c51df6
--- /dev/null
+++ b/pre_commit/languages/docker_image.py
@@ -0,0 +1,22 @@
+from typing import Sequence
+from typing import Tuple
+
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+from pre_commit.languages.docker import assert_docker_available
+from pre_commit.languages.docker import docker_cmd
+
+ENVIRONMENT_DIR = None
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+install_environment = helpers.no_install
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:  # pragma: win32 no cover
+    assert_docker_available()
+    cmd = docker_cmd() + hook.cmd
+    return helpers.run_xargs(hook, cmd, file_args, color=color)
diff --git a/pre_commit/languages/fail.py b/pre_commit/languages/fail.py
new file mode 100644
index 0000000..d2b02d2
--- /dev/null
+++ b/pre_commit/languages/fail.py
@@ -0,0 +1,20 @@
+from typing import Sequence
+from typing import Tuple
+
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+
+ENVIRONMENT_DIR = None
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+install_environment = helpers.no_install
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:
+    out = f'{hook.entry}\n\n'.encode()
+    out += b'\n'.join(f.encode() for f in file_args) + b'\n'
+    return 1, out
diff --git a/pre_commit/languages/golang.py b/pre_commit/languages/golang.py
new file mode 100644
index 0000000..91ade1e
--- /dev/null
+++ b/pre_commit/languages/golang.py
@@ -0,0 +1,97 @@
+import contextlib
+import os.path
+import sys
+from typing import Generator
+from typing import Sequence
+from typing import Tuple
+
+import pre_commit.constants as C
+from pre_commit import git
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import PatchesT
+from pre_commit.envcontext import Var
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+from pre_commit.prefix import Prefix
+from pre_commit.util import clean_path_on_failure
+from pre_commit.util import cmd_output
+from pre_commit.util import cmd_output_b
+from pre_commit.util import rmtree
+
+ENVIRONMENT_DIR = 'golangenv'
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+
+
+def get_env_patch(venv: str) -> PatchesT:
+    return (
+        ('PATH', (os.path.join(venv, 'bin'), os.pathsep, Var('PATH'))),
+    )
+
+
+@contextlib.contextmanager
+def in_env(prefix: Prefix) -> Generator[None, None, None]:
+    envdir = prefix.path(
+        helpers.environment_dir(ENVIRONMENT_DIR, C.DEFAULT),
+    )
+    with envcontext(get_env_patch(envdir)):
+        yield
+
+
+def guess_go_dir(remote_url: str) -> str:
+    if remote_url.endswith('.git'):
+        remote_url = remote_url[:-1 * len('.git')]
+    looks_like_url = (
+        not remote_url.startswith('file://') and
+        ('//' in remote_url or '@' in remote_url)
+    )
+    remote_url = remote_url.replace(':', '/')
+    if looks_like_url:
+        _, _, remote_url = remote_url.rpartition('//')
+        _, _, remote_url = remote_url.rpartition('@')
+        return remote_url
+    else:
+        return 'unknown_src_dir'
+
+
+def install_environment(
+        prefix: Prefix,
+        version: str,
+        additional_dependencies: Sequence[str],
+) -> None:
+    helpers.assert_version_default('golang', version)
+    directory = prefix.path(
+        helpers.environment_dir(ENVIRONMENT_DIR, C.DEFAULT),
+    )
+
+    with clean_path_on_failure(directory):
+        remote = git.get_remote_url(prefix.prefix_dir)
+        repo_src_dir = os.path.join(directory, 'src', guess_go_dir(remote))
+
+        # Clone into the goenv we'll create
+        helpers.run_setup_cmd(prefix, ('git', 'clone', '.', repo_src_dir))
+
+        if sys.platform == 'cygwin':  # pragma: no cover
+            _, gopath, _ = cmd_output('cygpath', '-w', directory)
+            gopath = gopath.strip()
+        else:
+            gopath = directory
+        env = dict(os.environ, GOPATH=gopath)
+        env.pop('GOBIN', None)
+        cmd_output_b('go', 'get', './...', cwd=repo_src_dir, env=env)
+        for dependency in additional_dependencies:
+            cmd_output_b('go', 'get', dependency, cwd=repo_src_dir, env=env)
+        # Same some disk space, we don't need these after installation
+        rmtree(prefix.path(directory, 'src'))
+        pkgdir = prefix.path(directory, 'pkg')
+        if os.path.exists(pkgdir):  # pragma: no cover (go<1.10)
+            rmtree(pkgdir)
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:
+    with in_env(hook.prefix):
+        return helpers.run_xargs(hook, hook.cmd, file_args, color=color)
diff --git a/pre_commit/languages/helpers.py b/pre_commit/languages/helpers.py
new file mode 100644
index 0000000..b5c95e5
--- /dev/null
+++ b/pre_commit/languages/helpers.py
@@ -0,0 +1,109 @@
+import multiprocessing
+import os
+import random
+from typing import Any
+from typing import List
+from typing import Optional
+from typing import overload
+from typing import Sequence
+from typing import Tuple
+from typing import TYPE_CHECKING
+
+import pre_commit.constants as C
+from pre_commit.hook import Hook
+from pre_commit.prefix import Prefix
+from pre_commit.util import cmd_output_b
+from pre_commit.xargs import xargs
+
+if TYPE_CHECKING:
+    from typing import NoReturn
+
+FIXED_RANDOM_SEED = 1542676186
+
+
+def run_setup_cmd(prefix: Prefix, cmd: Tuple[str, ...]) -> None:
+    cmd_output_b(*cmd, cwd=prefix.prefix_dir)
+
+
+@overload
+def environment_dir(d: None, language_version: str) -> None: ...
+@overload
+def environment_dir(d: str, language_version: str) -> str: ...
+
+
+def environment_dir(d: Optional[str], language_version: str) -> Optional[str]:
+    if d is None:
+        return None
+    else:
+        return f'{d}-{language_version}'
+
+
+def assert_version_default(binary: str, version: str) -> None:
+    if version != C.DEFAULT:
+        raise AssertionError(
+            f'For now, pre-commit requires system-installed {binary}',
+        )
+
+
+def assert_no_additional_deps(
+        lang: str,
+        additional_deps: Sequence[str],
+) -> None:
+    if additional_deps:
+        raise AssertionError(
+            f'For now, pre-commit does not support '
+            f'additional_dependencies for {lang}',
+        )
+
+
+def basic_get_default_version() -> str:
+    return C.DEFAULT
+
+
+def basic_healthy(prefix: Prefix, language_version: str) -> bool:
+    return True
+
+
+def no_install(
+        prefix: Prefix,
+        version: str,
+        additional_dependencies: Sequence[str],
+) -> 'NoReturn':
+    raise AssertionError('This type is not installable')
+
+
+def target_concurrency(hook: Hook) -> int:
+    if hook.require_serial or 'PRE_COMMIT_NO_CONCURRENCY' in os.environ:
+        return 1
+    else:
+        # Travis appears to have a bunch of CPUs, but we can't use them all.
+        if 'TRAVIS' in os.environ:
+            return 2
+        else:
+            try:
+                return multiprocessing.cpu_count()
+            except NotImplementedError:
+                return 1
+
+
+def _shuffled(seq: Sequence[str]) -> List[str]:
+    """Deterministically shuffle"""
+    fixed_random = random.Random()
+    fixed_random.seed(FIXED_RANDOM_SEED, version=1)
+
+    seq = list(seq)
+    random.shuffle(seq, random=fixed_random.random)
+    return seq
+
+
+def run_xargs(
+        hook: Hook,
+        cmd: Tuple[str, ...],
+        file_args: Sequence[str],
+        **kwargs: Any,
+) -> Tuple[int, bytes]:
+    # Shuffle the files so that they more evenly fill out the xargs partitions,
+    # but do it deterministically in case a hook cares about ordering.
+    file_args = _shuffled(file_args)
+    kwargs['target_concurrency'] = target_concurrency(hook)
+    return xargs(cmd, file_args, **kwargs)
diff --git a/pre_commit/languages/node.py b/pre_commit/languages/node.py
new file mode 100644
index 0000000..79ff807
--- /dev/null
+++ b/pre_commit/languages/node.py
@@ -0,0 +1,93 @@
+import contextlib
+import os
+import sys
+from typing import Generator
+from typing import Sequence
+from typing import Tuple
+
+import pre_commit.constants as C
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import PatchesT
+from pre_commit.envcontext import Var
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+from pre_commit.languages.python import bin_dir
+from pre_commit.prefix import Prefix
+from pre_commit.util import clean_path_on_failure
+from pre_commit.util import cmd_output
+from pre_commit.util import cmd_output_b
+
+ENVIRONMENT_DIR = 'node_env'
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+
+
+def _envdir(prefix: Prefix, version: str) -> str:
+    directory = helpers.environment_dir(ENVIRONMENT_DIR, version)
+    return prefix.path(directory)
+
+
+def get_env_patch(venv: str) -> PatchesT:
+    if sys.platform == 'cygwin':  # pragma: no cover
+        _, win_venv, _ = cmd_output('cygpath', '-w', venv)
+        install_prefix = fr'{win_venv.strip()}\bin'
+        lib_dir = 'lib'
+    elif sys.platform == 'win32':  # pragma: no cover
+        install_prefix = bin_dir(venv)
+        lib_dir = 'Scripts'
+    else:  # pragma: win32 no cover
+        install_prefix = venv
+        lib_dir = 'lib'
+    return (
+        ('NODE_VIRTUAL_ENV', venv),
+        ('NPM_CONFIG_PREFIX', install_prefix),
+        ('npm_config_prefix', install_prefix),
+        ('NODE_PATH', os.path.join(venv, lib_dir, 'node_modules')),
+        ('PATH', (bin_dir(venv), os.pathsep, Var('PATH'))),
+    )
+
+
+@contextlib.contextmanager
+def in_env(
+        prefix: Prefix,
+        language_version: str,
+) -> Generator[None, None, None]:
+    with envcontext(get_env_patch(_envdir(prefix, language_version))):
+        yield
+
+
+def install_environment(
+        prefix: Prefix, version: str, additional_dependencies: Sequence[str],
+) -> None:
+    additional_dependencies = tuple(additional_dependencies)
+    assert prefix.exists('package.json')
+    envdir = _envdir(prefix, version)
+
+    # https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx?f=255&MSPPError=-2147217396#maxpath
+    if sys.platform == 'win32':  # pragma: no cover
+        envdir = f'\\\\?\\{os.path.normpath(envdir)}'
+    with clean_path_on_failure(envdir):
+        cmd = [
+            sys.executable, '-mnodeenv', '--prebuilt', '--clean-src', envdir,
+        ]
+        if version != C.DEFAULT:
+            cmd.extend(['-n', version])
+        cmd_output_b(*cmd)
+
+        with in_env(prefix, version):
+            # https://npm.community/t/npm-install-g-git-vs-git-clone-cd-npm-install-g/5449
+            # install as if we installed from git
+            helpers.run_setup_cmd(prefix, ('npm', 'install'))
+            helpers.run_setup_cmd(
+                prefix,
+                ('npm', 'install', '-g', '.', *additional_dependencies),
+            )
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:
+    with in_env(hook.prefix, hook.language_version):
+        return helpers.run_xargs(hook, hook.cmd, file_args, color=color)
diff --git a/pre_commit/languages/perl.py b/pre_commit/languages/perl.py
new file mode 100644
index 0000000..bbf5504
--- /dev/null
+++ b/pre_commit/languages/perl.py
@@ -0,0 +1,67 @@
+import contextlib
+import os
+import shlex
+from typing import Generator
+from typing import Sequence
+from typing import Tuple
+
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import PatchesT
+from pre_commit.envcontext import Var
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+from pre_commit.prefix import Prefix
+from pre_commit.util import clean_path_on_failure
+
+ENVIRONMENT_DIR = 'perl_env'
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+
+
+def _envdir(prefix: Prefix, version: str) -> str:
+    directory = helpers.environment_dir(ENVIRONMENT_DIR, version)
+    return prefix.path(directory)
+
+
+def get_env_patch(venv: str) -> PatchesT:
+    return (
+        ('PATH', (os.path.join(venv, 'bin'), os.pathsep, Var('PATH'))),
+        ('PERL5LIB', os.path.join(venv, 'lib', 'perl5')),
+        ('PERL_MB_OPT', f'--install_base {shlex.quote(venv)}'),
+        (
+            'PERL_MM_OPT', (
+                f'INSTALL_BASE={shlex.quote(venv)} '
+                f'INSTALLSITEMAN1DIR=none INSTALLSITEMAN3DIR=none'
+            ),
+        ),
+    )
+
+
+@contextlib.contextmanager
+def in_env(
+        prefix: Prefix,
+        language_version: str,
+) -> Generator[None, None, None]:
+    with envcontext(get_env_patch(_envdir(prefix, language_version))):
+        yield
+
+
+def install_environment(
+        prefix: Prefix, version: str, additional_dependencies: Sequence[str],
+) -> None:
+    helpers.assert_version_default('perl', version)
+
+    with clean_path_on_failure(_envdir(prefix, version)):
+        with in_env(prefix, version):
+            helpers.run_setup_cmd(
+                prefix, ('cpan', '-T', '.', *additional_dependencies),
+            )
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:
+    with in_env(hook.prefix, hook.language_version):
+        return helpers.run_xargs(hook, hook.cmd, file_args, color=color)
diff --git a/pre_commit/languages/pygrep.py b/pre_commit/languages/pygrep.py
new file mode 100644
index 0000000..40adba0
--- /dev/null
+++ b/pre_commit/languages/pygrep.py
@@ -0,0 +1,87 @@
+import argparse
+import re
+import sys
+from typing import Optional
+from typing import Pattern
+from typing import Sequence
+from typing import Tuple
+
+from pre_commit import output
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+from pre_commit.xargs import xargs
+
+ENVIRONMENT_DIR = None
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+install_environment = helpers.no_install
+
+
+def _process_filename_by_line(pattern: Pattern[bytes], filename: str) -> int:
+    retv = 0
+    with open(filename, 'rb') as f:
+        for line_no, line in enumerate(f, start=1):
+            if pattern.search(line):
+                retv = 1
+                output.write(f'{filename}:{line_no}:')
+                output.write_line_b(line.rstrip(b'\r\n'))
+    return retv
+
+
+def _process_filename_at_once(pattern: Pattern[bytes], filename: str) -> int:
+    retv = 0
+    with open(filename, 'rb') as f:
+        contents = f.read()
+        match = pattern.search(contents)
+        if match:
+            retv = 1
+            line_no = contents[:match.start()].count(b'\n')
+            output.write(f'{filename}:{line_no + 1}:')
+
+            matched_lines = match[0].split(b'\n')
+            matched_lines[0] = contents.split(b'\n')[line_no]
+
+            output.write_line_b(b'\n'.join(matched_lines))
+    return retv
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:
+    exe = (sys.executable, '-m', __name__) + tuple(hook.args) + (hook.entry,)
+    return xargs(exe, file_args, color=color)
+
+
+def main(argv: Optional[Sequence[str]] = None) -> int:
+    parser = argparse.ArgumentParser(
+        description=(
+            'grep-like finder using python regexes.  Unlike grep, this tool '
+            'returns nonzero when it finds a match and zero otherwise.  The '
+            'idea here being that matches are "problems".'
+        ),
+    )
+    parser.add_argument('-i', '--ignore-case', action='store_true')
+    parser.add_argument('--multiline', action='store_true')
+    parser.add_argument('pattern', help='python regex pattern.')
+    parser.add_argument('filenames', nargs='*')
+    args = parser.parse_args(argv)
+
+    flags = re.IGNORECASE if args.ignore_case else 0
+    if args.multiline:
+        flags |= re.MULTILINE | re.DOTALL
+
+    pattern = re.compile(args.pattern.encode(), flags)
+
+    retv = 0
+    for filename in args.filenames:
+        if args.multiline:
+            retv |= _process_filename_at_once(pattern, filename)
+        else:
+            retv |= _process_filename_by_line(pattern, filename)
+    return retv
+
+
+if __name__ == '__main__':
+    exit(main())
diff --git a/pre_commit/languages/python.py b/pre_commit/languages/python.py
new file mode 100644
index 0000000..5073a8b
--- /dev/null
+++ b/pre_commit/languages/python.py
@@ -0,0 +1,210 @@
+import contextlib
+import functools
+import os
+import sys
+from typing import Callable
+from typing import ContextManager
+from typing import Generator
+from typing import Optional
+from typing import Sequence
+from typing import Tuple
+
+import pre_commit.constants as C
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import PatchesT
+from pre_commit.envcontext import UNSET
+from pre_commit.envcontext import Var
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+from pre_commit.parse_shebang import find_executable
+from pre_commit.prefix import Prefix
+from pre_commit.util import CalledProcessError
+from pre_commit.util import clean_path_on_failure
+from pre_commit.util import cmd_output
+from pre_commit.util import cmd_output_b
+
+ENVIRONMENT_DIR = 'py_env'
+
+
+def bin_dir(venv: str) -> str:
+    """On windows there's a different directory for the virtualenv"""
+    bin_part = 'Scripts' if os.name == 'nt' else 'bin'
+    return os.path.join(venv, bin_part)
+
+
+def get_env_patch(venv: str) -> PatchesT:
+    return (
+        ('PYTHONHOME', UNSET),
+        ('VIRTUAL_ENV', venv),
+        ('PATH', (bin_dir(venv), os.pathsep, Var('PATH'))),
+    )
+
+
+def _find_by_py_launcher(
+        version: str,
+) -> Optional[str]:  # pragma: no cover (windows only)
+    if version.startswith('python'):
+        num = version[len('python'):]
+        try:
+            cmd = ('py', f'-{num}', '-c', 'import sys; print(sys.executable)')
+            return cmd_output(*cmd)[1].strip()
+        except CalledProcessError:
+            pass
+    return None
+
+
+def _find_by_sys_executable() -> Optional[str]:
+    def _norm(path: str) -> Optional[str]:
+        _, exe = os.path.split(path.lower())
+        exe, _, _ = exe.partition('.exe')
+        if exe not in {'python', 'pythonw'} and find_executable(exe):
+            return exe
+        return None
+
+    # On linux, I see these common sys.executables:
+    #
+    # system `python`: /usr/bin/python -> python2.7
+    # system `python2`: /usr/bin/python2 -> python2.7
+    # virtualenv v: v/bin/python (will not return from this loop)
+    # virtualenv v -ppython2: v/bin/python -> python2
+    # virtualenv v -ppython2.7: v/bin/python -> python2.7
+    # virtualenv v -ppypy: v/bin/python -> v/bin/pypy
+    for path in (sys.executable, os.path.realpath(sys.executable)):
+        exe = _norm(path)
+        if exe:
+            return exe
+    return None
+
+
+@functools.lru_cache(maxsize=1)
+def get_default_version() -> str:  # pragma: no cover (platform dependent)
+    # First attempt from `sys.executable` (or the realpath)
+    exe = _find_by_sys_executable()
+    if exe:
+        return exe
+
+    # Next try the `pythonX.X` executable
+    exe = f'python{sys.version_info[0]}.{sys.version_info[1]}'
+    if find_executable(exe):
+        return exe
+
+    if _find_by_py_launcher(exe):
+        return exe
+
+    # Give a best-effort try for windows
+    default_folder_name = exe.replace('.', '')
+    if os.path.exists(fr'C:\{default_folder_name}\python.exe'):
+        return exe
+
+    # We tried!
+    return C.DEFAULT
+
+
+def _sys_executable_matches(version: str) -> bool:
+    if version == 'python':
+        return True
+    elif not version.startswith('python'):
+        return False
+
+    try:
+        info = tuple(int(p) for p in version[len('python'):].split('.'))
+    except ValueError:
+        return False
+
+    return sys.version_info[:len(info)] == info
+
+
+def norm_version(version: str) -> str:
+    # first see if our current executable is appropriate
+    if _sys_executable_matches(version):
+        return sys.executable
+
+    if os.name == 'nt':  # pragma: no cover (windows)
+        version_exec = _find_by_py_launcher(version)
+        if version_exec:
+            return version_exec
+
+        # Try looking up by name
+        version_exec = find_executable(version)
+        if version_exec and version_exec != version:
+            return version_exec
+
+        # If it is in the form pythonx.x search in the default
+        # place on windows
+        if version.startswith('python'):
+            default_folder_name = version.replace('.', '')
+            return fr'C:\{default_folder_name}\python.exe'
+
+    # Otherwise assume it is a path
+    return os.path.expanduser(version)
+
+
+def py_interface(
+        _dir: str,
+        _make_venv: Callable[[str, str], None],
+) -> Tuple[
+    Callable[[Prefix, str], ContextManager[None]],
+    Callable[[Prefix, str], bool],
+    Callable[[Hook, Sequence[str], bool], Tuple[int, bytes]],
+    Callable[[Prefix, str, Sequence[str]], None],
+]:
+    @contextlib.contextmanager
+    def in_env(
+            prefix: Prefix,
+            language_version: str,
+    ) -> Generator[None, None, None]:
+        envdir = prefix.path(helpers.environment_dir(_dir, language_version))
+        with envcontext(get_env_patch(envdir)):
+            yield
+
+    def healthy(prefix: Prefix, language_version: str) -> bool:
+        envdir = helpers.environment_dir(_dir, language_version)
+        exe_name = 'python.exe' if sys.platform == 'win32' else 'python'
+        py_exe = prefix.path(bin_dir(envdir), exe_name)
+        with in_env(prefix, language_version):
+            retcode, _, _ = cmd_output_b(
+                py_exe, '-c', 'import ctypes, datetime, io, os, ssl, weakref',
+                cwd='/',
+                retcode=None,
+            )
+        return retcode == 0
+
+    def run_hook(
+            hook: Hook,
+            file_args: Sequence[str],
+            color: bool,
+    ) -> Tuple[int, bytes]:
+        with in_env(hook.prefix, hook.language_version):
+            return helpers.run_xargs(hook, hook.cmd, file_args, color=color)
+
+    def install_environment(
+            prefix: Prefix,
+            version: str,
+            additional_dependencies: Sequence[str],
+    ) -> None:
+        additional_dependencies = tuple(additional_dependencies)
+        directory = helpers.environment_dir(_dir, version)
+
+        env_dir = prefix.path(directory)
+        with clean_path_on_failure(env_dir):
+            if version != C.DEFAULT:
+                python = norm_version(version)
+            else:
+                python = os.path.realpath(sys.executable)
+            _make_venv(env_dir, python)
+            with in_env(prefix, version):
+                helpers.run_setup_cmd(
+                    prefix, ('pip', 'install', '.') + additional_dependencies,
+                )
+
+    return in_env, healthy, run_hook, install_environment
+
+
+def make_venv(envdir: str, python: str) -> None:
+    env = dict(os.environ, VIRTUALENV_NO_DOWNLOAD='1')
+    cmd = (sys.executable, '-mvirtualenv', envdir, '-p', python)
+    cmd_output_b(*cmd, env=env, cwd='/')
+
+
+_interface = py_interface(ENVIRONMENT_DIR, make_venv)
+in_env, healthy, run_hook, install_environment = _interface
diff --git a/pre_commit/languages/python_venv.py b/pre_commit/languages/python_venv.py
new file mode 100644
index 0000000..5404c8b
--- /dev/null
+++ b/pre_commit/languages/python_venv.py
@@ -0,0 +1,46 @@
+import os.path
+
+from pre_commit.languages import python
+from pre_commit.util import CalledProcessError
+from pre_commit.util import cmd_output
+from pre_commit.util import cmd_output_b
+
+ENVIRONMENT_DIR = 'py_venv'
+get_default_version = python.get_default_version
+
+
+def orig_py_exe(exe: str) -> str:  # pragma: no cover (platform specific)
+    """A -mvenv virtualenv made from a -mvirtualenv virtualenv installs
+    packages to the incorrect location.  Attempt to find the _original_ exe
+    and invoke `-mvenv` from there.
+
+    See:
+    - https://github.com/pre-commit/pre-commit/issues/755
+    - https://github.com/pypa/virtualenv/issues/1095
+    - https://bugs.python.org/issue30811
+    """
+    try:
+        prefix_script = 'import sys; print(sys.real_prefix)'
+        _, prefix, _ = cmd_output(exe, '-c', prefix_script)
+        prefix = prefix.strip()
+    except CalledProcessError:
+        # not created from -mvirtualenv
+        return exe
+
+    if os.name == 'nt':
+        expected = os.path.join(prefix, 'python.exe')
+    else:
+        expected = os.path.join(prefix, 'bin', os.path.basename(exe))
+
+    if os.path.exists(expected):
+        return expected
+    else:
+        return exe
+
+
+def make_venv(envdir: str, python: str) -> None:
+    cmd_output_b(orig_py_exe(python), '-mvenv', envdir, cwd='/')
+
+
+_interface = python.py_interface(ENVIRONMENT_DIR, make_venv)
+in_env, healthy, run_hook, install_environment = _interface
diff --git a/pre_commit/languages/ruby.py b/pre_commit/languages/ruby.py
new file mode 100644
index 0000000..61241f8
--- /dev/null
+++ b/pre_commit/languages/ruby.py
@@ -0,0 +1,126 @@
+import contextlib
+import os.path
+import shutil
+import tarfile
+from typing import Generator
+from typing import Sequence
+from typing import Tuple
+
+import pre_commit.constants as C
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import PatchesT
+from pre_commit.envcontext import Var
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+from pre_commit.prefix import Prefix
+from pre_commit.util import CalledProcessError
+from pre_commit.util import clean_path_on_failure
+from pre_commit.util import resource_bytesio
+
+ENVIRONMENT_DIR = 'rbenv'
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+
+
+def get_env_patch(
+        venv: str,
+        language_version: str,
+) -> PatchesT:  # pragma: win32 no cover
+    patches: PatchesT = (
+        ('GEM_HOME', os.path.join(venv, 'gems')),
+        ('RBENV_ROOT', venv),
+        ('BUNDLE_IGNORE_CONFIG', '1'),
+        (
+            'PATH', (
+                os.path.join(venv, 'gems', 'bin'), os.pathsep,
+                os.path.join(venv, 'shims'), os.pathsep,
+                os.path.join(venv, 'bin'), os.pathsep, Var('PATH'),
+            ),
+        ),
+    )
+    if language_version != C.DEFAULT:
+        patches += (('RBENV_VERSION', language_version),)
+    return patches
+
+
+@contextlib.contextmanager  # pragma: win32 no cover
+def in_env(
+        prefix: Prefix,
+        language_version: str,
+) -> Generator[None, None, None]:
+    envdir = prefix.path(
+        helpers.environment_dir(ENVIRONMENT_DIR, language_version),
+    )
+    with envcontext(get_env_patch(envdir, language_version)):
+        yield
+
+
+def _extract_resource(filename: str, dest: str) -> None:
+    with resource_bytesio(filename) as bio:
+        with tarfile.open(fileobj=bio) as tf:
+            tf.extractall(dest)
+
+
+def _install_rbenv(
+        prefix: Prefix,
+        version: str = C.DEFAULT,
+) -> None:  # pragma: win32 no cover
+    directory = helpers.environment_dir(ENVIRONMENT_DIR, version)
+
+    _extract_resource('rbenv.tar.gz', prefix.path('.'))
+    shutil.move(prefix.path('rbenv'), prefix.path(directory))
+
+    # Only install ruby-build if the version is specified
+    if version != C.DEFAULT:
+        plugins_dir = prefix.path(directory, 'plugins')
+        _extract_resource('ruby-download.tar.gz', plugins_dir)
+        _extract_resource('ruby-build.tar.gz', plugins_dir)
+
+
+def _install_ruby(
+        prefix: Prefix,
+        version: str,
+) -> None:  # pragma: win32 no cover
+    try:
+        helpers.run_setup_cmd(prefix, ('rbenv', 'download', version))
+    except CalledProcessError:  # pragma: no cover (usually find with download)
+        # Failed to download from mirror for some reason, build it instead
+        helpers.run_setup_cmd(prefix, ('rbenv', 'install', version))
+
+
+def install_environment(
+        prefix: Prefix, version: str, additional_dependencies: Sequence[str],
+) -> None:  # pragma: win32 no cover
+    additional_dependencies = tuple(additional_dependencies)
+    directory = helpers.environment_dir(ENVIRONMENT_DIR, version)
+    with clean_path_on_failure(prefix.path(directory)):
+        # TODO: this currently will fail if there's no version specified and
+        # there's no system ruby installed.  Is this ok?
+        _install_rbenv(prefix, version=version)
+        with in_env(prefix, version):
+            # Need to call this before installing so rbenv's directories are
+            # set up
+            helpers.run_setup_cmd(prefix, ('rbenv', 'init', '-'))
+            if version != C.DEFAULT:
+                _install_ruby(prefix, version)
+            # Need to call this after installing to set up the shims
+            helpers.run_setup_cmd(prefix, ('rbenv', 'rehash'))
+            helpers.run_setup_cmd(
+                prefix, ('gem', 'build', *prefix.star('.gemspec')),
+            )
+            helpers.run_setup_cmd(
+                prefix,
+                (
+                    'gem', 'install', '--no-document',
+                    *prefix.star('.gem'), *additional_dependencies,
+                ),
+            )
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:  # pragma: win32 no cover
+    with in_env(hook.prefix, hook.language_version):
+        return helpers.run_xargs(hook, hook.cmd, file_args, color=color)
diff --git a/pre_commit/languages/rust.py b/pre_commit/languages/rust.py
new file mode 100644
index 0000000..7ea3f54
--- /dev/null
+++ b/pre_commit/languages/rust.py
@@ -0,0 +1,106 @@
+import contextlib
+import os.path
+from typing import Generator
+from typing import Sequence
+from typing import Set
+from typing import Tuple
+
+import toml
+
+import pre_commit.constants as C
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import PatchesT
+from pre_commit.envcontext import Var
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+from pre_commit.prefix import Prefix
+from pre_commit.util import clean_path_on_failure
+from pre_commit.util import cmd_output_b
+
+ENVIRONMENT_DIR = 'rustenv'
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+
+
+def get_env_patch(target_dir: str) -> PatchesT:
+    return (
+        ('PATH', (os.path.join(target_dir, 'bin'), os.pathsep, Var('PATH'))),
+    )
+
+
+@contextlib.contextmanager
+def in_env(prefix: Prefix) -> Generator[None, None, None]:
+    target_dir = prefix.path(
+        helpers.environment_dir(ENVIRONMENT_DIR, C.DEFAULT),
+    )
+    with envcontext(get_env_patch(target_dir)):
+        yield
+
+
+def _add_dependencies(
+        cargo_toml_path: str,
+        additional_dependencies: Set[str],
+) -> None:
+    with open(cargo_toml_path, 'r+') as f:
+        cargo_toml = toml.load(f)
+        cargo_toml.setdefault('dependencies', {})
+        for dep in additional_dependencies:
+            name, _, spec = dep.partition(':')
+            cargo_toml['dependencies'][name] = spec or '*'
+        f.seek(0)
+        toml.dump(cargo_toml, f)
+        f.truncate()
+
+
+def install_environment(
+        prefix: Prefix,
+        version: str,
+        additional_dependencies: Sequence[str],
+) -> None:
+    helpers.assert_version_default('rust', version)
+    directory = prefix.path(
+        helpers.environment_dir(ENVIRONMENT_DIR, C.DEFAULT),
+    )
+
+    # There are two cases where we might want to specify more dependencies:
+    # as dependencies for the library being built, and as binary packages
+    # to be `cargo install`'d.
+    #
+    # Unlike e.g. Python, if we just `cargo install` a library, it won't be
+    # used for compilation. And if we add a crate providing a binary to the
+    # `Cargo.toml`, the binary won't be built.
+    #
+    # Because of this, we allow specifying "cli" dependencies by prefixing
+    # with 'cli:'.
+    cli_deps = {
+        dep for dep in additional_dependencies if dep.startswith('cli:')
+    }
+    lib_deps = set(additional_dependencies) - cli_deps
+
+    if len(lib_deps) > 0:
+        _add_dependencies(prefix.path('Cargo.toml'), lib_deps)
+
+    with clean_path_on_failure(directory):
+        packages_to_install: Set[Tuple[str, ...]] = {('--path', '.')}
+        for cli_dep in cli_deps:
+            cli_dep = cli_dep[len('cli:'):]
+            package, _, version = cli_dep.partition(':')
+            if version != '':
+                packages_to_install.add((package, '--version', version))
+            else:
+                packages_to_install.add((package,))
+
+        for args in packages_to_install:
+            cmd_output_b(
+                'cargo', 'install', '--bins', '--root', directory, *args,
+                cwd=prefix.prefix_dir,
+            )
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:
+    with in_env(hook.prefix):
+        return helpers.run_xargs(hook, hook.cmd, file_args, color=color)
diff --git a/pre_commit/languages/script.py b/pre_commit/languages/script.py
new file mode 100644
index 0000000..a5e1365
--- /dev/null
+++ b/pre_commit/languages/script.py
@@ -0,0 +1,19 @@
+from typing import Sequence
+from typing import Tuple
+
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+
+ENVIRONMENT_DIR = None
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+install_environment = helpers.no_install
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:
+    cmd = (hook.prefix.path(hook.cmd[0]), *hook.cmd[1:])
+    return helpers.run_xargs(hook, cmd, file_args, color=color)
diff --git a/pre_commit/languages/swift.py b/pre_commit/languages/swift.py
new file mode 100644
index 0000000..66aadc8
--- /dev/null
+++ b/pre_commit/languages/swift.py
@@ -0,0 +1,64 @@
+import contextlib
+import os
+from typing import Generator
+from typing import Sequence
+from typing import Tuple
+
+import pre_commit.constants as C
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import PatchesT
+from pre_commit.envcontext import Var
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+from pre_commit.prefix import Prefix
+from pre_commit.util import clean_path_on_failure
+from pre_commit.util import cmd_output_b
+
+ENVIRONMENT_DIR = 'swift_env'
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+BUILD_DIR = '.build'
+BUILD_CONFIG = 'release'
+
+
+def get_env_patch(venv: str) -> PatchesT:  # pragma: win32 no cover
+    bin_path = os.path.join(venv, BUILD_DIR, BUILD_CONFIG)
+    return (('PATH', (bin_path, os.pathsep, Var('PATH'))),)
+
+
+@contextlib.contextmanager  # pragma: win32 no cover
+def in_env(prefix: Prefix) -> Generator[None, None, None]:
+    envdir = prefix.path(
+        helpers.environment_dir(ENVIRONMENT_DIR, C.DEFAULT),
+    )
+    with envcontext(get_env_patch(envdir)):
+        yield
+
+
+def install_environment(
+        prefix: Prefix, version: str, additional_dependencies: Sequence[str],
+) -> None:  # pragma: win32 no cover
+    helpers.assert_version_default('swift', version)
+    helpers.assert_no_additional_deps('swift', additional_dependencies)
+    directory = prefix.path(
+        helpers.environment_dir(ENVIRONMENT_DIR, C.DEFAULT),
+    )
+
+    # Build the swift package
+    with clean_path_on_failure(directory):
+        os.mkdir(directory)
+        cmd_output_b(
+            'swift', 'build',
+            '-C', prefix.prefix_dir,
+            '-c', BUILD_CONFIG,
+            '--build-path', os.path.join(directory, BUILD_DIR),
+        )
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:  # pragma: win32 no cover
+    with in_env(hook.prefix):
+        return helpers.run_xargs(hook, hook.cmd, file_args, color=color)
diff --git a/pre_commit/languages/system.py b/pre_commit/languages/system.py
new file mode 100644
index 0000000..139f45d
--- /dev/null
+++ b/pre_commit/languages/system.py
@@ -0,0 +1,19 @@
+from typing import Sequence
+from typing import Tuple
+
+from pre_commit.hook import Hook
+from pre_commit.languages import helpers
+
+
+ENVIRONMENT_DIR = None
+get_default_version = helpers.basic_get_default_version
+healthy = helpers.basic_healthy
+install_environment = helpers.no_install
+
+
+def run_hook(
+        hook: Hook,
+        file_args: Sequence[str],
+        color: bool,
+) -> Tuple[int, bytes]:
+    return helpers.run_xargs(hook, hook.cmd, file_args, color=color)