fix: spill module mapping args to a file

Author: mattem

CHANGELOG.md

@@ -59,6 +59,8 @@ Unreleased changes template.
 * (pypi) The `ppc64le` is now pointing to the right target in the `platforms` package.
 * (gazelle) No longer incorrectly merge `py_binary` targets during partial updates in 
   `file` generation mode. Fixed in [#2619](https://github.com/bazelbuild/rules_python/pull/2619).
+* (gazelle) Don't collapse depsets to a list or into args when generating the modules mapping file.
+  Support spilling modules mapping args into a params file.
 
 {#v0-0-0-added}
 ### Added

gazelle/modules_mapping/def.bzl

@@ -25,18 +25,21 @@ module name doesn't match the wheel distribution name.
 
 def _modules_mapping_impl(ctx):
     modules_mapping = ctx.actions.declare_file(ctx.attr.modules_mapping_name)
-    args = ctx.actions.args()
     all_wheels = depset(
         [whl for whl in ctx.files.wheels],
         transitive = [dep[DefaultInfo].files for dep in ctx.attr.wheels] + [dep[DefaultInfo].data_runfiles.files for dep in ctx.attr.wheels],
     )
-    args.add("--output_file", modules_mapping.path)
+
+    args = ctx.actions.args()
+    args.use_param_file(param_file_arg = "@%s")
     if ctx.attr.include_stub_packages:
         args.add("--include_stub_packages")
+    args.add("--output_file", modules_mapping)
     args.add_all("--exclude_patterns", ctx.attr.exclude_patterns)
-    args.add_all("--wheels", [whl.path for whl in all_wheels.to_list()])
+    args.add_all("--wheels", all_wheels)
+
     ctx.actions.run(
-        inputs = all_wheels.to_list(),
+        inputs = all_wheels,
         outputs = [modules_mapping],
         executable = ctx.executable._generator,
         arguments = [args],

gazelle/modules_mapping/generator.py

@@ -152,6 +152,7 @@ def data_has_purelib_or_platlib(path):
     parser = argparse.ArgumentParser(
         prog="generator",
         description="Generates the modules mapping used by the Gazelle manifest.",
+        fromfile_prefix_chars="@",
     )
     parser.add_argument("--output_file", type=str)
     parser.add_argument("--include_stub_packages", action="store_true")