1 files changed, 157 insertions, 0 deletions
diff --git a/pre_commit/xargs.py b/pre_commit/xargs.py
new file mode 100644
index 0000000..5235dc6
--- /dev/null
+++ b/pre_commit/xargs.py
@@ -0,0 +1,157 @@
+import concurrent.futures
+import contextlib
+import math
+import os
+import subprocess
+import sys
+from typing import Any
+from typing import Callable
+from typing import Generator
+from typing import Iterable
+from typing import List
+from typing import Optional
+from typing import Sequence
+from typing import Tuple
+from typing import TypeVar
+
+from pre_commit import parse_shebang
+from pre_commit.util import cmd_output_b
+from pre_commit.util import cmd_output_p
+from pre_commit.util import EnvironT
+
+TArg = TypeVar('TArg')
+TRet = TypeVar('TRet')
+
+
+def _environ_size(_env: Optional[EnvironT] = None) -> int:
+    environ = _env if _env is not None else getattr(os, 'environb', os.environ)
+    size = 8 * len(environ)  # number of pointers in `envp`
+    for k, v in environ.items():
+        size += len(k) + len(v) + 2  # c strings in `envp`
+    return size
+
+
+def _get_platform_max_length() -> int:  # pragma: no cover (platform specific)
+    if os.name == 'posix':
+        maximum = os.sysconf('SC_ARG_MAX') - 2048 - _environ_size()
+        maximum = max(min(maximum, 2 ** 17), 2 ** 12)
+        return maximum
+    elif os.name == 'nt':
+        return 2 ** 15 - 2048  # UNICODE_STRING max - headroom
+    else:
+        # posix minimum
+        return 2 ** 12
+
+
+def _command_length(*cmd: str) -> int:
+    full_cmd = ' '.join(cmd)
+
+    # win32 uses the amount of characters, more details at:
+    # https://github.com/pre-commit/pre-commit/pull/839
+    if sys.platform == 'win32':
+        return len(full_cmd.encode('utf-16le')) // 2
+    else:
+        return len(full_cmd.encode(sys.getfilesystemencoding()))
+
+
+class ArgumentTooLongError(RuntimeError):
+    pass
+
+
+def partition(
+        cmd: Sequence[str],
+        varargs: Sequence[str],
+        target_concurrency: int,
+        _max_length: Optional[int] = None,
+) -> Tuple[Tuple[str, ...], ...]:
+    _max_length = _max_length or _get_platform_max_length()
+
+    # Generally, we try to partition evenly into at least `target_concurrency`
+    # partitions, but we don't want a bunch of tiny partitions.
+    max_args = max(4, math.ceil(len(varargs) / target_concurrency))
+
+    cmd = tuple(cmd)
+    ret = []
+
+    ret_cmd: List[str] = []
+    # Reversed so arguments are in order
+    varargs = list(reversed(varargs))
+
+    total_length = _command_length(*cmd) + 1
+    while varargs:
+        arg = varargs.pop()
+
+        arg_length = _command_length(arg) + 1
+        if (
+                total_length + arg_length <= _max_length and
+                len(ret_cmd) < max_args
+        ):
+            ret_cmd.append(arg)
+            total_length += arg_length
+        elif not ret_cmd:
+            raise ArgumentTooLongError(arg)
+        else:
+            # We've exceeded the length, yield a command
+            ret.append(cmd + tuple(ret_cmd))
+            ret_cmd = []
+            total_length = _command_length(*cmd) + 1
+            varargs.append(arg)
+
+    ret.append(cmd + tuple(ret_cmd))
+
+    return tuple(ret)
+
+
+@contextlib.contextmanager
+def _thread_mapper(maxsize: int) -> Generator[
+    Callable[[Callable[[TArg], TRet], Iterable[TArg]], Iterable[TRet]],
+    None, None,
+]:
+    if maxsize == 1:
+        yield map
+    else:
+        with concurrent.futures.ThreadPoolExecutor(maxsize) as ex:
+            yield ex.map
+
+
+def xargs(
+        cmd: Tuple[str, ...],
+        varargs: Sequence[str],
+        *,
+        color: bool = False,
+        target_concurrency: int = 1,
+        _max_length: int = _get_platform_max_length(),
+        **kwargs: Any,
+) -> Tuple[int, bytes]:
+    """A simplified implementation of xargs.
+
+    color: Make a pty if on a platform that supports it
+    target_concurrency: Target number of partitions to run concurrently
+    """
+    cmd_fn = cmd_output_p if color else cmd_output_b
+    retcode = 0
+    stdout = b''
+
+    try:
+        cmd = parse_shebang.normalize_cmd(cmd)
+    except parse_shebang.ExecutableNotFoundError as e:
+        return e.to_output()[:2]
+
+    partitions = partition(cmd, varargs, target_concurrency, _max_length)
+
+    def run_cmd_partition(
+            run_cmd: Tuple[str, ...],
+    ) -> Tuple[int, bytes, Optional[bytes]]:
+        return cmd_fn(
+            *run_cmd, retcode=None, stderr=subprocess.STDOUT, **kwargs,
+        )
+
+    threads = min(len(partitions), target_concurrency)
+    with _thread_mapper(threads) as thread_map:
+        results = thread_map(run_cmd_partition, partitions)
+
+        for proc_retcode, proc_out, _ in results:
+            retcode = max(retcode, proc_retcode)
+            stdout += proc_out
+
+    return retcode, stdout