DLC: PR Validity Analysis

Detect duplicate or redundant code introduced by a PR. Read-only analysis — no code modifications.

Before running, read ../dlc/references/ISSUE-TEMPLATE.md now for the issue format, and read ../dlc/references/REPORT-FORMAT.md now for the findings data structure.

Step 1: Resolve Target PR

Determine the PR to check and fetch all data needed for subsequent steps in a single call:

# If PR number provided as argument
PR_JSON=$(gh pr view <PR_NUMBER> --json number,title,url,headRefName,state,additions,changedFiles,files,body)

# If no argument — detect from current branch
PR_JSON=$(gh pr view --json number,title,url,headRefName,state,additions,changedFiles,files,body)

# Fetch repo identifier (used in Step 6 for issue creation)
REPO=$(gh repo view --json nameWithOwner -q .nameWithOwner)

# Display PR summary
echo "$PR_JSON" | jq '{number, title, url, headRefName, state, additions, changedFiles}'

If no open PR is found, abort with: "No open PR found for the current branch. Push your changes and open a PR first."

Large PR gate: If the PR has 500+ additions, use AskUserQuestion before proceeding:

• Present the addition count and file count (use changedFiles for the accurate total — .files | length caps at 100)
• Options: "Analyze everything" / "Only new files" / "Abort"
• If "Abort", stop and report: "PR validity analysis aborted by user."
• If "Only new files", limit Steps 2-3 to files with status added or renamed (skip modified)

Step 2: Fetch Diff & Extract Additions

Note: If the user selected "Only new files" in Step 1, restrict all diff parsing and construct extraction in this step to files where status == "added" or status == "renamed" (skip status == "modified").

Retrieve the full diff and extract new code constructs:

# Get the full diff (raw text — cannot be combined with the JSON call)
gh pr diff <PR_NUMBER>

# Get per-file status from the cached PR_JSON (no extra API call)
echo "$PR_JSON" | jq '.files[] | {path: .path, status: .status, additions: .additions}'

Parse the diff for + lines (excluding +++ b/ headers) and extract declarations:

Construct	Detection Pattern
Functions	function name(, const name = (, def name(, fn name(, func name(
Classes	class Name, struct Name, type Name struct
Components	export default function, export const Name, React/Vue component patterns
Methods	Indented function declarations inside class/struct bodies
Constants/Exports	export const, module.exports, top-level const/let/var with assignments

For each extracted construct, record:

• name: identifier name
• file: file path where it appears in the PR
• line: line number in the new file
• kind: function, class, component, method, constant
• signature: parameter list and return type (if available)
• body_snippet: first 5 lines of the body (for similarity matching)

Edge case: If no code additions are found (e.g., the PR only modifies docs, configs, or deletes code), create a single Info finding: "No new code constructs detected in PR diff — only non-code or deletion changes." Then skip to Step 7 (Report).

Step 3: Codebase Search

For each extracted construct, search the existing codebase for matches. Exclude files that are part of the PR diff.

Before targeted searches, launch an Explore agent with the following structured prompt:

Explore the codebase structure to identify where the following constructs
might have existing implementations. For each construct, report:

1. Directories most likely to contain similar code
2. Any files with matching or similar names
3. Related test files that might reveal expected behavior

Constructs to locate:
(list each construct name and kind extracted from Step 2)

Exclude these PR files from results:
(list each file path from the PR diff)

Use repomix-explorer (if available) for large codebases. Use the Explore agent output to prioritize directories for Steps 3a–3d. Then use Grep and Read for the targeted searches below.

3a. Name-Based Search

Use Grep to find constructs with the same name:

Grep: pattern="(function|const|class|def|fn|func|type)\s+{name}\b"

Exclude: node_modules, dist, build, .git, vendor directories, and the PR's own files.

3b. Signature Comparison

For each name match found in 3a:

1. Read the matched file around the match location (20 lines of context)
2. Compare parameter lists, return types, and overall structure
3. Score similarity: exact match, compatible (same params different order), or different

3c. Pattern-Based Search

Search for structural matches beyond exact names:

• Export names: Grep for the same export identifier
• Component structures: similar prop types, render patterns
• API endpoints: same route path or handler pattern

3d. Body-Based Search (Code Movement Detection)

For constructs where the PR also deletes code (file has both + and - lines):

1. Extract the body of the deleted construct
2. Grep for distinctive lines from the deleted body in the new location
3. If the new construct's body closely matches a deleted construct, classify as Code Movement (not duplication)

Self-match guard: When the deleted and added constructs are in the same file with overlapping line ranges, classify as Update (not Movement). Only flag Movement when code migrates between different files.

Step 4: Check Issue Reference

Check whether the PR references any GitHub issues:

# Extract PR body from the cached PR_JSON (no extra API call)
echo "$PR_JSON" | jq -r '.body'

Scan the PR body for #N issue references. For each referenced issue:

gh issue view <ISSUE_NUMBER> --json number,title,state,labels

Record the issue state (open/closed) and labels. This is informational only — produces Info-level findings if issues are referenced.

Step 5: Classify & Build Findings

For each construct extracted in Step 2, assign a classification based on the search results from Step 3:

Classification	Criteria	Severity
New	No match found in codebase	No finding
Duplicate	Name match + similar signature and body	Medium
Duplicate (divergent)	Name match, but different behavior or logic	High
Override	Replaces existing implementation in same file	No finding
Update	Modifies existing function (file was modified, not added)	No finding
Trivial Overlap	Name match only, completely different signature	Info
Code Movement	Body matches a deleted construct elsewhere	Info

All findings use type: redundancy.

Severity mapping (reinforced here for defense-in-depth):

Classification	Severity	Rationale
Duplicate (divergent)	High	Two implementations of the same name with different behavior — bug risk
Duplicate	Medium	Redundant code that should be consolidated
Trivial Overlap	Info	Name collision, no functional overlap — awareness only
Code Movement	Info	Intentional refactoring detected — informational

Step 6: User-Gated Issue Creation

Threshold: Create an issue only if there is any high finding OR 3+ medium findings.

If the threshold is not met, skip issue creation and proceed to Step 7.

If the threshold is met, use AskUserQuestion:

• Present the finding counts by severity
• Options: "Yes, create issue" / "No, skip" / "Show details first"
• If "Show details first", display each finding with file, line, classification, and matched location, then re-ask with the first two options
• If "No, skip", proceed to Step 7 without creating an issue

If the user approves issue creation, proceed:

Read ../dlc/references/ISSUE-TEMPLATE.md now and format the issue body exactly as specified.

Critical format rules (reinforced here):

• Title: [DLC] PR Validity: {n} redundancies in PR #{number}
• Label: dlc-pr-validity
• Body must contain: Scan Metadata table, Findings Summary table, Findings Detail grouped by severity, Recommended Actions
• In the Scan Metadata table, set Project Type to PR analysis (this skill is PR-focused and does not detect codebase project types)

Additional section — add after Findings Detail:

## Change Classification Summary

| Classification | Count | Files |
|---------------|-------|-------|
| New | {n} | {comma-separated file list} |
| Duplicate | {n} | {comma-separated file list} |
| Duplicate (divergent) | {n} | {comma-separated file list} |
| Override | {n} | {comma-separated file list} |
| Update | {n} | {comma-separated file list} |
| Trivial Overlap | {n} | {comma-separated file list} |
| Code Movement | {n} | {comma-separated file list} |
| **Total Constructs** | **{n}** | |

## Referenced Issues

| Issue | Title | State |
|-------|-------|-------|
| #{n} | {title} | {open/closed} |

> Omit this section if no issues were referenced in the PR body.

Raw Output: This skill has no CLI tool output to capture. Omit the Raw Output section from the issue body.

# $REPO was fetched in Step 1
TIMESTAMP=$(date +%s)
BODY_FILE="/tmp/dlc-issue-${TIMESTAMP}.md"

gh issue create \
  --repo "$REPO" \
  --title "[DLC] PR Validity: {n} redundancies in PR #{number}" \
  --body-file "$BODY_FILE" \
  --label "dlc-pr-validity"

If issue creation fails, save draft to /tmp/dlc-draft-${TIMESTAMP}.md and print the path.

If the user declines, skip issue creation and proceed to Step 7.

Step 7: Report

Print a summary:

PR validity analysis complete.
  - PR: #{number} ({title})
  - Constructs analyzed: {n}
  - Classifications: {n} new, {n} duplicate, {n} divergent, {n} override, {n} update, {n} trivial overlap, {n} code movement
  - Findings: {n} high, {n} medium, {n} info
  - Issue: #{number} ({url})  [only if created]
  - Referenced issues: #{n1} (open), #{n2} (closed)  [only if found in Step 4]