Vendor dependencies

Let's see how I like this workflow.

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

@@ -0,0 +1,82 @@
+# 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")
+load("@prelude//cxx:headers.bzl", "CxxHeadersLayout", "CxxHeadersNaming")
+load("@prelude//utils:utils.bzl", "value_or")
+load(":apple_target_sdk_version.bzl", "get_min_deployment_version_for_node")
+
+_VERSION_PLACEHOLDER = "(VERSION)"
+
+# TODO(T115177501): Make target triples part of the toolchains
+# Map from SDK name -> target triple _without_ leading architecture
+_TARGET_TRIPLE_MAP = {
+    "iphoneos": "apple-ios{}".format(_VERSION_PLACEHOLDER),
+    "iphonesimulator": "apple-ios{}-simulator".format(_VERSION_PLACEHOLDER),
+    "macosx": "apple-macosx{}".format(_VERSION_PLACEHOLDER),
+    "watchos": "apple-watchos{}".format(_VERSION_PLACEHOLDER),
+    "watchsimulator": "apple-watchos{}-simulator".format(_VERSION_PLACEHOLDER),
+}
+
+def get_apple_cxx_headers_layout(ctx: "context") -> CxxHeadersLayout.type:
+    namespace = value_or(ctx.attrs.header_path_prefix, ctx.attrs.name)
+    return CxxHeadersLayout(namespace = namespace, naming = CxxHeadersNaming("apple"))
+
+def get_module_name(ctx: "context") -> str.type:
+    return ctx.attrs.module_name or ctx.attrs.header_path_prefix or ctx.attrs.name
+
+def has_apple_toolchain(ctx: "context") -> bool.type:
+    return hasattr(ctx.attrs, "_apple_toolchain")
+
+def get_versioned_target_triple(ctx: "context") -> str.type:
+    apple_toolchain_info = ctx.attrs._apple_toolchain[AppleToolchainInfo]
+    swift_toolchain_info = apple_toolchain_info.swift_toolchain_info
+
+    architecture = swift_toolchain_info.architecture
+    if architecture == None:
+        fail("Need to set `architecture` field of swift_toolchain(), target: {}".format(ctx.label))
+
+    target_sdk_version = get_min_deployment_version_for_node(ctx) or ""
+
+    sdk_name = apple_toolchain_info.sdk_name
+    target_triple_with_version_placeholder = _TARGET_TRIPLE_MAP.get(sdk_name)
+    if target_triple_with_version_placeholder == None:
+        fail("Could not find target triple for sdk = {}".format(sdk_name))
+
+    versioned_target_triple = target_triple_with_version_placeholder.replace(_VERSION_PLACEHOLDER, target_sdk_version)
+    return "{}-{}".format(architecture, versioned_target_triple)
+
+def expand_relative_prefixed_sdk_path(
+        sdk_path: "cmd_args",
+        swift_resource_dir: "cmd_args",
+        path_to_expand: str.type) -> "cmd_args":
+    path_expansion_map = {
+        "$RESOURCEDIR": swift_resource_dir,
+        "$SDKROOT": sdk_path,
+    }
+    expanded_cmd = cmd_args()
+    for (path_variable, path_value) in path_expansion_map.items():
+        if path_to_expand.startswith(path_variable):
+            path = path_to_expand[len(path_variable):]
+            if path.find("$") == 0:
+                fail("Failed to expand framework path: {}".format(path))
+            expanded_cmd.add(cmd_args([path_value, path], delimiter = ""))
+
+    return expanded_cmd
+
+def get_disable_pch_validation_flags() -> [str.type]:
+    """
+    We need to disable PCH validation for some actions like Swift compilation and Swift PCM generation.
+    Currently, we don't have a mechanism to compile with enabled pch validation and Swift explicit modules,
+    which we need to be able to do while we are waiting for Anonymous targets which will allow us to solve this problem properly.
+    """
+    return [
+        "-Xcc",
+        "-Xclang",
+        "-Xcc",
+        "-fno-validate-pch",
+    ]