find-duplication

Find Code Duplication

Detect duplicated or near-duplicate Go code and suggest consolidation candidates.

Rules

• Report findings, do not refactor. Refactoring is a separate task.
• Focus on production code (internal/, api/, cmd/). Skip test duplication unless explicitly asked.
• Group findings by severity: exact duplicates first, then near-duplicates.
• For each finding, state whether extraction is worth it or acceptable duplication.

Step 1: Determine Scope

Ask the user:

• Branch mode: only files changed in the current branch vs main.
• Full mode: scan the entire codebase.

For branch mode:

git diff --name-only upstream/main -- 'internal/' 'api/' 'cmd/' | grep '\.go$' | grep -v '_test\.go$'

For full mode, the target is internal/ api/ cmd/.

Step 2: Run dupl

Install and run dupl to find duplicate code blocks:

go install github.com/mibk/dupl@latest
dupl -threshold 15 <target>

-threshold 15 means at least 15 tokens of duplication. Lower values = more noise.

Review output and filter false positives:

• Import blocks (common imports are not duplication)
• Error constant declarations (repeated pattern is intentional)
• Single-line patterns (logging, error wrapping)
• Kubebuilder boilerplate (RBAC markers, webhook setup)

Step 3: Semantic Duplication Search

dupl only catches textual similarity. Also look for:

1. Similar function signatures — functions with near-identical parameter lists doing similar work across different packages.
2. Repeated error handling — same if err != nil { return fmt.Errorf(...) } pattern with slight variations.
3. Copy-pasted reconciler logic — similar reconciliation patterns across different controllers.
4. Duplicated struct definitions — similar structs in different packages (candidate for shared types).

Search for patterns:

# Find similar error wrapping
rg "fmt\.Errorf.*%w.*err\)" internal/ -A 1 -B 1

# Find similar reconciler patterns
rg "func.*Reconcile.*\(r reconciler\.Reconciler" internal/ -l

# Find similar asset generation
rg "func Generate.*\(r reconciler\.Reconciler" internal/ -l

Step 4: Check for Repeated Utilities

Look for utility functions that appear in multiple packages:

# Find GetSecretContent-like patterns
rg "func.*GetSecret" internal/ -l

# Find generation helpers
rg "func.*Generate.*Labels" internal/ -l

# Find comparison helpers
rg "func.*Equal\(" internal/ -l

These should be in internal/controller/utils/ or similar shared locations.

Step 5: Classify Findings

For each duplicate found, classify:

Step 6: Report

For each finding:

1. Files and line ranges involved
2. What is duplicated (brief description)
3. Token/line count
4. Classification (extract / parameterize / acceptable / boilerplate)
5. Suggested location for shared code (e.g., internal/controller/utils/)

Summary: total findings, how many actionable, estimated lines saved.