1 files changed, 84 insertions, 0 deletions
diff --git a/pre_commit/parse_shebang.py b/pre_commit/parse_shebang.py
new file mode 100644
index 0000000..d344a1d
--- /dev/null
+++ b/pre_commit/parse_shebang.py
@@ -0,0 +1,84 @@
+import os.path
+from typing import Mapping
+from typing import Optional
+from typing import Tuple
+from typing import TYPE_CHECKING
+
+from identify.identify import parse_shebang_from_file
+
+if TYPE_CHECKING:
+    from typing import NoReturn
+
+
+class ExecutableNotFoundError(OSError):
+    def to_output(self) -> Tuple[int, bytes, None]:
+        return (1, self.args[0].encode(), None)
+
+
+def parse_filename(filename: str) -> Tuple[str, ...]:
+    if not os.path.exists(filename):
+        return ()
+    else:
+        return parse_shebang_from_file(filename)
+
+
+def find_executable(
+        exe: str, _environ: Optional[Mapping[str, str]] = None,
+) -> Optional[str]:
+    exe = os.path.normpath(exe)
+    if os.sep in exe:
+        return exe
+
+    environ = _environ if _environ is not None else os.environ
+
+    if 'PATHEXT' in environ:
+        exts = environ['PATHEXT'].split(os.pathsep)
+        possible_exe_names = tuple(f'{exe}{ext}' for ext in exts) + (exe,)
+    else:
+        possible_exe_names = (exe,)
+
+    for path in environ.get('PATH', '').split(os.pathsep):
+        for possible_exe_name in possible_exe_names:
+            joined = os.path.join(path, possible_exe_name)
+            if os.path.isfile(joined) and os.access(joined, os.X_OK):
+                return joined
+    else:
+        return None
+
+
+def normexe(orig: str) -> str:
+    def _error(msg: str) -> 'NoReturn':
+        raise ExecutableNotFoundError(f'Executable `{orig}` {msg}')
+
+    if os.sep not in orig and (not os.altsep or os.altsep not in orig):
+        exe = find_executable(orig)
+        if exe is None:
+            _error('not found')
+        return exe
+    elif os.path.isdir(orig):
+        _error('is a directory')
+    elif not os.path.isfile(orig):
+        _error('not found')
+    elif not os.access(orig, os.X_OK):  # pragma: win32 no cover
+        _error('is not executable')
+    else:
+        return orig
+
+
+def normalize_cmd(cmd: Tuple[str, ...]) -> Tuple[str, ...]:
+    """Fixes for the following issues on windows
+    - https://bugs.python.org/issue8557
+    - windows does not parse shebangs
+
+    This function also makes deep-path shebangs work just fine
+    """
+    # Use PATH to determine the executable
+    exe = normexe(cmd[0])
+
+    # Figure out the shebang from the resulting command
+    cmd = parse_filename(exe) + (exe,) + cmd[1:]
+
+    # This could have given us back another bare executable
+    exe = normexe(cmd[0])
+
+    return (exe,) + cmd[1:]