TL;DR

The event-function module has a create_bucket input argument that should also be supported by this module.
The inclusion of this input argument permits the use case of using a bucket that already exists for the storage of function deployment sources when create_bucket is false and bucket_name points to an existing bucket.

Terraform Resources

https://registry.terraform.io/modules/terraform-google-modules/event-function/google/latest?tab=inputs

Detailed design

In main.tf:

module "main" {
    ...
    create_bucket = var.function_create_bucket
    ...
}

In variables.tf:

variable "function_create_bucket" {
    type = bool
    default = true
    description = "Whether to create a new bucket or use an existing one. If false, `bucket_name` should reference the name of the alternate bucket to use."
}

Additional information

I am more than happy to create a PR for this, and I think this should be supported since finer control is always nice, especially since that finer control is already supported by the underlying event functions module this module makes use of.