Allow log level enum with any case

When configuring a FastAPI application with debug logging, I used
"debug" instead of "DEBUG" in the configuration and was then annoyed
that the server didn't start with an error. The function call
supported a string with any case, but the Pydantic model we use to
validate most configurations required uppercase because it relied on
the enum to do the validation.

Implement a _missing_ method for the LogLevel enum that converts
strings in any case to the expected uppercase, which allows Pydantic
validation of models to work with any case of the log level and still
validates and returns the correct log level.

changelog.d/20231003_135049_rra_DM_23878.md

@@ -0,0 +1,3 @@
+### New features
+
+- Allow the `safir.logging.LogLevel` enum to be created from strings of any case, which will allow the logging level to be specified with any case for Safir applications that use Pydantic to validate the field.

src/safir/logging.py

@@ -7,7 +7,7 @@
 import re
 import sys
 from enum import Enum
-from typing import Any
+from typing import Any, Self
 
 import structlog
 from structlog.stdlib import add_log_level
@@ -48,14 +48,29 @@ class Profile(Enum):
 
 
 class LogLevel(Enum):
-    """Python logging level."""
+    """Python logging level.
+
+    Any case variation is accepted when converting a string to an enum value
+    via the class constructor.
+    """
 
     DEBUG = "DEBUG"
     INFO = "INFO"
     WARNING = "WARNING"
     ERROR = "ERROR"
     CRITICAL = "CRITICAL"
 
+    @classmethod
+    def _missing_(cls, value: Any) -> Self | None:
+        """Allow strings in any case to be used to create the enum."""
+        if not isinstance(value, str):
+            return None
+        value = value.upper()
+        for member in cls:
+            if member.value == value:
+                return member
+        return None
+
 
 def add_log_severity(
     logger: logging.Logger, method_name: str, event_dict: EventDict

tests/logging_test.py

@@ -14,6 +14,7 @@
 from _pytest.capture import CaptureFixture
 from _pytest.logging import LogCaptureFixture
 from httpx import AsyncClient
+from pydantic import BaseModel, ValidationError
 
 from safir import logging as safir_logging
 from safir.logging import LogLevel, Profile, configure_logging
@@ -48,6 +49,25 @@ def _strip_color(string: str) -> str:
     return re.sub(r"(?:\x1B[@-_]|[\x80-\x9F])[0-?]*[ -/]*[@-~]", "", string)
 
 
+def test_log_level_enum() -> None:
+    """Test that any case is allowed when initializing the enum."""
+    assert LogLevel("warning") == LogLevel.WARNING
+    assert LogLevel("WARNING") == LogLevel.WARNING
+    assert LogLevel("Error") == LogLevel.ERROR
+
+    # Check that this also works when going through Pydantic.
+    class Model(BaseModel):
+        log_level: LogLevel
+
+    model = Model.model_validate({"log_level": "warning"})
+    assert model.log_level == LogLevel.WARNING
+    model = Model.model_validate({"log_level": "inFO"})
+    assert model.log_level == LogLevel.INFO
+
+    with pytest.raises(ValidationError):
+        Model.model_validate({"log_level": "unknown"})
+
+
 def test_configure_logging_development(caplog: LogCaptureFixture) -> None:
     """Test that development-mode logging is key-value formatted."""
     caplog.set_level(logging.INFO)