Vendor dependencies

Let's see how I like this workflow.

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

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+# 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//python:toolchain.bzl",
+    "PythonPlatformInfo",
+    "PythonToolchainInfo",
+)
+load(
+    "@prelude//python_bootstrap:python_bootstrap.bzl",
+    "PythonBootstrapToolchainInfo",
+)
+
+_INTERPRETER = select({
+    "ovr_config//os:linux": "python3",
+    "ovr_config//os:macos": "python3",
+    "ovr_config//os:windows": "python",
+})
+
+def _system_python_bootstrap_toolchain_impl(ctx):
+    return [
+        DefaultInfo(),
+        PythonBootstrapToolchainInfo(interpreter = ctx.attrs.interpreter),
+    ]
+
+# Creates a new bootstrap toolchain using Python that is installed on your system.
+# You may use it in your toolchain cell as follows:
+#
+# ```bzl
+# load("@prelude//toolchains:python.bzl", "system_python_bootstrap_toolchain")
+#
+# system_python_bootstrap_toolchain(
+#     name = "python_bootstrap", # the default name rules look for
+#     visibility = ["PUBLIC"],
+# )
+# ```
+system_python_bootstrap_toolchain = rule(
+    impl = _system_python_bootstrap_toolchain_impl,
+    attrs = {
+        "interpreter": attrs.string(default = _INTERPRETER),
+    },
+    is_toolchain_rule = True,
+)
+
+def _system_python_toolchain_impl(ctx):
+    """
+    A very simple toolchain that is hardcoded to the current environment.
+    """
+
+    return [
+        DefaultInfo(),
+        PythonToolchainInfo(
+            make_source_db = ctx.attrs.make_source_db[RunInfo],
+            make_source_db_no_deps = ctx.attrs.make_source_db_no_deps[RunInfo],
+            host_interpreter = RunInfo(args = [ctx.attrs.interpreter]),
+            interpreter = RunInfo(args = [ctx.attrs.interpreter]),
+            make_pex_modules = ctx.attrs.make_pex_modules[RunInfo],
+            make_pex_inplace = ctx.attrs.make_pex_inplace[RunInfo],
+            compile = RunInfo(args = ["echo", "COMPILEINFO"]),
+            package_style = "inplace",
+            native_link_strategy = "merged",
+        ),
+        PythonPlatformInfo(name = "x86_64"),
+    ]
+
+system_python_toolchain = rule(
+    impl = _system_python_toolchain_impl,
+    attrs = {
+        "interpreter": attrs.string(default = _INTERPRETER),
+        "make_pex_inplace": attrs.default_only(attrs.dep(providers = [RunInfo], default = "prelude//python/tools:make_pex_inplace")),
+        "make_pex_modules": attrs.default_only(attrs.dep(providers = [RunInfo], default = "prelude//python/tools:make_pex_modules")),
+        "make_source_db": attrs.default_only(attrs.dep(providers = [RunInfo], default = "prelude//python/tools:make_source_db")),
+        "make_source_db_no_deps": attrs.default_only(attrs.dep(providers = [RunInfo], default = "prelude//python/tools:make_source_db_no_deps")),
+    },
+    is_toolchain_rule = True,
+)