From fbffb5a82324545c3985d0a64fca9d641bab5eff Mon Sep 17 00:00:00 2001
From: Mergen Nachin <mnachin@meta.com>
Date: Mon, 28 Sep 2026 18:07:01 -0400
Subject: [PATCH] [exir] Allow additional flatc options to preserve Vulkan
 signed zero

flatc omits scalar fields equal to their schema default. Because -0.0 == 0.0, a negative-zero Double is dropped and deserializes as +0.0. _flatc_compile gains flatc_additional_args, matching the decompiler API, to pass --force-defaults, and the Vulkan serializer opts in so signed zeros survive the round trip. Other flatbuffer users are unchanged.

Authored with OpenAI Codex; split planned with Claude Code.
---
 backends/vulkan/serialization/vulkan_graph_serialize.py | 2 +-
 backends/vulkan/test/test_serialization.py              | 8 ++++++++
 exir/_serialize/_flatbuffer.py                          | 9 ++++++++-
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/backends/vulkan/serialization/vulkan_graph_serialize.py b/backends/vulkan/serialization/vulkan_graph_serialize.py
index 665c23b8df2..8707ad53f50 100644
--- a/backends/vulkan/serialization/vulkan_graph_serialize.py
+++ b/backends/vulkan/serialization/vulkan_graph_serialize.py
@@ -110,7 +110,7 @@ def convert_to_flatbuffer(vk_graph: VkGraph) -> bytes:
         json_path = os.path.join(d, "schema.json")
         with open(json_path, "wb") as json_file:
             json_file.write(vk_graph_json.encode("ascii"))
-        _flatc_compile(d, schema_path, json_path)
+        _flatc_compile(d, schema_path, json_path, ["--force-defaults"])
         output_path = os.path.join(d, "schema.bin")
         with open(output_path, "rb") as output_file:
             return output_file.read()
diff --git a/backends/vulkan/test/test_serialization.py b/backends/vulkan/test/test_serialization.py
index 540b86ace82..8b95b1df2a1 100644
--- a/backends/vulkan/test/test_serialization.py
+++ b/backends/vulkan/test/test_serialization.py
@@ -372,6 +372,14 @@ def test_serialize_deserialize_non_finite_scalars(self) -> None:
             ]
         )
 
+    def test_serialize_deserialize_signed_zero(self) -> None:
+        values = [
+            VkValue(Double(-0.0)),
+            VkValue(Double(0.0)),
+            VkValue(DoubleList([-0.0, 0.0])),
+        ]
+        self.assertEqual(repr(self._round_trip(values).values), repr(values))
+
     def test_serialize_deserialize_non_finite_floats_in_list(self) -> None:
         # json only emits a float as a chunk of its own inside an object; in a
         # list the chunk carries the delimiter with it, so a rewrite that works
diff --git a/exir/_serialize/_flatbuffer.py b/exir/_serialize/_flatbuffer.py
index eaf7f296e55..4d015b84a80 100644
--- a/exir/_serialize/_flatbuffer.py
+++ b/exir/_serialize/_flatbuffer.py
@@ -369,7 +369,12 @@ def convert(value: object) -> object:
     return json.dumps(convert(json.loads(content))).encode("utf-8")
 
 
-def _flatc_compile(output_dir: str, schema_path: str, json_path: str) -> None:
+def _flatc_compile(
+    output_dir: str,
+    schema_path: str,
+    json_path: str,
+    flatc_additional_args: Optional[List[str]] = None,
+) -> None:
     """Serializes JSON data to a binary flatbuffer file.
 
     Args:
@@ -381,6 +386,7 @@ def _flatc_compile(output_dir: str, schema_path: str, json_path: str) -> None:
             matches the schema. Rewritten in place if it contains non-finite
             floats; flatc derives the output filename from this path, so the
             data cannot be sanitized into a differently-named file.
+        flatc_additional_args: Additional options passed to flatc.
     """
     with open(json_path, "rb") as json_file:
         content = json_file.read()
@@ -392,6 +398,7 @@ def _flatc_compile(output_dir: str, schema_path: str, json_path: str) -> None:
     _run_flatc(
         [
             "--binary",
+            *(flatc_additional_args or []),
             "-o",
             output_dir,
             schema_path,