Vendor dependencies

Let's see how I like this workflow.

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

@@ -0,0 +1,127 @@
+# 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//cxx:cxx_toolchain_types.bzl", "CxxPlatformInfo")
+load("@prelude//linking:shared_libraries.bzl", "traverse_shared_library_info")
+load("@prelude//utils:utils.bzl", "flatten")
+load(":interface.bzl", "PythonLibraryInterface", "PythonLibraryManifestsInterface")
+load(":manifest.bzl", "ManifestInfo")
+load(":toolchain.bzl", "PythonPlatformInfo", "get_platform_attr")
+
+PythonLibraryManifests = record(
+    label = field("label"),
+    srcs = field([ManifestInfo.type, None]),
+    src_types = field([ManifestInfo.type, None], None),
+    resources = field([(ManifestInfo.type, ["_arglike"]), None]),
+    bytecode = field([ManifestInfo.type, None]),
+    # A map of module name to to source artifact for Python extensions.
+    extensions = field([{str.type: "_a"}, None]),
+)
+
+def _bytecode_artifacts(value: PythonLibraryManifests.type):
+    if value.bytecode == None:
+        return []
+    return value.bytecode.artifacts
+
+def _bytecode_manifests(value: PythonLibraryManifests.type):
+    if value.bytecode == None:
+        return []
+    return value.bytecode.manifest
+
+def _hidden_resources(value: PythonLibraryManifests.type):
+    if value.resources == None:
+        return []
+    return value.resources[1]
+
+def _has_hidden_resources(children: [bool.type], value: [PythonLibraryManifests.type, None]):
+    if value:
+        if value.resources and len(value.resources[1]) > 0:
+            return True
+    return any(children)
+
+def _resource_manifests(value: PythonLibraryManifests.type):
+    if value.resources == None:
+        return []
+    return value.resources[0].manifest
+
+def _resource_artifacts(value: PythonLibraryManifests.type):
+    if value.resources == None:
+        return []
+    return value.resources[0].artifacts
+
+def _source_manifests(value: PythonLibraryManifests.type):
+    if value.srcs == None:
+        return []
+    return value.srcs.manifest
+
+def _source_artifacts(value: PythonLibraryManifests.type):
+    if value.srcs == None:
+        return []
+    return value.srcs.artifacts
+
+def _source_type_manifests(value: PythonLibraryManifests.type):
+    if value.src_types == None:
+        return []
+    return value.src_types.manifest
+
+def _source_type_artifacts(value: PythonLibraryManifests.type):
+    if value.src_types == None:
+        return []
+    return value.src_types.artifacts
+
+PythonLibraryManifestsTSet = transitive_set(
+    args_projections = {
+        "bytecode_artifacts": _bytecode_artifacts,
+        "bytecode_manifests": _bytecode_manifests,
+        "hidden_resources": _hidden_resources,
+        "resource_artifacts": _resource_artifacts,
+        "resource_manifests": _resource_manifests,
+        "source_artifacts": _source_artifacts,
+        "source_manifests": _source_manifests,
+        "source_type_artifacts": _source_type_artifacts,
+        "source_type_manifests": _source_type_manifests,
+    },
+    reductions = {
+        "has_hidden_resources": _has_hidden_resources,
+    },
+)
+
+# Information about a python library and its dependencies.
+# TODO(nmj): Resources in general, and mapping of resources to new paths too.
+PythonLibraryInfo = provider(fields = [
+    "manifests",  # PythonLibraryManifestsTSet
+    "shared_libraries",  # "SharedLibraryInfo"
+])
+
+def info_to_interface(info: PythonLibraryInfo.type) -> PythonLibraryInterface.type:
+    return PythonLibraryInterface(
+        shared_libraries = lambda: traverse_shared_library_info(info.shared_libraries),
+        iter_manifests = lambda: info.manifests.traverse(),
+        manifests = lambda: manifests_to_interface(info.manifests),
+        has_hidden_resources = lambda: info.manifests.reduce("has_hidden_resources"),
+        hidden_resources = lambda: [info.manifests.project_as_args("hidden_resources")],
+    )
+
+def manifests_to_interface(manifests: PythonLibraryManifestsTSet.type) -> PythonLibraryManifestsInterface.type:
+    return PythonLibraryManifestsInterface(
+        src_manifests = lambda: [manifests.project_as_args("source_manifests")],
+        src_artifacts = lambda: [manifests.project_as_args("source_artifacts")],
+        src_type_manifests = lambda: [manifests.project_as_args("source_manifests")],
+        src_type_artifacts = lambda: [manifests.project_as_args("source_artifacts")],
+        bytecode_manifests = lambda: [manifests.project_as_args("bytecode_manifests")],
+        bytecode_artifacts = lambda: [manifests.project_as_args("bytecode_artifacts")],
+        resource_manifests = lambda: [manifests.project_as_args("resource_manifests")],
+        resource_artifacts = lambda: [manifests.project_as_args("resource_artifacts")],
+    )
+
+def get_python_deps(ctx: "context"):
+    python_platform = ctx.attrs._python_toolchain[PythonPlatformInfo]
+    cxx_platform = ctx.attrs._cxx_toolchain[CxxPlatformInfo]
+    return flatten(
+        [ctx.attrs.deps] +
+        get_platform_attr(python_platform, cxx_platform, ctx.attrs.platform_deps),
+    )