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Fix rx.cond literal string typing #6545

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Fix rx.cond literal string typing #6545

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84ff913
Preserve literal string types in cond
Alek99 May 20, 2026
6a66f73
Address cond typing review feedback
Alek99 May 20, 2026
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20 changes: 20 additions & 0 deletions packages/reflex-components-core/src/reflex_components_core/core/cond.py
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
from reflex_base.vars import VarData
from reflex_base.vars.base import LiteralVar, Var
from reflex_base.vars.number import ternary_operation
from typing_extensions import LiteralString

from reflex_components_core.base.bare import Bare
from reflex_components_core.base.fragment import Fragment
Expand Down Expand Up @@ -131,6 +132,25 @@ def cond(condition: Any, c1: Any, c2: Component, /) -> Component: ... # pyright

T = TypeVar("T", covariant=True)
U = TypeVar("U", covariant=True)
LITERAL_STRING_S = TypeVar("LITERAL_STRING_S", bound=LiteralString)


@overload
def cond(
condition: Any, c1: LITERAL_STRING_S, c2: LITERAL_STRING_S, /
) -> Var[LITERAL_STRING_S]: ... # pyright: ignore [reportOverlappingOverload]


@overload
def cond(
condition: Any, c1: LITERAL_STRING_S, c2: Var[U], /
) -> Var[LITERAL_STRING_S | U]: ... # pyright: ignore [reportOverlappingOverload]


@overload
def cond(
condition: Any, c1: Var[T], c2: LITERAL_STRING_S, /
) -> Var[T | LITERAL_STRING_S]: ... # pyright: ignore [reportOverlappingOverload]


@overload
Expand Down
31 changes: 19 additions & 12 deletions tests/units/components/core/test_cond.py
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
import json
from typing import Any, Literal
from typing import Any, Literal, cast

import pytest
from reflex_base.components.component import Component
Expand Down Expand Up @@ -167,7 +167,8 @@ def test_cond_assert_types() -> None:
text_comp = Text.create("hello")
text_comp2 = Text.create("world")
var_int: Var[int] = LiteralVar.create(1)
var_str: Var[str] = LiteralVar.create("a")
literal_var_str = LiteralVar.create("a")
widened_var_str = cast(Var[str], literal_var_str)

# Component, Component -> Component
_ = assert_type(cond(True, text_comp, text_comp2), Component)
Expand All @@ -181,23 +182,29 @@ def test_cond_assert_types() -> None:
# non-component, Component -> Component
_ = assert_type(cond(True, "hello", text_comp), Component)

# T, T -> Var[T]
_ = assert_type(cond(True, "hello", "world"), Var[str])
# literal str, literal str -> Var[Literal[...]]
_ = assert_type(cond(True, "hello", "world"), Var[Literal["hello", "world"]])
Comment on lines +185 to +186
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@adhami3310 adhami3310 May 20, 2026

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it would be nice to have another test for T, T, now that strings are handled differently


# T, U -> Var[T | U]
_ = assert_type(cond(True, "hello", 3), Var[str | int])

# T, Var[T] -> Var[T]
_ = assert_type(cond(True, "hello", var_str), Var[str])
# literal str, literal Var[str] -> Var[Literal[...]]
_ = assert_type(cond(True, "hello", literal_var_str), Var[Literal["hello", "a"]])
Comment on lines +191 to +192
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@adhami3310 adhami3310 May 20, 2026

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the comments are confusing, literal str makes sense, but literal Var[str] when it's actually Var[LiteralString] is rather confusing


# Var[T], T -> Var[T]
_ = assert_type(cond(True, var_str, "world"), Var[str])
# literal Var[str], literal str -> Var[Literal[...]]
_ = assert_type(cond(True, literal_var_str, "world"), Var[Literal["a", "world"]])

# T, Var[U] -> Var[T | U]
_ = assert_type(cond(True, "hello", var_int), Var[str | int])
# literal str, Var[U] -> Var[Literal[...] | U]
_ = assert_type(cond(True, "hello", var_int), Var[int | Literal["hello"]])
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# Var[T], literal str -> Var[T]
_ = assert_type(cond(True, widened_var_str, "world"), Var[str])

# literal str, Var[U] -> Var[U]
_ = assert_type(cond(True, "hello", widened_var_str), Var[str])

# Var[T], U -> Var[T | U]
_ = assert_type(cond(True, var_str, 3), Var[int | Literal["a"]])
_ = assert_type(cond(True, widened_var_str, 3), Var[str | int])

# Var[T], Var[U] -> Var[T | U]
_ = assert_type(cond(True, var_int, var_str), Var[int | Literal["a"]])
_ = assert_type(cond(True, var_int, widened_var_str), Var[int | str])
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