Emit warnings when functions omitted when visualizing

docs/changelog.md

@@ -4,6 +4,7 @@ _This project uses semantic versioning_
 
 ## UNRELEASED
 
+- Emit warnings when functions omitted when visualizing [#336](https://github.com/egraphs-good/egglog-python/pull/336)
 ## 11.1.0 (2025-08-21)
 
 - Allow changing number of threads with env variable [#330](https://github.com/egraphs-good/egglog-python/pull/330)

python/egglog/egraph.py

@@ -23,6 +23,7 @@
     get_type_hints,
     overload,
 )
+from warnings import warn
 
 import graphviz
 from typing_extensions import Never, ParamSpec, Self, Unpack, assert_never
@@ -1024,6 +1025,12 @@ def _serialize(
             max_calls_per_function=max_calls_per_function,
             include_temporary_functions=include_temporary_functions,
         )
+        if serialized.discarded_functions:
+            msg = ", ".join(set(self._state.possible_egglog_functions(serialized.discarded_functions)))
+            warn(f"Omitted: {msg}", stacklevel=3)
+        if serialized.truncated_functions:
+            msg = ", ".join(set(self._state.possible_egglog_functions(serialized.truncated_functions)))
+            warn(f"Truncated: {msg}", stacklevel=3)
         if split_primitive_outputs or split_functions:
             additional_ops = set(map(self._callable_to_egg, split_functions))
             serialized.split_classes(self._egraph, additional_ops)

python/egglog/egraph_state.py

@@ -354,6 +354,14 @@ def op_mapping(self) -> dict[str, str]:
             if len(v) == 1
         }
 
+    def possible_egglog_functions(self, names: list[str]) -> Iterable[str]:
+        """
+        Given a list of egglog functions, returns all the possible Python function strings
+        """
+        for name in names:
+            for c in self.egg_fn_to_callable_refs[name]:
+                yield pretty_callable_ref(self.__egg_decls__, c)
+
     def typed_expr_to_egg(self, typed_expr_decl: TypedExprDecl, transform_let: bool = True) -> bindings._Expr:
         # transform all expressions with multiple parents into a let binding, so that less expressions
         # are sent to egglog. Only for performance reasons.

python/tests/test_high_level.py

@@ -958,6 +958,28 @@ def __hash__(self) -> int:
     assert hash(A()) == 42
 
 
+def test_serialize_warning_max_functions():
+    class A(Expr):
+        def __init__(self) -> None: ...
+
+    egraph = EGraph()
+    egraph.register(A())
+    with pytest.warns(UserWarning, match="A"):
+        egraph._serialize(max_functions=0)
+
+
+def test_serialize_warning_max_calls():
+    class A(Expr): ...
+
+    @function
+    def f(x: StringLike) -> A: ...
+
+    egraph = EGraph()
+    egraph.register(f("a"), f("b"))
+    with pytest.warns(UserWarning, match="f"):
+        egraph._serialize(max_calls_per_function=1)
+
+
 EXAMPLE_FILES = list((pathlib.Path(__file__).parent / "../egglog/examples").glob("*.py"))