complexity-reduction

Complexity reduction

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Cyclomatic complexity counts linearly independent paths through a method: every if, else if, for, while, case, catch, &&, ||, and ?: adds one. High complexity means many paths to test and maintain. CodeFactor enforces a threshold on the PR diff; the local complexity:gate does the same before push.

When to use

• CodeFactor reports Complex Method on your PR.
• npm run complexity:gate fails (a changed method grew, or a new method exceeds the cap).
• You are about to add branching to an already-large method.

Diagnose first

Identify which methods are over the threshold and whether you introduced them:

npx eslint --no-config-lookup --format json \
  --rule '{"complexity": ["error", 15]}' <file>                 # per-method complexity

git show <base>:<file> | npx eslint --no-config-lookup --format json \
  --stdin --stdin-filename <file> --rule '{"complexity": ["error", 15]}'   # baseline (was it already complex?)

Rule-only runs must pass --no-config-lookup (ESLint 9 otherwise merges the repo config into the run) and --format json (the text formatters are not stable to parse).

Baseline gotcha: the gate is self-referential on main

complexity:gate defaults its baseline to the merge base with origin/main. That is correct on a feature branch, but on main itself the merge base is HEAD, so every violation reads "unchanged from baseline" and the gate always reports ok. When auditing on main, or after a merge, measure against the actually landed state:

git fetch origin
npm run complexity:gate -- --base origin/main

A failed gate names the skill to consult (this file); CodeFactor enforces the same cap on PR diffs even for methods unchanged from the baseline when their file is in the diff — reduce them anyway.

If a flagged method is unchanged from the baseline it is pre-existing debt, but CodeFactor still requires it under the threshold when the file is in the diff — reduce it anyway (it is a reviewable improvement, not a no-op).