Bypass f-string tag round-trip for var operation operands

packages/reflex-base/news/6747.performance.md

@@ -0,0 +1 @@
+`@var_operation` operands no longer pay the f-string tag round-trip (hash + permanent `_global_vars` registration + regex decode), cutting ~30-40% of var-operation construction cost and stopping internal operations from growing the never-evicting `_global_vars` dict.

packages/reflex-base/src/reflex_base/vars/base.py

@@ -930,6 +930,13 @@ def __format__(self, format_spec: str) -> str:
         Returns:
             The formatted var.
         """
+        # Operands of a running ``var_operation`` body interpolate as their
+        # raw JS expression: their VarData flows through the operation's
+        # ``_args``, so the tag round-trip (and its permanent ``_global_vars``
+        # entry) is pure overhead there. See ``var_operation``.
+        if self.__dict__.get("_format_without_tagging"):
+            return str(self)
+
         hashed_var = hash(self)
 
         _global_vars[hashed_var] = self
@@ -1941,10 +1948,34 @@ def wrapper(*args: P.args, **kwargs: P.kwargs) -> Var[T]:
             for key, value in kwargs.items()
         }
 
+        operands = [*args_vars.values(), *kwargs_vars.values()]
+        # Suppress f-string tagging for the operands while the body runs:
+        # their VarData reaches the operation through ``_args`` below, so the
+        # tag round-trip (hash + permanent ``_global_vars`` entry + regex
+        # decode of the return expression) is pure overhead. The suppression
+        # is ref-counted so a nested operation on the same var cannot clear
+        # an outer suppression early; vars created inside the body still tag
+        # normally and keep contributing VarData via the return expression.
+        for operand in operands:
+            operand_dict = operand.__dict__
+            operand_dict["_format_without_tagging"] = (  # pyright: ignore[reportIndexIssue]
+                operand_dict.get("_format_without_tagging", 0) + 1
+            )
+        try:
+            return_var = func(*args_vars.values(), **kwargs_vars)  # pyright: ignore [reportCallIssue]
+        finally:
+            for operand in operands:
+                operand_dict = operand.__dict__
+                remaining = operand_dict["_format_without_tagging"] - 1
+                if remaining:
+                    operand_dict["_format_without_tagging"] = remaining  # pyright: ignore[reportIndexIssue]
+                else:
+                    del operand_dict["_format_without_tagging"]  # pyright: ignore[reportIndexIssue]
+
         return CustomVarOperation.create(
             name=func.__name__,
             args=tuple(list(args_vars.items()) + list(kwargs_vars.items())),
-            return_var=func(*args_vars.values(), **kwargs_vars),  # pyright: ignore [reportCallIssue, reportReturnType]
+            return_var=return_var,  # pyright: ignore [reportArgumentType]
         ).guess_type()
 
     return wrapper

tests/units/vars/test_base.py

@@ -1,7 +1,16 @@
 from collections.abc import Mapping, Sequence
 
 import pytest
-from reflex_base.vars.base import computed_var, figure_out_type
+from reflex_base.utils.imports import ImportVar
+from reflex_base.vars.base import (
+    Var,
+    VarData,
+    _global_vars,
+    computed_var,
+    figure_out_type,
+    var_operation,
+    var_operation_return,
+)
 
 from reflex.state import State
 
@@ -66,6 +75,64 @@ class FancyTestStrVar(Var, python_types=FancyTestStr):
     )
 
 
+def test_var_operation_does_not_register_global_vars() -> None:
+    """Internal var operations bypass the f-string tag round-trip.
+
+    Regression: each operand interpolation hashed the var and permanently
+    registered it in the module-global ``_global_vars`` (a memory leak,
+    worst under hot-reload), then the return expression regex-decoded the
+    tag back out. Operand VarData already flows through
+    ``CustomVarOperation._args``.
+    """
+    lhs = Var(
+        _js_expr="tag_bypass_lhs",
+        _var_data=VarData(imports={"op-lib": [ImportVar(tag="thing")]}),
+    ).to(int)
+
+    before = len(_global_vars)
+    result = lhs + 1
+    assert len(_global_vars) == before
+
+    # The suppression flag does not persist on the operand after the op.
+    assert "_format_without_tagging" not in lhs.__dict__
+
+    # Operand VarData still reaches the merged operation VarData via _args.
+    var_data = result._get_all_var_data()
+    assert var_data is not None
+    assert dict(var_data.imports)["op-lib"] == (ImportVar(tag="thing"),)
+    assert str(result) == "(tag_bypass_lhs + 1)"
+
+    # Formatting outside an operation still registers (and tags) as before.
+    formatted = f"{lhs}"
+    assert len(_global_vars) == before + 1
+    assert formatted != str(lhs)
+
+
+def test_var_operation_body_created_vars_keep_var_data() -> None:
+    """Vars created inside an operation body still contribute their VarData.
+
+    Only the operands bypass tagging; a var constructed inside the body is
+    not carried by ``_args``, so it must keep flowing through the tagged
+    return expression.
+    """
+    from reflex_base.vars.number import NumberVar
+
+    @var_operation
+    def op_with_derived(value: NumberVar):
+        derived = Var(
+            _js_expr="derivedHelper",
+            _var_data=VarData(imports={"derived-lib": [ImportVar(tag="helper")]}),
+        )
+        return var_operation_return(f"({value} + {derived})", var_type=int)
+
+    result = op_with_derived(Var(_js_expr="a").to(int))
+
+    var_data = result._get_all_var_data()
+    assert var_data is not None
+    assert dict(var_data.imports)["derived-lib"] == (ImportVar(tag="helper"),)
+    assert str(result) == "(a + derivedHelper)"
+
+
 def test_computed_var_replace() -> None:
     class StateTest(State):
         @computed_var(cache=True)