Import pycross_wheel_library (#1403)

This patch imports a few files from jvolkman/rules_pycross at
757033ff8afeb5f7090b1320759f6f03d9c4615c.

I would like to re-use this rule for the `pypi_install` repo rule that
I'm working on. This rule extracts a downloaded wheel and generates an
appropriate `PyInfo` provider for it.

All the .pyfiles are taken as-is without modification. I had to run
buildifier
on all the bazel-related files. As per #1360,
that
meant that I had to add copyright headers.

A followup patch will make tweaks so that the code can be used from
within rules_python.

References: #1360

Author: philsc

third_party/rules_pycross/LICENSE

@@ -0,0 +1,201 @@
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third_party/rules_pycross/pycross/private/providers.bzl

@@ -0,0 +1,32 @@
+# Copyright 2023 Jeremy Volkman. All rights reserved.
+# Copyright 2023 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Pycross providers."""
+
+PycrossWheelInfo = provider(
+    doc = "Information about a Python wheel.",
+    fields = {
+        "name_file": "File: A file containing the canonical name of the wheel.",
+        "wheel_file": "File: The wheel file itself.",
+    },
+)
+
+PycrossTargetEnvironmentInfo = provider(
+    doc = "A target environment description.",
+    fields = {
+        "file": "The JSON file containing target environment information.",
+        "python_compatible_with": "A list of constraints used to select this platform.",
+    },
+)

third_party/rules_pycross/pycross/private/tools/BUILD.bazel

@@ -0,0 +1,53 @@
+# Copyright 2023 Jeremy Volkman. All rights reserved.
+# Copyright 2023 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+load("@rules_python//python:defs.bzl", "py_binary", "py_library", "py_test")
+
+package(default_visibility = ["//visibility:private"])
+
+py_library(
+    name = "namespace_pkgs",
+    srcs = [
+        "namespace_pkgs.py",
+    ],
+)
+
+py_test(
+    name = "namespace_pkgs_test",
+    size = "small",
+    srcs = [
+        "namespace_pkgs_test.py",
+    ],
+    tags = [
+        "unit",
+        # TODO(philsc): Make this work.
+        "manual",
+    ],
+    deps = [
+        ":namespace_pkgs",
+    ],
+)
+
+py_binary(
+    name = "wheel_installer",
+    srcs = ["wheel_installer.py"],
+    visibility = ["//visibility:public"],
+    deps = [
+        ":namespace_pkgs",
+        # TODO(philsc): Make this work with what's available in rules_python.
+        #"@rules_pycross_pypi_deps_absl_py//:pkg",
+        #"@rules_pycross_pypi_deps_installer//:pkg",
+    ],
+)

third_party/rules_pycross/pycross/private/tools/namespace_pkgs.py

@@ -0,0 +1,109 @@
+"""Utility functions to discover python package types"""
+import os
+import textwrap
+from pathlib import Path  # supported in >= 3.4
+from typing import List
+from typing import Optional
+from typing import Set
+
+
+def implicit_namespace_packages(
+    directory: str, ignored_dirnames: Optional[List[str]] = None
+) -> Set[Path]:
+    """Discovers namespace packages implemented using the 'native namespace packages' method.
+
+    AKA 'implicit namespace packages', which has been supported since Python 3.3.
+    See: https://packaging.python.org/guides/packaging-namespace-packages/#native-namespace-packages
+
+    Args:
+        directory: The root directory to recursively find packages in.
+        ignored_dirnames: A list of directories to exclude from the search
+
+    Returns:
+        The set of directories found under root to be packages using the native namespace method.
+    """
+    namespace_pkg_dirs: Set[Path] = set()
+    standard_pkg_dirs: Set[Path] = set()
+    directory_path = Path(directory)
+    ignored_dirname_paths: List[Path] = [Path(p) for p in ignored_dirnames or ()]
+    # Traverse bottom-up because a directory can be a namespace pkg because its child contains module files.
+    for dirpath, dirnames, filenames in map(
+        lambda t: (Path(t[0]), *t[1:]), os.walk(directory_path, topdown=False)
+    ):
+        if "__init__.py" in filenames:
+            standard_pkg_dirs.add(dirpath)
+            continue
+        elif ignored_dirname_paths:
+            is_ignored_dir = dirpath in ignored_dirname_paths
+            child_of_ignored_dir = any(
+                d in dirpath.parents for d in ignored_dirname_paths
+            )
+            if is_ignored_dir or child_of_ignored_dir:
+                continue
+
+        dir_includes_py_modules = _includes_python_modules(filenames)
+        parent_of_namespace_pkg = any(
+            Path(dirpath, d) in namespace_pkg_dirs for d in dirnames
+        )
+        parent_of_standard_pkg = any(
+            Path(dirpath, d) in standard_pkg_dirs for d in dirnames
+        )
+        parent_of_pkg = parent_of_namespace_pkg or parent_of_standard_pkg
+        if (
+            (dir_includes_py_modules or parent_of_pkg)
+            and
+            # The root of the directory should never be an implicit namespace
+            dirpath != directory_path
+        ):
+            namespace_pkg_dirs.add(dirpath)
+    return namespace_pkg_dirs
+
+
+def add_pkgutil_style_namespace_pkg_init(dir_path: Path) -> None:
+    """Adds 'pkgutil-style namespace packages' init file to the given directory
+
+    See: https://packaging.python.org/guides/packaging-namespace-packages/#pkgutil-style-namespace-packages
+
+    Args:
+        dir_path: The directory to create an __init__.py for.
+
+    Raises:
+        ValueError: If the directory already contains an __init__.py file
+    """
+    ns_pkg_init_filepath = os.path.join(dir_path, "__init__.py")
+
+    if os.path.isfile(ns_pkg_init_filepath):
+        raise ValueError("%s already contains an __init__.py file." % dir_path)
+
+    with open(ns_pkg_init_filepath, "w") as ns_pkg_init_f:
+        # See https://packaging.python.org/guides/packaging-namespace-packages/#pkgutil-style-namespace-packages
+        ns_pkg_init_f.write(
+            textwrap.dedent(
+                """\
+                # __path__ manipulation added by bazelbuild/rules_python to support namespace pkgs.
+                __path__ = __import__('pkgutil').extend_path(__path__, __name__)
+                """
+            )
+        )
+
+
+def _includes_python_modules(files: List[str]) -> bool:
+    """
+    In order to only transform directories that Python actually considers namespace pkgs
+    we need to detect if a directory includes Python modules.
+
+    Which files are loadable as modules is extension based, and the particular set of extensions
+    varies by platform.
+
+    See:
+    1. https://github.com/python/cpython/blob/7d9d25dbedfffce61fc76bc7ccbfa9ae901bf56f/Lib/importlib/machinery.py#L19
+    2. PEP 420 -- Implicit Namespace Packages, Specification - https://www.python.org/dev/peps/pep-0420/#specification
+    3. dynload_shlib.c and dynload_win.c in python/cpython.
+    """
+    module_suffixes = {
+        ".py",  # Source modules
+        ".pyc",  # Compiled bytecode modules
+        ".so",  # Unix extension modules
+        ".pyd",  # https://docs.python.org/3/faq/windows.html#is-a-pyd-file-the-same-as-a-dll
+    }
+    return any(Path(f).suffix in module_suffixes for f in files)