loom diff

Show the changes a module run would produce.

loom diff [path] [flags]

loom diff has two fidelity levels.

• Full (default): runs the module in local mode — clones each target, executes every operation (including pure: true shell commands), commits locally, and skips push and PR creation — then prints a git diff of each target against its base branch. Because operations actually run, this is the complete change a run would make, including files rewritten by shell commands (formatters, codegen).
• Quick (--quick): simulates the run (dry-run). It prints unified diffs for newFiles and patch operations only and executes nothing — fast and side-effect-free, but it cannot show changes made by shell commands.

Flags

Flag	Description
--quick	Simulate the run (dry-run); show newFiles/patch diffs only, execute nothing
--partial	When the run fails, still print the diff of changes made before the error (below a warning)
-p, --param key=value	Set a parameter (repeatable)
--params-file file.yaml	Load parameters from a YAML file
--target-path /path	Keep target clones here for inspection instead of a cleaned-up temp dir
--author name	Default git author name for commitPush
--email email	Default git author email for commitPush
-v, --verbose	Enable debug logging
--log-level level	Set log level: debug, info, warn, error
--log-format format	Set log format: pretty (default), text, json

The [path] argument accepts the same forms as loom run: a local directory or a git URL (with an optional //subdir).

Examples

Full diff

The complete change, including shell-op effects:

loom diff ./onboard-service -p serviceName=payments

Each target is cloned into a temporary directory that is removed once the diff is printed. Pass --target-path to keep the numbered clones for inspection:

loom diff ./onboard-service -p serviceName=payments --target-path ./preview

Quick diff

A fast, no-execution preview of newFiles/patch changes:

loom diff ./onboard-service -p serviceName=payments --quick

Failures

When the run fails, loom diff prints the error right after the failing module's logs and exits non-zero — no diff is printed, so the error is not buried beneath it. To still inspect the changes made before the failure, add --partial; the partial diff is printed after the error, beneath a warning marking it incomplete:

loom diff ./onboard-service -p serviceName=payments --partial

TIP

Use full mode when your module has shell operations that rewrite files (formatters, linters, codegen) — quick mode never runs them, so their effects are invisible to it. Use --quick when you only need to preview templated files and patches and want to avoid executing anything.