lab-03-complexity

permalink	/labs/lab-03-complexity/
title	Lab 03: Complexity Analysis
description	Analyze cyclomatic complexity across all 5 demo apps using Lizard and convert results to SARIF format.

Lab 03: Complexity Analysis

Duration	Level	Prerequisites
30 min	Intermediate	Lab 02

Learning Objectives

• Understand cyclomatic complexity (CCN) and why it matters
• Run Lizard to measure function-level complexity
• Interpret CCN scores, function length, and parameter counts
• Convert Lizard output to SARIF format using lizard-to-sarif.py
• Identify functions that exceed complexity thresholds

Prerequisites

• Completed Lab 02: Linting
• Lizard installed (pip install lizard)

Exercises

Exercise 1: Understand Cyclomatic Complexity

Cyclomatic complexity (CCN) measures the number of independent execution paths through a function. Higher CCN means more paths to test, harder-to-understand code, and higher defect probability.

CCN Range	Risk Level	Action
1–5	Low	Simple, easy to test
6–10	Moderate	Acceptable, consider refactoring
11–20	High	Should be refactored — CI warning
21+	Very High	Must be refactored — CI error

The workshop uses a threshold of 10 for the CI quality gate.

Exercise 2: Run Lizard Across All Apps

Working Directory: Run the following commands from the code-quality-scan-demo-app repository root.

Run Lizard across all demo apps to get a summary:

lizard cq-demo-app-001/src cq-demo-app-002/src cq-demo-app-003/src cq-demo-app-004/src cq-demo-app-005/ --CCN 10

Lizard outputs a table with these columns:

Column	Description
NLOC	Non-comment Lines of Code
CCN	Cyclomatic Complexity Number
Token	Token count
PARAM	Number of parameters
Length	Total function length in lines
Location	File path and function name

Exercise 3: Generate CSV Output

Generate CSV output for programmatic processing:

lizard cq-demo-app-001/src cq-demo-app-002/src cq-demo-app-003/src cq-demo-app-004/src cq-demo-app-005/ --csv > lizard-output.csv

View the first few lines of the CSV:

Get-Content lizard-output.csv | Select-Object -First 15

The CSV contains one row per function with columns: NLOC, CCN, Token, PARAM, Length, Location, File, Function, Start, End.

Exercise 4: Convert to SARIF Format

Use the lizard-to-sarif.py converter to transform Lizard CSV output into SARIF:

python src/converters/lizard-to-sarif.py --input lizard-output.csv --output complexity.sarif --ccn-threshold 10 --length-threshold 50

The converter creates a SARIF result for each function that exceeds either threshold:

• CCN > 10: Flagged as a complexity violation
• Length > 50 lines: Flagged as a function length violation

Examine the generated SARIF:

Get-Content complexity.sarif | ConvertFrom-Json | Select-Object -ExpandProperty runs | Select-Object -ExpandProperty results | Select-Object ruleId, level, @{N='function';E={$_.locations[0].physicalLocation.artifactLocation.uri}} | Format-Table

Exercise 5: Identify High-Complexity Functions

Filter for functions that exceed the CCN threshold:

lizard cq-demo-app-001/src cq-demo-app-002/src cq-demo-app-003/src cq-demo-app-004/src cq-demo-app-005/ --CCN 10 --warnings_only

For each flagged function, note:

1. Which function has high complexity
2. What causes it — nested if/else, switch statements, loops within loops
3. How to fix it — extract helper functions, use early returns, replace conditionals with lookup tables

Exercise 6: Analyze Nesting Depth

Look at the highest-complexity functions and identify nesting patterns:

lizard cq-demo-app-001/src cq-demo-app-002/src --CCN 15 --warnings_only -L 100

Common causes of high complexity:

Pattern	CCN Impact	Refactoring Strategy
Nested if/else chains	+1 per branch	Extract to guard clauses with early returns
switch with many cases	+1 per case	Use lookup table / dictionary
Loop + conditional	Multiplicative	Extract inner logic to a function
Try/catch with retry	+2–3	Extract retry logic to utility

Verification Checkpoint

Verify your work before continuing:

• Lizard ran successfully across all 5 demo apps
• You generated lizard-output.csv with function-level metrics
• You converted the CSV to complexity.sarif using lizard-to-sarif.py
• You identified at least 3 functions with CCN > 10
• You understand the difference between CCN and function length

Summary

Cyclomatic complexity analysis with Lizard provides function-level quality metrics that complement lint findings. High-CCN functions are harder to test, more error-prone, and difficult to maintain. By converting Lizard output to SARIF, you can track complexity trends alongside lint and coverage findings in a unified dashboard.

The workshop threshold of CCN ≤ 10 aligns with industry best practices. Functions exceeding this threshold should be refactored by extracting helper functions, using early returns, and replacing complex conditionals with lookup patterns.

Next Steps

Proceed to Lab 04: Duplication Detection.