Using JJ Workspaces

You're helping set up an isolated jj workspace for parallel development work without disrupting the current workspace.

Core Workflow: Systematic Directory Selection + Safety Verification

1. Directory Selection (Priority Order)

Check for workspace directory preferences in this order:

1. First: Check if .workspaces/ or workspaces/ directory exists in project root
2. Second: Review CLAUDE.md or similar project documentation for workspace preferences
3. Third: If neither exists, ask the user:
   • Option A: Create project-local directory (.workspaces/ or workspaces/)
   • Option B: Use global location (e.g., ~/workspaces/)

Never assume - always follow this priority system.

2. Safety Verification (CRITICAL for project-local directories)

If using a project-local directory (.workspaces/, workspaces/, etc.):

1. Check .gitignore (or .jjignore if it exists) for the workspace directory pattern
2. If NOT in .gitignore:
   • Immediately add it: echo "workspaces/" >> .gitignore (or .workspaces/)
   • Commit the change: jj describe -m "gitignore: Add workspaces directory"
   • This prevents accidentally tracking workspace contents

Never skip this verification - it's a critical safety check.

3. Workspace Creation

# Detect project name from git/jj repository
PROJECT_NAME=$(basename $(jj workspace root))

# Construct workspace path
WORKSPACE_PATH="<selected-directory>/${PROJECT_NAME}-<branch-or-feature-name>"

# Create the workspace
jj workspace add "$WORKSPACE_PATH"

# JJ will automatically:
# - Create the directory
# - Set up a new workspace tracking the current repository
# - Create a new working-copy commit

4. Project Setup (Auto-detect and run)

After workspace creation, detect project type and run appropriate setup:

Detection patterns:

• package.json → npm install or yarn install or pnpm install
• Cargo.toml → cargo build
• pyproject.toml → poetry install or pip install -e .
• flake.nix → nix develop or hey shell
• Gemfile → bundle install
• go.mod → go mod download

Always:

1. Change to workspace directory: cd "$WORKSPACE_PATH"
2. Run the appropriate setup command
3. Report any setup errors to the user

5. Baseline Verification

Before reporting success, run project tests to ensure clean state:

# Attempt to run tests based on project type
# Examples:
npm test
cargo test
pytest
nix flake check
# etc.

If baseline tests fail:

• Report the failure to the user
• Do NOT proceed with implementation unless user explicitly approves
• The workspace may have inherited an unstable state

6. Report Status

Provide a clear summary:

✓ JJ workspace created at: <path>
✓ Project setup completed: <command run>
✓ Baseline tests: <passed/failed>
✓ Ready to work on: <feature/branch name>

To switch to this workspace:
  cd <workspace-path>

To return to main workspace:
  cd <original-path>

To list all workspaces:
  jj workspace list

JJ Workspace Commands Reference

# Create new workspace
jj workspace add <path>

# List all workspaces
jj workspace list

# Remove a workspace (doesn't delete files)
jj workspace forget <workspace-name>

# Show workspace root
jj workspace root

# Update workspace to latest changes
jj workspace update-stale

Critical Rules

1. Never skip .gitignore verification for project-local workspace directories
2. Always follow the directory priority system - don't assume location
3. Require explicit permission before proceeding if baseline tests fail
4. Report clearly when workspace is ready with all relevant paths and commands
5. Auto-detect and run setup - don't make the user do it manually

JJ-Specific Considerations

Unlike git worktrees, jj workspaces:

• Share the same operation log (visible in jj op log)
• Each workspace has its own working-copy commit
• Changes in one workspace don't affect others until explicitly moved/rebased
• No need to specify a branch - jj creates a new working-copy commit automatically
• Use @ to refer to the current workspace's working-copy commit

Integration Notes

This skill is typically invoked during:

• Feature development requiring isolation from main work
• Testing changes without affecting current workspace
• Parallel development on multiple features
• Experimentation that might be abandoned

Pairs well with:

• JJ squash workflow for finishing work
• JJ split for organizing changes before moving back to main workspace