Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tools/buck/prelude/python/needed_coverage.bzl

@@ -0,0 +1,56 @@
+# 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")
+
+# All modules owned by a library. This will be used by top-level tests to find
+# paths that corresponds to the library.
+PythonNeededCoverageInfo = provider(fields = [
+    "modules",  # {str.type: str.type}
+])
+
+PythonNeededCoverage = record(
+    # A value from 0.0 to 1.0 indicating the ratio of coveraged code in the
+    # associated modules.
+    ratio = field(float.type),
+    # Modules that need to be covered.
+    modules = field([str.type]),
+)
+
+def _parse_python_needed_coverage_spec(
+        raw_spec: (int.type, "dependency", [str.type, None])) -> PythonNeededCoverage.type:
+    ratio_percentage, dep, specific_module = raw_spec
+
+    if ratio_percentage < 0 or ratio_percentage > 100:
+        fail("ratio_percentage must be between 0 and 100 (inclusive): {}".format(ratio_percentage))
+    ratio_percentage = ratio_percentage / 100.0
+
+    coverage = dep[PythonNeededCoverageInfo]
+    expect(coverage != None, "{} doesn't have a `PythonNeededCoverageInfo` provider", dep.label)
+
+    # Extract modules for this dep.
+    if specific_module != None:
+        module = coverage.modules.get(specific_module)
+        if module == None:
+            fail(
+                "module {} specified in needed_coverage not found in target {}"
+                    .format(specific_module, dep.label),
+            )
+        modules = [module]
+    else:
+        modules = coverage.modules.values()
+
+    expect(len(modules) > 0, "no modules found for {} ({})", dep.label, coverage)
+
+    return PythonNeededCoverage(
+        ratio = ratio_percentage,
+        modules = modules,
+    )
+
+def parse_python_needed_coverage_specs(
+        raw_specs: [(int.type, "dependency", [str.type, None])]) -> [PythonNeededCoverage.type]:
+    return [_parse_python_needed_coverage_spec(raw_spec) for raw_spec in raw_specs]