Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tools/buck/prelude/apple/apple_dsym.bzl

@@ -0,0 +1,35 @@
+# 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//apple:apple_toolchain_types.bzl", "AppleToolchainInfo")
+
+DSYM_SUBTARGET = "dsym"
+DEBUGINFO_SUBTARGET = "debuginfo"
+
+AppleDebuggableInfo = provider(fields = [
+    "dsyms",  # ["artifact"]
+    "external_debug_info",  # ["_arglike"]
+])
+
+# TODO(T110672942): Things which are still unsupported:
+# - pass in dsymutil_extra_flags
+# - oso_prefix
+# - dsym_verification
+def get_apple_dsym(ctx: "context", executable: "artifact", external_debug_info: ["_arglike"], action_identifier: "string") -> "artifact":
+    dsymutil = ctx.attrs._apple_toolchain[AppleToolchainInfo].dsymutil
+    output = ctx.actions.declare_output("{}.dSYM".format(executable.short_path))
+
+    cmd = cmd_args([dsymutil, "-o", output.as_output(), executable])
+
+    # Mach-O executables don't contain DWARF data.
+    # Instead, they contain paths to the object files which themselves contain DWARF data.
+    #
+    # So, those object files are needed for dsymutil to be to create the dSYM bundle.
+    cmd.hidden(external_debug_info)
+    ctx.actions.run(cmd, category = "apple_dsym", identifier = action_identifier)
+
+    return output