Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tools/buck/prelude/test/inject_test_run_info.bzl

@@ -0,0 +1,37 @@
+# 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.
+
+def inject_test_run_info(ctx: "context", test_info: ExternalRunnerTestInfo.type) -> ["provider"]:
+    # Access this here so we get failures in CI if we forget to inject it
+    # anywhere, regardless of whether an `env` is used.
+    inject_test_env = ctx.attrs._inject_test_env[RunInfo]
+
+    if (not test_info.env) or _exclude_test_env_from_run_info(ctx):
+        return [test_info, RunInfo(args = test_info.command)]
+
+    cell_root = ctx.label.cell_root
+
+    env_file = ctx.actions.write_json(
+        "test_env.json",
+        {
+            k: _maybe_relativize_path(test_info, cell_root, cmd_args(v, delimiter = " "))
+            for (k, v) in test_info.env.items()
+        },
+        with_inputs = True,
+    )
+
+    return [test_info, RunInfo(args = [inject_test_env, env_file, "--", test_info.command])]
+
+def _maybe_relativize_path(test_info: ExternalRunnerTestInfo.type, cell_root: "cell_root", arg: "cmd_args") -> "cmd_args":
+    if test_info.run_from_project_root:
+        return arg
+    return arg.relative_to(cell_root)
+
+def _exclude_test_env_from_run_info(ctx: "context"):
+    # Antlir assumes that $(exe ...) is a single, relative path, so if we make
+    # it multiple commands here, it'll break.
+    return "antlir_inner_test" in ctx.attrs.labels

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

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+prelude = native
+
+prelude.python_bootstrap_binary(
+    name = "inject_test_env",
+    main = "inject_test_env.py",
+    visibility = ["PUBLIC"],
+)

vendor/cxx/tools/buck/prelude/test/tools/inject_test_env.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python3
+# 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.
+
+import argparse
+import json
+import os
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument(
+        "env_file", help="A JSON file containing the environment to inject"
+    )
+    parser.add_argument("executable")
+    parser.add_argument("args", nargs="*")
+
+    args = parser.parse_args()
+
+    with open(args.env_file) as env_file:
+        env_from_file = json.load(env_file)
+        env = {**os.environ, **env_from_file}
+
+    os.execve(args.executable, [args.executable, *args.args], env)
+
+
+if __name__ == "__main__":
+    main()