Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tools/buck/prelude/java/java_test.bzl

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+# 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//java:java_library.bzl", "build_java_library")
+load("@prelude//java:java_providers.bzl", "get_all_java_packaging_deps_tset")
+load("@prelude//java:java_toolchain.bzl", "JavaTestToolchainInfo", "JavaToolchainInfo")
+load("@prelude//java/utils:java_utils.bzl", "get_path_separator")
+load("@prelude//linking:shared_libraries.bzl", "SharedLibraryInfo", "merge_shared_libraries", "traverse_shared_library_info")
+load("@prelude//test/inject_test_run_info.bzl", "inject_test_run_info")
+
+def java_test_impl(ctx: "context") -> ["provider"]:
+    java_providers = build_java_library(ctx, ctx.attrs.srcs)
+    external_runner_test_info = build_junit_test(ctx, java_providers.java_library_info, java_providers.java_packaging_info)
+
+    return inject_test_run_info(ctx, external_runner_test_info) + [
+        java_providers.java_library_info,
+        java_providers.java_packaging_info,
+        java_providers.template_placeholder_info,
+        java_providers.default_info,
+    ]
+
+def build_junit_test(
+        ctx: "context",
+        tests_java_library_info: "JavaLibraryInfo",
+        tests_java_packaging_info: "JavaPackagingInfo",
+        extra_cmds: list.type = [],
+        extra_classpath_entries: ["artifact"] = []) -> ExternalRunnerTestInfo.type:
+    java_test_toolchain = ctx.attrs._java_test_toolchain[JavaTestToolchainInfo]
+
+    cmd = [ctx.attrs._java_toolchain[JavaToolchainInfo].java_for_tests] + extra_cmds + ctx.attrs.vm_args
+    classpath = []
+
+    if java_test_toolchain.use_java_custom_class_loader:
+        cmd.append("-Djava.system.class.loader=" + java_test_toolchain.java_custom_class_loader_class)
+        cmd.extend(java_test_toolchain.java_custom_class_loader_vm_args)
+        classpath.append(java_test_toolchain.java_custom_class_loader_library_jar)
+
+    classpath.extend(
+        [java_test_toolchain.test_runner_library_jar] +
+        [
+            get_all_java_packaging_deps_tset(ctx, java_packaging_infos = [tests_java_packaging_info])
+                .project_as_args("full_jar_args", ordering = "bfs"),
+        ] +
+        extra_classpath_entries,
+    )
+
+    labels = ctx.attrs.labels or []
+    run_from_cell_root = "buck2_run_from_cell_root" in labels
+    uses_java8 = "run_with_java8" in labels
+
+    classpath_args = cmd_args()
+    if run_from_cell_root:
+        classpath_args.relative_to(ctx.label.cell_root)
+
+    if uses_java8:
+        # Java 8 does not support using argfiles, and these tests can have huge classpaths so we need another
+        # mechanism to write the classpath to a file.
+        # We add "FileClassPathRunner" to the classpath, and then write a line-separated classpath file which we pass
+        # to the "FileClassPathRunner" as a system variable. The "FileClassPathRunner" then loads all the jars
+        # from that file onto the classpath, and delegates running the test to the junit test runner.
+        cmd.extend(["-classpath", cmd_args(java_test_toolchain.test_runner_library_jar)])
+        classpath_args.add(cmd_args(classpath))
+        classpath_args_file = ctx.actions.write("classpath_args_file", classpath_args)
+        cmd.append(cmd_args(classpath_args_file, format = "-Dbuck.classpath_file={}").hidden(classpath_args))
+    else:
+        # Java 9+ supports argfiles, so just write the classpath to an argsfile. "FileClassPathRunner" will delegate
+        # immediately to the junit test runner.
+        classpath_args.add("-classpath")
+        classpath_args.add(cmd_args(classpath, delimiter = get_path_separator()))
+        classpath_args_file = ctx.actions.write("classpath_args_file", classpath_args)
+        cmd.append(cmd_args(classpath_args_file, format = "@{}").hidden(classpath_args))
+
+    if (ctx.attrs.test_type == "junit5"):
+        cmd.extend(java_test_toolchain.junit5_test_runner_main_class_args)
+    elif (ctx.attrs.test_type == "testng"):
+        cmd.extend(java_test_toolchain.testng_test_runner_main_class_args)
+    else:
+        cmd.extend(java_test_toolchain.junit_test_runner_main_class_args)
+
+    if ctx.attrs.test_case_timeout_ms:
+        cmd.extend(["--default_test_timeout", ctx.attrs.test_case_timeout_ms])
+
+    class_names = ctx.actions.declare_output("class_names")
+    list_class_names_cmd = cmd_args([
+        java_test_toolchain.list_class_names[RunInfo],
+        "--jar",
+        tests_java_library_info.library_output.full_library,
+        "--output",
+        class_names.as_output(),
+    ])
+    ctx.actions.run(list_class_names_cmd, category = "list_class_names")
+
+    cmd.extend(["--test-class-names-file", class_names])
+
+    native_libs_env = _get_native_libs_env(ctx)
+    env = {}
+    for d in [ctx.attrs.env, native_libs_env]:
+        for key, value in d.items():
+            if key in env:
+                fail("Duplicate key for java_test env: '{}'".format(key))
+            env[key] = value
+
+    test_info = ExternalRunnerTestInfo(
+        type = "junit",
+        command = cmd,
+        env = env,
+        labels = ctx.attrs.labels,
+        contacts = ctx.attrs.contacts,
+        run_from_project_root = not run_from_cell_root,
+        use_project_relative_paths = not run_from_cell_root,
+    )
+    return test_info
+
+def _get_native_libs_env(ctx: "context") -> dict.type:
+    if not ctx.attrs.use_cxx_libraries:
+        return {}
+
+    if ctx.attrs.cxx_library_whitelist:
+        shared_library_infos = filter(None, [x.get(SharedLibraryInfo) for x in ctx.attrs.cxx_library_whitelist])
+    else:
+        shared_library_infos = filter(None, [x.get(SharedLibraryInfo) for x in ctx.attrs.deps])
+
+    shared_library_info = merge_shared_libraries(
+        ctx.actions,
+        deps = shared_library_infos,
+    )
+
+    native_linkables = traverse_shared_library_info(shared_library_info)
+    cxx_library_symlink_tree_dict = {so_name: shared_lib.lib.output for so_name, shared_lib in native_linkables.items()}
+    cxx_library_symlink_tree = ctx.actions.symlinked_dir("cxx_library_symlink_tree", cxx_library_symlink_tree_dict)
+
+    return {"BUCK_LD_SYMLINK_TREE": cxx_library_symlink_tree}