Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tools/buck/prelude/java/dex.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.
+
+DexLibraryInfo = provider(
+    fields = [
+        # the .dex.jar file. May be None if there were not any Java classes to dex. If None, the
+        # remaining fields should be ignored.
+        "dex",  # ["artifact", None]
+        # the names of the .class files that went into the DEX file
+        "class_names",  # ["artifact", None]
+        # resources that are referenced by the classes in this DEX file
+        "referenced_resources",  # ["artifact", None]
+        # a value that estimates how much space the code represented by this object will take up in
+        # a DEX file. The units for this estimate are not important, as long as they are consistent
+        # with those used when determining how secondary DEX files should be packed.
+        "weight_estimate",  # ["artifact", None]
+    ],
+)
+
+def get_dex_produced_from_java_library(
+        ctx: "context",
+        dex_toolchain: "DexToolchainInfo",
+        jar_to_dex: "artifact",
+        needs_desugar: bool.type = False,
+        desugar_deps: ["artifact"] = [],
+        weight_factor: int.type = 1) -> "DexLibraryInfo":
+    # TODO(T102963008) check whether the java_library actually contains any classes
+
+    d8_cmd = cmd_args(dex_toolchain.d8_command[RunInfo])
+
+    library_path = jar_to_dex.short_path
+    prefix = "dex/{}".format(library_path)
+    output_dex_file = ctx.actions.declare_output(prefix + ".dex.jar")
+    d8_cmd.add(["--output-dex-file", output_dex_file.as_output()])
+
+    d8_cmd.add(["--file-to-dex", jar_to_dex])
+    d8_cmd.add(["--android-jar", dex_toolchain.android_jar])
+
+    d8_cmd.add(["--intermediate", "--no-optimize", "--force-jumbo"])
+    if not needs_desugar:
+        d8_cmd.add("--no-desugar")
+    else:
+        desugar_deps_file = ctx.actions.write(prefix + "_desugar_deps_file.txt", desugar_deps)
+        d8_cmd.add(["--classpath-files", desugar_deps_file])
+        d8_cmd.hidden(desugar_deps)
+
+    referenced_resources_file = ctx.actions.declare_output(prefix + "_referenced_resources.txt")
+    d8_cmd.add(["--referenced-resources-path", referenced_resources_file.as_output()])
+
+    weight_estimate_file = ctx.actions.declare_output(prefix + "_weight_estimate.txt")
+    d8_cmd.add(["--weight-estimate-path", weight_estimate_file.as_output()])
+
+    d8_cmd.add(["--weight-factor", str(weight_factor)])
+
+    class_names_file = ctx.actions.declare_output(prefix + "_class_names.txt")
+    d8_cmd.add(["--class-names-path", class_names_file.as_output()])
+
+    min_sdk_version = getattr(ctx.attrs, "_dex_min_sdk_version", None) or getattr(ctx.attrs, "min_sdk_version", None)
+    if min_sdk_version:
+        d8_cmd.add(["--min-sdk-version", str(min_sdk_version)])
+
+    ctx.actions.run(
+        d8_cmd,
+        category = "d8",
+        identifier = "{}:{} {}".format(ctx.label.package, ctx.label.name, output_dex_file.short_path),
+    )
+
+    return DexLibraryInfo(
+        dex = output_dex_file,
+        class_names = class_names_file,
+        referenced_resources = referenced_resources_file,
+        weight_estimate = weight_estimate_file,
+    )