Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tools/buck/prelude/linking/linkables.bzl

@@ -0,0 +1,53 @@
+# 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//utils:utils.bzl",
+    "expect",
+)
+load(
+    ":link_groups.bzl",
+    "LinkGroupLibInfo",
+)
+load(
+    ":link_info.bzl",
+    "MergedLinkInfo",
+)
+load(
+    ":linkable_graph.bzl",
+    "LinkableGraph",
+    "LinkableRootInfo",
+)
+load(
+    ":shared_libraries.bzl",
+    "SharedLibraryInfo",
+)
+
+# A record containing all provider types used for linking in the prelude.  This
+# is essentially the minimal subset of a "linkable" `dependency` that user rules
+# need to implement linking, and avoids needing functions to take the heavier-
+# weight `dependency` type.
+LinkableProviders = record(
+    link_group_lib_info = field(LinkGroupLibInfo.type),
+    linkable_graph = field(LinkableGraph.type),
+    merged_link_info = field(MergedLinkInfo.type),
+    shared_library_info = field(SharedLibraryInfo.type),
+    linkable_root_info = field([LinkableRootInfo.type, None], None),
+)
+
+def linkable(dep: "dependency") -> LinkableProviders.type:
+    expect(LinkGroupLibInfo in dep, str(dep.label.raw_target()))
+    return LinkableProviders(
+        shared_library_info = dep[SharedLibraryInfo],
+        linkable_graph = dep[LinkableGraph],
+        merged_link_info = dep[MergedLinkInfo],
+        link_group_lib_info = dep[LinkGroupLibInfo],
+        linkable_root_info = dep.get(LinkableRootInfo),
+    )
+
+def linkables(deps: ["dependency"]) -> [LinkableProviders.type]:
+    return [linkable(dep) for dep in deps if MergedLinkInfo in dep]