builtin.complexity.nesting

Field	Value
id	builtin.complexity.nesting
severity	warn
category	complexity
scope	file
languages	rust, python, go, java, typescript, tsx, javascript
evaluator	builtin / nesting

Deeply nested control flow (if inside for inside while inside another if…) is one of the strongest correlates with bug density. Each level of nesting multiplies the number of state combinations the reader has to track and shrinks the working memory left for the actual logic.

Thresholds

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

[complexity]
nesting_warn = 4
nesting_error = 6

Setting	Default	Effect
nesting_warn	4	Functions reaching this depth trigger a warn.
nesting_error	6	Functions reaching this depth escalate to error.

The depth is the maximum nesting level reached anywhere inside the function body. The function declaration itself counts as level 0.

Fixing a finding

• Invert conditions and return early — if !valid { return Err(_) } is one level shallower than if valid { ... }.
• Extract inner blocks into helpers — pull the innermost loop body into its own function and replace it with a single call.
• Use iterator chains over manual loops — iter().filter().map().sum() is a flat pipeline; the manual equivalent is at least two levels of nesting.
• Split combined predicates — if a && b && c reads better as guard clauses; if (a, b, c) == ... collapses many branches into one match.

See also

• builtin.complexity.cyclomatic — related metric on path count.
• Configuration → complexity.