code-size

Code Size & Complexity Limits

Complexity is the strongest single predictor of defect density, and code written by agents balloons fastest — an agent under pressure adds one more branch to an existing function far more readily than it extracts a new one. These five SwiftLint threshold rules are the deterministic cap: they keep functions small enough that tests can actually cover their branches, and they keep agents from wrangling with their own tangles.

When This Skill Activates

Use this skill when:

• Setting up quality gates for a project where agents write most of the code
• A review keeps flagging "this function is too long/branchy" by hand
• Functions have grown past what their tests plausibly cover
• Adopting the deterministic gauntlet (see testing/fitness-functions/)

The Rules

The fragment at rules/swiftlint.yml configures five built-in SwiftLint rules (all enabled by default in SwiftLint — this fragment sets the thresholds):

Rule	Warning	Error	What it caps
cyclomatic_complexity	10	20	Independent paths through one function
function_body_length	50	100	Lines per function body
type_body_length	300	500	Lines per type body
file_length	500	1000	Lines per file
function_parameter_count	5	8	Parameters per function

Merge the fragment into the project's .swiftlint.yml (alongside any opt_in_rules/custom_rules fragments already adopted).

Brownfield Adoption: Baseline, Never Mass-Refactor

Turning these rules on in an existing codebase must not trigger a refactoring spree — bulk rewrites to satisfy a linter are how working code gets broken. Freeze today's violations and gate only new ones:

# One-time: record existing violations (SwiftLint 0.55+)
swiftlint lint --write-baseline .swiftlint-baseline.json

# The gate from then on — fails only on NEW violations
swiftlint lint --strict --baseline .swiftlint-baseline.json

Commit .swiftlint-baseline.json. Shrink it opportunistically: when touching a baselined function for other reasons, fix its violation and regenerate the baseline in the same commit.