UPDATE:

Summary

This PR adds support for the --format=json flag to the uv sync --dry-run command. When enabled, the command outputs details in JSON format, making it easier to parse and integrate with other tools.

the dry run output json includes:

• Project directory.
• Environment path & action taken(Create/Update/None).
• Python executable path.
• Python version.
• Lockfile path & action.
• Packages (would install/download/remove).

The Json output is currently pretty-printed for readability.

Test Plan

Manual testing has been performed to verify JSON output.

--script

cargo run sync --dry-run --script foo.py --format=json
output:

{
  "project_dir": "/home/root/rust/uv/uv",
  "environment": {
    "path": "/home/root/.cache/uv/environments-v2/foo-bc19cb0acffe1e16",
    "action": "already_exist",
    "python_executable": "/home/root/.cache/uv/environments-v2/foo-bc19cb0acffe1e16/bin/python3",
    "python_version": "3.13.0"
  },
  "lockfile": null
}

--project

cargo run sync --dry-run --project test_dir --format=json
output:

{
  "project_dir": "/home/root/rust/uv/uv/test_dir",
  "environment": {
    "path": "/home/root/rust/uv/uv/test_dir/.venv",
    "action": "already_exist",
    "python_executable": "/home/root/rust/uv/uv/test_dir/.venv/bin/python3",
    "python_version": "3.13.0"
  },
  "lockfile": {
    "lockfile_path": "/home/root/rust/uv/uv/test_dir/uv.lock",
    "action": "create"
  }
}

Note: 2>/dev/null can be appended to the end of the command to redirect stderr away and show only the stdout(which contains the json only).
Related Issue
Resolves #12387.