ALL-ERRO0003 · vanilla_error_type

Count failures raised as the language base error rather than as a named one.

This is a deterministic rule for all languages. Read its implementation.

Definition

Read every raise one declaration states, take the type it names, and report the ones that name the base error the language ships. That is Exception and BaseException in Python, Error in JavaScript and TypeScript, Throwable and RuntimeException in Java, and std::exception in C++. A name that arrives qualified is judged on its last segment, so builtins.Exception reads the same as Exception.

The cost lands on the caller rather than on the raiser. Handling this one failure means catching the base type, which also catches the typo, the missing key, and the bug three frames down, so the caller either swallows defects it never meant to see or gives up on recovery and lets everything through. A named type costs one line to declare and it turns the catch into a statement about what went wrong instead of a statement about anything at all going wrong.

Evidence

Each finding names the declaration, the raise, and the base type it constructs. The value is the number of raises a caller cannot single out.

Exceptions

A bare re-raise carries the original type forward and constructs nothing, so it is left alone, and so is a raise of a value the code already holds such as a failure it caught a line above. The base names are a setting, because a project that declares its own root error may want that name reported too, and a language MCMR has not met yet spells its base differently. Only a callable is judged, because a type reaches every raise it owns through the callable holding it and would otherwise report the same one twice. base_errors is that list of names.

Examples

Bad

def load(path):
    if not path.exists():
        raise Exception(f"{path} is missing")

Good

def load(path):
    if not path.exists():
        raise ProfileMissing(path)

References

• Generalizes Ruff TRY002 raise-vanilla-class. Open reference
• Cites Pylint W0719 broad-exception-raised. Open reference
• Cites “The Python Tutorial”, user defined exceptions. Open reference
• Cites “Clean Code”, chapter 7, define exceptions in terms of a caller’s needs