Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tools/buck/prelude/python_bootstrap/python_bootstrap.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.
+
+PythonBootstrapSources = provider(fields = ["srcs"])
+
+PythonBootstrapToolchainInfo = provider(fields = ["interpreter"])
+
+def python_bootstrap_library_impl(ctx: "context") -> ["provider"]:
+    tree = {src.short_path: src for src in ctx.attrs.srcs}
+    output = ctx.actions.symlinked_dir("__{}__".format(ctx.attrs.name), tree)
+    return [
+        DefaultInfo(default_outputs = [output]),
+        PythonBootstrapSources(srcs = ctx.attrs.srcs),
+    ]
+
+def python_bootstrap_binary_impl(ctx: "context") -> ["provider"]:
+    """
+    Declares a Python binary that is intended to be used in scripts that
+    bootstrap other aspects of the Buck2 prelude. Python bootstrap binaries do
+    not use the Python toolchain and, as such, are highly restricted in what
+    they can and can't do. In particular, bootstrap binaries can only depend on
+    bootstrap libraries and can only consist of a single file.
+    """
+    run_tree_inputs = {}
+    run_tree_recorded_deps = {}  # For a better error message when files collide
+    for dep in ctx.attrs.deps:
+        dep_srcs = dep[PythonBootstrapSources].srcs
+        for src in dep_srcs:
+            if src.short_path in run_tree_recorded_deps:
+                original_dep = run_tree_recorded_deps[src.short_path]
+                fail("dependency `{}` and `{}` both declare a source file named `{}`, consider renaming one of these files to avoid collision".format(original_dep.label, dep.label, src.short_path))
+            run_tree_inputs[src.short_path] = src
+            run_tree_recorded_deps[src.short_path] = dep
+
+    run_tree = ctx.actions.symlinked_dir("__%s__" % ctx.attrs.name, run_tree_inputs)
+    output = ctx.actions.copy_file(ctx.attrs.main.short_path, ctx.attrs.main)
+
+    is_windows = ctx.attrs._target_os_type == "windows"
+    interpreter = ctx.attrs._python_bootstrap_toolchain[PythonBootstrapToolchainInfo].interpreter
+
+    run_args = cmd_args()
+    if is_windows:
+        run_args.add(ctx.attrs._win_python_wrapper[RunInfo])
+        run_args.add(run_tree)
+        run_args.add(interpreter)
+        run_args.add(output)
+    else:
+        run_args.add("/usr/bin/env")
+        run_args.add(cmd_args(run_tree, format = "PYTHONPATH={}"))
+        run_args.add(interpreter)
+        run_args.add(output)
+    return [DefaultInfo(default_outputs = [output]), RunInfo(args = run_args)]

vendor/cxx/tools/buck/prelude/python_bootstrap/tools/TARGETS.v2

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+prelude = native
+
+prelude.sh_binary(
+    name = "win_python_wrapper",
+    main = "win_python_wrapper.bat",
+    visibility = ["PUBLIC"],
+)

vendor/cxx/tools/buck/prelude/python_bootstrap/tools/win_python_wrapper.bat

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+@REM Copyright (c) Meta Platforms, Inc. and affiliates.
+@REM
+@REM This source code is licensed under both the MIT license found in the
+@REM LICENSE-MIT file in the root directory of this source tree and the Apache
+@REM License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+@REM of this source tree.
+
+:: A wrapper to set PYTHONPATH and run a python command with the specified interpreter
+:: First arg: paths to library that should be made available
+:: Second arg: path to python interpreter
+:: Third arg: path to python file that should be run
+:: Fourth and onwards: any other arg that should be passed
+@echo off
+
+:: See https://stackoverflow.com/questions/382587/how-to-get-batch-file-parameters-from-nth-position-on
+setlocal enabledelayedexpansion
+set args=;;;;;;%*
+set args=!args:;;;;;;%1 =!
+
+set PYTHONPATH=%1;
+%args%
+endlocal