MAINT: Add functions to parse shell-strings in the platform-native way

There are places in distutils where we accept a single string from the user, and interpret it as a set of command line arguments.
Previously, these were passed on as a string unmodified to exec_command, and interpreted by subprocess in a platform-specific way.

Recent changes to distutils now pass a list of arguments to subprocess, meaning we have to split the strings ourselves.
While `shlex.split` is perfect on posix systems, it is not a good approximation of either the old or the expected behavior on windows.

Provides the building blocks needed to fix gh-12979

1 files changed, 91 insertions, 0 deletions

diff --git a/numpy/distutils/_shell_utils.py b/numpy/distutils/_shell_utils.py
new file mode 100644
index 000000000..5ef874900
--- /dev/null
+++ b/numpy/distutils/_shell_utils.py
@@ -0,0 +1,91 @@
+"""
+Helper functions for interacting with the shell, and consuming shell-style
+parameters provided in config files.
+"""
+import os
+import shlex
+import subprocess
+try:
+    from shlex import quote
+except ImportError:
+    from pipes import quote
+
+__all__ = ['WindowsParser', 'PosixParser', 'NativeParser']
+
+
+class CommandLineParser:
+    """
+    An object that knows how to split and join command-line arguments.
+
+    It must be true that ``argv == split(join(argv))`` for all ``argv``.
+    The reverse neednt be true - `join(split(cmd))` may result in the addition
+    or removal of unnecessary escaping.
+    """
+    @staticmethod
+    def join(argv):
+        """ Join a list of arguments into a command line string """
+        raise NotImplemented
+
+    @staticmethod
+    def split(cmd):
+        """ Split a command line string into a list of arguments """
+        raise NotImplemented
+
+
+class WindowsParser:
+    """
+    The parsing behavior used by `subprocess.call("string")` on Windows, which
+    matches the Microsoft C/C++ runtime.
+
+    Note that this is _not_ the behavior of cmd.
+    """
+    @staticmethod
+    def join(argv):
+        # note that list2cmdline is specific to the windows syntax
+        return subprocess.list2cmdline(argv)
+
+    @staticmethod
+    def split(cmd):
+        import ctypes  # guarded import for systems without ctypes
+        try:
+            ctypes.windll
+        except AttributeError:
+            raise NotImplementedError
+
+        # Windows has special parsing rules for the executable (no quotes),
+        # that we do not care about - insert a dummy element
+        if not cmd:
+            return []
+        cmd = 'dummy ' + cmd
+
+        CommandLineToArgvW = ctypes.windll.shell32.CommandLineToArgvW
+        CommandLineToArgvW.restype = ctypes.POINTER(ctypes.c_wchar_p)
+        CommandLineToArgvW.argtypes = (ctypes.c_wchar_p, ctypes.POINTER(ctypes.c_int))
+
+        nargs = ctypes.c_int()
+        lpargs = CommandLineToArgvW(cmd, ctypes.byref(nargs))
+        args = [lpargs[i] for i in range(nargs.value)]
+        assert not ctypes.windll.kernel32.LocalFree(lpargs)
+
+        # strip the element we inserted
+        assert args[0] == "dummy"
+        return args[1:]
+
+
+class PosixParser:
+    """
+    The parsing behavior used by `subprocess.call("string", shell=True)` on Posix.
+    """
+    @staticmethod
+    def join(argv):
+        return ' '.join(quote(arg) for arg in argv)
+
+    @staticmethod
+    def split(cmd):
+        return shlex.split(cmd, posix=True)
+
+
+if os.name == 'nt':
+    NativeParser = WindowsParser
+elif os.name == 'posix':
+    NativeParser = PosixParser