Add parallel steps

[amh4r]

Description

Add parallel steps using a new group.Parallel function. The new group package lives in an experimental directory, where it will remain until we feel it's stable.

func MyFn(ctx context.Context, input inngestgo.Input[any]) (any, error) {
	results := group.Parallel(
		ctx,
		func(ctx context.Context) (any, error) {
			return step.Run(ctx, "1a", func(ctx context.Context) (string, error) {
				return "1a output", nil
			})
		},
		func(ctx context.Context) (any, error) {
			return step.Run(ctx, "1b", func(ctx context.Context) (string, error) {
				return "1b output", nil
			})
		},
	)

	out := make([]string, len(results))
	for i, r := range results {
		if r.Error != nil {
			return nil, r.Error
		}
		out[i] = r.Value.(string)
	}
	return out, nil
}

[tonyhb]

Is this used as a waitgroup?

[amh4r]

It's effectively a waitgroup of 1. We want to run each step sequentially but also in a goroutine so that we can recover the control hijack

[jpwilliams]

Should we just repanic for now? I suppose this might be where we capture the non-Inngest panic and could return it as an error to Inngest in the future?

[amh4r]

Do you think we should recover the panic and repanic it outside the goroutine? I think that'll let our normal non-control-flow panic recovery logic work

[jpwilliams]

Ooh yeah if we already have something that captures panics then that'd be awesome.