feat: add env var validators

reflex/config.py

@@ -15,6 +15,7 @@ from pathlib import Path
 from typing import (
     TYPE_CHECKING,
     Any,
+    Callable,
     Dict,
     Generic,
     List,
@@ -314,6 +315,8 @@ def interpret_env_var_value(
 
 T = TypeVar("T")
 
+VALIDATOR_TYPE = List[Callable[[T], None]]
+
 
 class EnvVar(Generic[T]):
     """Environment variable."""
@@ -321,18 +324,39 @@ class EnvVar(Generic[T]):
     name: str
     default: Any
     type_: T
+    validators: VALIDATOR_TYPE
 
-    def __init__(self, name: str, default: Any, type_: T) -> None:
+    def __init__(
+        self,
+        name: str,
+        default: Any,
+        type_: T,
+        validators: Optional[VALIDATOR_TYPE] = None,
+    ) -> None:
         """Initialize the environment variable.
 
         Args:
             name: The environment variable name.
             default: The default value.
             type_: The type of the value.
+            validators: The validators to apply to the value.
         """
         self.name = name
         self.default = default
         self.type_ = type_
+        self.validators = validators or []
+
+        self.validate(default)
+        self.validate(self.get())
+
+    def validate(self, value: T | None = None) -> None:
+        """Validate the environment variable.
+
+        Args:
+            value: The value to validate.
+        """
+        for validator in self.validators:
+            validator(value)
 
     def interpret(self, value: str) -> T:
         """Interpret the environment variable value.
@@ -381,6 +405,7 @@ class EnvVar(Generic[T]):
         Args:
             value: The value to set.
         """
+        self.validate(value)
         if value is None:
             _ = os.environ.pop(self.name, None)
         else:
@@ -395,16 +420,24 @@ class env_var:  # type: ignore
     name: str
     default: Any
     internal: bool = False
+    validators: VALIDATOR_TYPE
 
-    def __init__(self, default: Any, internal: bool = False) -> None:
+    def __init__(
+        self,
+        default: Any,
+        internal: bool = False,
+        validators: Optional[VALIDATOR_TYPE] = None,
+    ) -> None:
         """Initialize the descriptor.
 
         Args:
             default: The default value.
             internal: Whether the environment variable is reflex internal.
+            validators: The validators to apply to the value.
         """
         self.default = default
         self.internal = internal
+        self.validators = validators or []
 
     def __set_name__(self, owner, name):
         """Set the name of the descriptor.
@@ -429,17 +462,22 @@ class env_var:  # type: ignore
         env_name = self.name
         if self.internal:
             env_name = f"__{env_name}"
-        return EnvVar(name=env_name, default=self.default, type_=type_)
+        return EnvVar(
+            name=env_name, default=self.default, type_=type_, validators=self.validators
+        )
 
 
 if TYPE_CHECKING:
 
-    def env_var(default, internal=False) -> EnvVar:
+    def env_var(
+        default, internal=False, validators: Optional[VALIDATOR_TYPE[T]] = None
+    ) -> EnvVar[T]:
         """Typing helper for the env_var descriptor.
 
         Args:
             default: The default value.
             internal: Whether the environment variable is reflex internal.
+            validators: The validators to apply to the EnvVar.
 
         Returns:
             The EnvVar instance.

tests/units/test_config.py

@@ -248,11 +248,17 @@ def test_interpret_bool_env(value: str, expected: bool) -> None:
 
 
 def test_env_var():
+    def validate_positive(value: int) -> None:
+        if value < 0:
+            raise ValueError("Value must be positive")
+
     class TestEnv:
         BLUBB: EnvVar[str] = env_var("default")
         INTERNAL: EnvVar[str] = env_var("default", internal=True)
         BOOLEAN: EnvVar[bool] = env_var(False)
 
+        VALIDATE: EnvVar[int] = env_var(0, validators=[validate_positive])
+
     assert TestEnv.BLUBB.get() == "default"
     assert TestEnv.BLUBB.name == "BLUBB"
     TestEnv.BLUBB.set("new")
@@ -280,3 +286,9 @@ def test_env_var():
     assert TestEnv.BOOLEAN.get() is False
     TestEnv.BOOLEAN.set(None)
     assert "BOOLEAN" not in os.environ
+
+    assert TestEnv.VALIDATE.get() == 0
+    TestEnv.VALIDATE.set(1)
+    assert TestEnv.VALIDATE.get() == 1
+    with pytest.raises(ValueError):
+        TestEnv.VALIDATE.set(-1)