Vendor debugpy for VS Code attach debugging

Bundles debugpy 1.7.0 directly in python/ so "Maya: Attach (debugpy)"
works with no per-machine pip install step. Installed via Maya 2022's
own pip so it resolved a version actually compatible with Python 3.7
(Maya 2022's interpreter), then verified import + listen() succeeds
under all three target Maya Python versions (3.7/3.9/3.10).

Also fixes a latent __file__-under-exec() bug in
start_debug_server.py (same pitfall as Maya's own plugin loader,
never hit until this exercised it) and corrects the README's Maya
Python version claim -- 2022 ships Python 3.7, not 3.9 as previously
stated, which was never independently verified until now.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

python/debugpy/_vendored/__init__.py

@@ -0,0 +1,126 @@
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See LICENSE in the project root
+# for license information.
+
+import contextlib
+from importlib import import_module
+import os
+import sys
+
+from . import _util
+
+
+VENDORED_ROOT = os.path.dirname(os.path.abspath(__file__))
+# TODO: Move the "pydevd" git submodule to the debugpy/_vendored directory
+# and then drop the following fallback.
+if "pydevd" not in os.listdir(VENDORED_ROOT):
+    VENDORED_ROOT = os.path.dirname(VENDORED_ROOT)
+
+
+def list_all(resolve=False):
+    """Return the list of vendored projects."""
+    # TODO: Derive from os.listdir(VENDORED_ROOT)?
+    projects = ["pydevd"]
+    if not resolve:
+        return projects
+    return [project_root(name) for name in projects]
+
+
+def project_root(project):
+    """Return the path the root dir of the vendored project.
+
+    If "project" is an empty string then the path prefix for vendored
+    projects (e.g. "debugpy/_vendored/") will be returned.
+    """
+    if not project:
+        project = ""
+    return os.path.join(VENDORED_ROOT, project)
+
+
+def iter_project_files(project, relative=False, **kwargs):
+    """Yield (dirname, basename, filename) for all files in the project."""
+    if relative:
+        with _util.cwd(VENDORED_ROOT):
+            for result in _util.iter_all_files(project, **kwargs):
+                yield result
+    else:
+        root = project_root(project)
+        for result in _util.iter_all_files(root, **kwargs):
+            yield result
+
+
+def iter_packaging_files(project):
+    """Yield the filenames for all files in the project.
+
+    The filenames are relative to "debugpy/_vendored".  This is most
+    useful for the "package data" in a setup.py.
+    """
+    # TODO: Use default filters?  __pycache__ and .pyc?
+    prune_dir = None
+    exclude_file = None
+    try:
+        mod = import_module("._{}_packaging".format(project), __name__)
+    except ImportError:
+        pass
+    else:
+        prune_dir = getattr(mod, "prune_dir", prune_dir)
+        exclude_file = getattr(mod, "exclude_file", exclude_file)
+    results = iter_project_files(
+        project, relative=True, prune_dir=prune_dir, exclude_file=exclude_file
+    )
+    for _, _, filename in results:
+        yield filename
+
+
+def prefix_matcher(*prefixes):
+    """Return a module match func that matches any of the given prefixes."""
+    assert prefixes
+
+    def match(name, module):
+        for prefix in prefixes:
+            if name.startswith(prefix):
+                return True
+        else:
+            return False
+
+    return match
+
+
+def check_modules(project, match, root=None):
+    """Verify that only vendored modules have been imported."""
+    if root is None:
+        root = project_root(project)
+    extensions = []
+    unvendored = {}
+    for modname, mod in list(sys.modules.items()):
+        if not match(modname, mod):
+            continue
+        try:
+            filename = getattr(mod, "__file__", None)
+        except:  # In theory it's possible that any error is raised when accessing __file__
+            filename = None
+        if not filename:  # extension module
+            extensions.append(modname)
+        elif not filename.startswith(root):
+            unvendored[modname] = filename
+    return unvendored, extensions
+
+
+@contextlib.contextmanager
+def vendored(project, root=None):
+    """A context manager under which the vendored project will be imported."""
+    if root is None:
+        root = project_root(project)
+    # Add the vendored project directory, so that it gets tried first.
+    sys.path.insert(0, root)
+    try:
+        yield root
+    finally:
+        sys.path.remove(root)
+
+
+def preimport(project, modules, **kwargs):
+    """Import each of the named modules out of the vendored project."""
+    with vendored(project, **kwargs):
+        for name in modules:
+            import_module(name)