Vendor dependencies

Let's see how I like this workflow.

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

@@ -0,0 +1,33 @@
+# 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//:paths.bzl", "paths")
+load("@prelude//utils:utils.bzl", "expect", "from_named_set")
+
+def rust_attr_resources(ctx: "context") -> {str.type: ("artifact", ["_arglike"])}:
+    """
+    Return the resources provided by this rule, as a map of resource name to
+    a tuple of the resource artifact and any "other" outputs exposed by it.
+    """
+    resources = {}
+
+    for name, resource in from_named_set(ctx.attrs.resources).items():
+        if type(resource) == "artifact":
+            other = []
+        else:
+            info = resource[DefaultInfo]
+            expect(
+                len(info.default_outputs) == 1,
+                "expected exactly one default output from {} ({})"
+                    .format(resource, info.default_outputs),
+            )
+            [resource] = info.default_outputs
+            other = info.other_outputs
+
+        resources[paths.join(ctx.label.package, name)] = (resource, other)
+
+    return resources