pr-splitter

name

pr-splitter

description

Split a large work-in-progress PR into a stack of small, reviewable PRs. Use this skill whenever the user mentions splitting a PR, stacking PRs, breaking up a large diff, making a PR easier to review, creating a PR stack, or decomposing changes into incremental commits. Also trigger when the user says things like "this PR is too big", "reviewers are struggling with this", or "I need to break this into smaller pieces". Works with any git-based project and any language.

PR Splitter

Split a large WIP PR into a stack of small, self-contained, reviewable PRs.

Philosophy

You are a curator, not a refactorer. The user worked fast — deep refactors, renames, breaking changes — and now needs it reviewable. Faithfully reproduce subsets of the existing diff as incremental slices.

• Copy changes exactly as they are. Never rewrite, restyle, or improve logic.
• Each slice must compile/build on its own (or at least not break the build).
• Each slice should be a coherent unit a reviewer can understand in isolation.
• Target 100–200 lines of meaningful code per slice (exclude tests, comments, blanks).
• Always include related tests with the code they test — never ship untested features.
• Order slices by module dependency: foundational changes first, consumers later.

Utilities Over Prompting

Use shell commands for all mechanical work. Do not read file contents into context or reason about diffs in prose when a utility can produce the answer directly.

Task	Use	Don't
Copy files	cp from worktree	Regenerate file content
Compare files	diff -q, diff -u	Read both files and reason about differences
Find what changed	git diff --stat, git diff --name-only	Parse diff output mentally
Extract one file's diff	awk on the saved full diff	Read entire diff into context
Check file coverage	comm on sorted file lists	Manually cross-check lists
Count LOC	grep/wc pipelines on diff output	Count lines by reading them
Apply partial changes	git apply --3way on extracted patch	Manually re-type code
Match branch to slice	grep the plan file	Re-read entire plan
Track progress	diff -rq against worktree	Ask the user what's done

Only use LLM reasoning for: understanding semantics, planning slice groupings, resolving ambiguous dependencies, and communicating with the user.

Read utility-patterns.md for copy-paste command recipes for every phase.

Workflow Overview

1. Init workspace: fetch diff, create worktree, generate manifests
2. Analyze: dependency graph + semantics (grep for imports, LLM for interpretation)
3. Plan slices, build file accounting, verify coverage with comm
4. Write .claude/pr-split-plan.md, iterate with user
5. Per slice:
   a. Orient: grep plan for current branch, determine slice number
   b. Write slice file list (.claude/slices/slice-N.tsv)
   c. Apply: cp/rm/git-apply per strategy
   d. Verify: diff each file against worktree
   e. Update plan, check remaining with diff -rq
6. Final: diff -rq working tree against worktree — should be empty
7. Cleanup: git worktree remove

Detailed Procedure

Phase 1: Initialize Workspace

When the user shares a PR link, extract the PR number and run:

mkdir -p .claude

# Fetch metadata — save as structured JSON for later jq queries
gh pr view <PR> --json baseRefName,headRefName,title,url,additions,deletions,number \
    > .claude/workspace-meta.json

# Fetch and save the full diff — source of truth for the entire process
gh pr diff <PR> > .claude/pr-full.diff

# File manifest with change types (A/M/D/R)
git fetch origin $(jq -r .baseRefName .claude/workspace-meta.json) \
                  $(jq -r .headRefName .claude/workspace-meta.json) --quiet
BASE=origin/$(jq -r .baseRefName .claude/workspace-meta.json)
HEAD=origin/$(jq -r .headRefName .claude/workspace-meta.json)
git diff --name-status "$BASE"..."$HEAD" > .claude/pr-files.tsv

# Per-file line counts for sizing estimates
git diff --numstat "$BASE"..."$HEAD" > .claude/pr-numstat.tsv

# Reference worktree — read-only copy of every file at PR head state
PR_HEAD_SHA=$(git rev-parse "$HEAD")
jq --arg sha "$PR_HEAD_SHA" '. + {head_sha: $sha}' .claude/workspace-meta.json \
    > .claude/workspace-meta.tmp && mv .claude/workspace-meta.tmp .claude/workspace-meta.json
git worktree add .claude/pr-head-worktree "$PR_HEAD_SHA" --detach --quiet

If gh is not available:

git fetch origin pull/<PR>/head:pr-head
BASE=origin/<base-branch>
HEAD=pr-head
# then same commands as above

Suggest adding .claude/ to .gitignore or .git/info/exclude.

Artifacts created:

• .claude/workspace-meta.json — PR metadata, head SHA
• .claude/pr-full.diff — complete diff
• .claude/pr-files.tsv — <change_type>\t<path> per changed file
• .claude/pr-numstat.tsv — <add>\t<del>\t<path> per file
• .claude/pr-head-worktree/ — detached worktree at PR head

Phase 2: Build the Dependency Graph

Extract import relationships mechanically, then interpret with LLM reasoning.

# Rust: find crate-internal imports in changed files
awk -F'\t' '{print $2}' .claude/pr-files.tsv | while read f; do
    [ -f ".claude/pr-head-worktree/$f" ] || continue
    imports=$(grep -cE '^use (crate|super|self)::' ".claude/pr-head-worktree/$f" 2>/dev/null || echo 0)
    [ "$imports" -gt 0 ] && echo "$f ($imports imports)" && \
        grep -nE '^use (crate|super|self)::' ".claude/pr-head-worktree/$f"
done

# TypeScript: find relative imports
awk -F'\t' '$2 ~ /\.(ts|tsx)$/ {print $2}' .claude/pr-files.tsv | while read f; do
    [ -f ".claude/pr-head-worktree/$f" ] || continue
    grep -nE "from ['\"]\.\.?/" ".claude/pr-head-worktree/$f" || true
done

Read dependency-analysis.md for more language patterns.

Use LLM to interpret the graph: identify roots (depended on by many), leaves (no internal deps), tightly coupled clusters.

Phase 3: Semantic Analysis

Read files from the worktree to understand roles:

# Overview: file types and change sizes
sort -t$'\t' -k1,1 -k3,3 .claude/pr-numstat.tsv

# Read specific file from PR head
cat .claude/pr-head-worktree/src/some_file.rs

# See a specific file's diff
awk '/^diff --git a\/src\/some_file.rs b\/src\/some_file.rs$/,/^diff --git /' \
    .claude/pr-full.diff | sed '$ d'

LLM reasoning is appropriate here: what each change does, which changes are coupled, how to group coherently.

Phase 4: Plan the Slices

Rules in priority order:

1. Compilability: no unresolvable references within a slice.
2. Test coverage: features ship with their tests.
3. Coherence: each slice tells a clear story to a reviewer.
4. Size: target 100–200 LOC. Estimate with numstat:

   awk -F'\t' '$3 ~ /types.rs|config.rs/ {sum += $1 + $2} END {print sum " LOC"}' \
       .claude/pr-numstat.tsv
   

5. Dependency order: topological sort — foundations first.

See SKILL.md section "Handling Common Patterns" in earlier versions, patterns still apply: renames with call-sites, type changes with consumers, new modules with tests, deletions with replacements, config in slice 1.

Phase 5: File Accounting

Create .claude/accounting.tsv:

# path	slice(s)
src/types.rs	1
src/handler.rs	2,4
src/new_module.rs	3
tests/test_handler.rs	4
old_module.rs	2

Verify 100% coverage using set operations:

# PR files (sorted, paths only)
awk -F'\t' '{print $NF}' .claude/pr-files.tsv | sort > /tmp/pr-files-sorted.txt

# Accounted files (sorted, unique paths)
awk -F'\t' '!/^#/ && NF>=2 {print $1}' .claude/accounting.tsv | sort -u > /tmp/accounted-sorted.txt

# Files in PR but not accounted for (must be empty)
comm -23 /tmp/pr-files-sorted.txt /tmp/accounted-sorted.txt

# Files accounted but not in PR (possible typos)
comm -13 /tmp/pr-files-sorted.txt /tmp/accounted-sorted.txt

Both comm outputs must be empty before proceeding.

Phase 6: Write the Plan and Iterate

Create .claude/pr-split-plan.md per plan-format.md. Include:

• Branch Map with suggested names: pr-split/01-<short-name>, pr-split/02-...
• Per-slice file lists with strategies
• File accounting table

Present to user, iterate until approved.

Phase 7: Extract Slices (One at a Time, Stacked)

Slices form a stack. The user manages branches (Graphite, git, etc.). Claude never creates branches, commits, or pushes.

7a. Orient

Determine where you are:

BRANCH=$(git branch --show-current)
echo "On: $BRANCH"

# Match branch to slice in plan
grep -n "$BRANCH" .claude/pr-split-plan.md || true

# Or find by slice number if branch name contains it
# e.g., pr-split/03-api → slice 3

# Quick progress count
grep -c 'Status.*done' .claude/pr-split-plan.md || echo "0 done"
grep -c 'Status.*pending' .claude/pr-split-plan.md || echo "0 pending"

# Worktree health
[ -d .claude/pr-head-worktree ] && echo "Worktree: OK" || echo "Worktree: MISSING"

If the worktree is missing:

git worktree add .claude/pr-head-worktree $(jq -r .head_sha .claude/workspace-meta.json) --detach

Record the actual branch name in the plan if it differs from the suggestion.

7b. Write the slice file list

Create .claude/slices/slice-N.tsv:

# strategy	path	[old_path]
copy	src/types.rs
copy	src/types_test.rs
delete	src/old_config.rs
rename	src/new_name.rs	src/old_name.rs
patch	src/handler.rs

Strategies:

• copy — file fully handled by this slice (or last slice touching it). cp from worktree.
• delete — git rm
• rename — cp new from worktree + git rm old
• patch — file split across slices; selective hunk application needed

7c. Apply the slice

Process the file list mechanically:

WT=.claude/pr-head-worktree

# Apply all 'copy' entries
awk -F'\t' '$1 == "copy" {print $2}' .claude/slices/slice-N.tsv | while read f; do
    mkdir -p "$(dirname "$f")"
    cp "$WT/$f" "$f"
    git add "$f"
done

# Apply all 'delete' entries
awk -F'\t' '$1 == "delete" {print $2}' .claude/slices/slice-N.tsv | while read f; do
    git rm -q "$f"
done

# Apply all 'rename' entries
awk -F'\t' '$1 == "rename" {print $2 "\t" $3}' .claude/slices/slice-N.tsv | while IFS=$'\t' read new old; do
    mkdir -p "$(dirname "$new")"
    cp "$WT/$new" "$new"
    git add "$new"
    git rm -q "$old" 2>/dev/null || true
done

7d. Handle patch-strategy files

For files split across slices — read partial-file-changes.md.

Quick version:

# Extract one file's diff from the saved full diff
awk '/^diff --git a\/src\/handler.rs b\/src\/handler.rs$/,/^diff --git /' \
    .claude/pr-full.diff | sed '$ d' > /tmp/handler.patch

# See the hunks
grep '^@@' /tmp/handler.patch

# Apply all hunks (if all belong to this slice)
git apply --3way /tmp/handler.patch

# Or filter to specific hunks first (by hunk number, 1-indexed)
awk '/^@@/{n++} n==0||n==1||n==3' /tmp/handler.patch > /tmp/handler-partial.patch
git apply --3way /tmp/handler-partial.patch

git add src/handler.rs

7e. Verify

# Files changed in this slice
git diff --name-only HEAD

# Per-file comparison against worktree
git diff --name-only HEAD | while read f; do
    if diff -q "$f" .claude/pr-head-worktree/"$f" 2>/dev/null; then
        echo "✅ $f"          # exact match — this file is at final state
    else
        echo "⚠️  $f (delta remains — OK if later slices touch it)"
        diff "$f" .claude/pr-head-worktree/"$f" | head -5
    fi
done

# File list cross-check: actual changes match planned files
PLANNED=$(awk -F'\t' '!/^#/ {print $2}' .claude/slices/slice-N.tsv | sort)
ACTUAL=$(git diff --name-only HEAD | sort)
comm -3 <(echo "$PLANNED") <(echo "$ACTUAL")
# Both columns should be empty

# Meaningful LOC (rough)
git diff HEAD -- ':(exclude)*test*' ':(exclude)*/tests/*' \
    | grep -c '^[+-]' | head -1

If anything fails, fix before reporting to user.

7f. Report to user

Brief: files applied, verification result, any warnings. Suggest a commit message.

7g. Update plan and track progress

Mark slice done in .claude/pr-split-plan.md. Update Branch Map actual column.

Track remaining work: