How to Use Cody by Sourcegraph for Legacy Code Refactoring
Modernize legacy codebases using Cody by Sourcegraph — convert old patterns to modern idioms, extract functions, improve naming, and add type annotations. Covers safe incremental refactoring and regression prevention.
Implementation Steps
- 1
Map legacy codebase structure
Identify: hotspot files (most changes), dependency graphs, untested areas, and technical debt categories.
- 2
Prioritize refactoring targets
Rank by: change frequency × complexity × test coverage. High-change, complex, untested code first.
- 3
Generate refactored code in small PRs
Refactor one function or file per PR. Keep PRs under 200 lines changed. Ensure existing tests still pass.
- 4
Add tests before refactoring untested code
Generate characterization tests that capture current behavior before changing anything.
- 5
Review for behavioral equivalence
Verify refactored code produces identical outputs. Use property-based testing where possible.
Expected Metrics
Ehsan's Recommendation
The biggest refactoring mistake: changing everything at once. Cody by Sourcegraph makes it tempting to refactor an entire file because it is fast. Resist that temptation. Small PRs that change one thing are reviewable and revertable. Large refactoring PRs are neither. The companies successfully modernizing legacy code with AI do it in 200-line increments, not 2,000-line rewrites.
Ehsan Jahandarpour
AI Growth Strategist & Fractional CMO
Forbes Top 20 Growth Hacker · TEDx Speaker · 716 Academic Citations · Ex-Microsoft · CMO at FirstWave (ASX:FCT) · Forbes Communications Council