fix(rust): omit anonymous constants from graph symbol identity

Assisted-by: OpenAI Codex (GPT-6)

graphify/extractors/rust.py

@@ -262,6 +262,8 @@ def extract_rust(path: Path) -> dict:
             name_node = node.child_by_field_name("name")
             if name_node:
                 name = _read_text(name_node, source)
+                if t in ("static_item", "const_item") and name == "_":
+                    return
                 nid = _make_id(stem, name)
                 is_type = t in ("struct_item", "enum_item", "trait_item")
                 items_by_id.setdefault(nid, set()).add((is_type, name))
@@ -558,6 +560,8 @@ def extract_rust(path: Path) -> dict:
             name_node = node.child_by_field_name("name")
             if name_node:
                 item_name = _read_text(name_node, source)
+                if item_name == "_":
+                    return
                 line = node.start_point[0] + 1
                 if parent_impl_nid:
                     item_nid = _make_id(parent_impl_nid, item_name)

tests/test_rust_anonymous_const.py

@@ -0,0 +1,24 @@
+"""Anonymous Rust constants must not replace their owning file node."""
+
+from graphify.build import build_from_json
+from graphify.extract import extract
+
+
+def test_anonymous_constants_preserve_file_identity(tmp_path):
+    source = tmp_path / "codec.rs"
+    source.write_text(
+        "pub const WIDTH: usize = 8;\n"
+        "const _: () = assert!(WIDTH == 8);\n"
+        "const _: () = ();\n"
+        "static READY: bool = true;\n"
+        "pub fn encode() {}\n",
+        encoding="utf-8",
+    )
+    extracted = extract([source], root=tmp_path, cache_root=tmp_path / "cache")
+    graph = build_from_json(extracted, root=tmp_path, directed=False)
+
+    assert len({node["id"] for node in extracted["nodes"]}) == len(extracted["nodes"])
+    labels = {data["label"] for _, data in graph.nodes(data=True)}
+    assert {"codec.rs", "WIDTH", "READY", "encode()"} <= labels
+    assert "_" not in labels
+    assert all(source != target for source, target in graph.edges())