Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tools/buck/prelude/python/toolchain.bzl

@@ -0,0 +1,77 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under both the MIT license found in the
+# LICENSE-MIT file in the root directory of this source tree and the Apache
+# License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+# of this source tree.
+
+load("@prelude//utils:platform_flavors_util.bzl", "by_platform")
+
+# The ways that Python exectuables handle native linkable dependencies.
+NativeLinkStrategy = enum(
+    # Statically links extensions into an embedded python binary
+    "native",
+    # Pull transitive native deps in as fully linked standalone shared libraries.
+    # This is typically the fastest build-time link strategy, as it requires no
+    # top-level context and therefore can shared build artifacts with all other
+    # binaries using this strategy.
+    "separate",
+    # Statically link all transitive native deps, which don't have an explicit
+    # dep from non-C/C++ code (e.g. Python), into a monolithic shared library.
+    # Native dep roots, which have an explicit dep from non-C/C++ code, remain
+    # as fully linked standalone shared libraries so that, typically, application
+    # code doesn't need to change to work with this strategy. This strategy
+    # incurs a relatively big build-time cost, but can significantly reduce the
+    # size of native code and number of shared libraries pulled into the binary.
+    "merged",
+)
+
+PackageStyle = enum(
+    "inplace",
+    "standalone",
+    "inplace_lite",
+)
+
+PythonToolchainInfo = provider(fields = [
+    "build_standalone_binaries_locally",
+    "compile",
+    # The interpreter to use to compile bytecode.
+    "host_interpreter",
+    "interpreter",
+    "version",
+    "native_link_strategy",
+    "generate_static_extension_info",
+    "package_style",
+    "make_source_db",
+    "make_source_db_no_deps",
+    "make_pex_inplace",
+    "make_pex_standalone",
+    "make_pex_modules",
+    "pex_executor",
+    "pex_extension",
+    "emit_omnibus_metadata",
+])
+
+# Stores "platform"/flavor name used to resolve *platform_* arguments
+PythonPlatformInfo = provider(fields = [
+    "name",
+])
+
+def get_platform_attr(
+        python_platform_info: "PythonPlatformInfo",
+        cxx_platform_info: "CxxPlatformInfo",
+        xs: [(str.type, "_a")]) -> ["_a"]:
+    """
+    Take a platform_* value, and the non-platform version, and concat into a list
+    of values based on the cxx/python platform
+    """
+    python_platform = python_platform_info.name
+    cxx_platform = cxx_platform_info.name
+    return by_platform([python_platform, cxx_platform], xs)
+
+python = struct(
+    PythonToolchainInfo = PythonToolchainInfo,
+    PythonPlatformInfo = PythonPlatformInfo,
+    PackageStyle = PackageStyle,
+    NativeLinkStrategy = NativeLinkStrategy,
+)