Use local directory for wrapper in Snakemake rule

I want to know how to use a local directory for wrapper in Snakemake rule.

I have read this Use Github URL for wrapper in Snakemake rule and try follows command

rule index:
    wrapper:
        "/public/home/bio/index"

But, I get a stderr with 'NoneType' object has no attribute 'name'.

Any help is much appreciated. Thanks.

Answer

It is (slightly hidden) mentioned in the docs.

For an absolute path:

rule index:
    wrapper:
        "file://public/home/bio/index"

Or for a relative path:

rule index:
    wrapper:
        "file:public/home/bio/index"