builtin.size.fn-length

Field	Value
id	builtin.size.fn-length
severity	warn
category	size
scope	file
languages	rust, python, go, java, typescript, tsx, javascript
evaluator	builtin / fn_length

Long functions tend to bundle multiple responsibilities, hide branching complexity, and resist isolated testing. A function that doesn’t fit on a screen is a function that’s hard to reason about.

Thresholds

Configure under [size] in .sextant/config.toml:

[size]
fn_length_warn = 60
fn_length_error = 120

Setting	Default	Effect
fn_length_warn	60	Functions at or above this trigger a warn.
fn_length_error	120	Functions at or above this escalate to error.

The line count is from the function’s opening brace (or its def line in Python) through the closing brace. Blanks and comments inside the body count.

Fixing a finding

• Look for natural seams: a leading “set up” block, a middle “decide” block, a trailing “render/persist” block. Each is usually a candidate helper.
• Push branches into early returns; pull error mapping into a single tail expression.
• If a function manages too much state, consider promoting that state into a struct with methods.

See also

• builtin.complexity.cyclomatic — often correlated with length.
• builtin.size.param-count — long parameter lists are a related smell.
• Configuration → size.