Vendor dependencies

Let's see how I like this workflow.

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

@@ -0,0 +1,51 @@
+# 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.
+
+# Resources for transitive deps, shared by C++ and Rust.
+ResourceInfo = provider(fields = [
+    # A map containing all resources from transitive dependencies.  The keys
+    # are rule labels and the values are maps of resource names (the name used
+    # to lookup the resource at runtime) and the actual resource artifact.
+    "resources",  # {"label": {str.type, ("artifact", ["hidden"])}}
+])
+
+def gather_resources(
+        label: "label",
+        resources: {str.type: ("artifact", ["_arglike"])} = {},
+        deps: ["dependency"] = []) -> {"label": {str.type: ("artifact", ["_arglike"])}}:
+    """
+    Return the resources for this rule and its transitive deps.
+    """
+
+    all_resources = {}
+
+    # Resources for self.
+    if resources:
+        all_resources[label] = resources
+
+    # Merge in resources for deps.
+    for dep in deps:
+        if ResourceInfo in dep:
+            all_resources.update(dep[ResourceInfo].resources)
+
+    return all_resources
+
+def create_resource_db(
+        ctx: "context",
+        name: str.type,
+        binary: "artifact",
+        resources: {str.type: ("artifact", ["_arglike"])}) -> "artifact":
+    """
+    Generate a resource DB for resources for the given binary, relativized to
+    the binary's working directory.
+    """
+
+    db = {
+        name: cmd_args(resource, delimiter = "").relative_to(binary, parent = 1)
+        for (name, (resource, _other)) in resources.items()
+    }
+    return ctx.actions.write_json(name, db)