This comes up in one or more of the Civilized Nations every few years. It would accomplish nothing except to end the Confessional. Who is going to confess to a priest who is required to tell the government? You get a law like this in the technological present and a requirement for recording of everything in a confessional will come shortly. If a priest “obeys” such a law even if passed and enforced, he will have his faculties as a priest stripped from him.
In my opinion, that's the whole point of this silly idea. The people who push this stuff aren't really trying to get "more justice". They are just trying to weaken the Catholic Church by making people avoid one of the sacraments.
I say that, and I'm not Catholic. But I see "do-gooders" trying to dilute a very old religious practice and it bothers me, even if it isn't my religious practice.
And that's the point. The Total State resents and cannot abide any authority (moral or otherwise) it does not directly control. Thus, the Total State must destroy the family, civic organizations, and religious institutions. We saw this mentality in its full flower in National Socialist Germany, the Union of Soviet Socialist Republics, and the Peoples' Republic of China. For example. We also see it in the various Islamic States.
And we're increasingly seeing it in the increasingly misnamed "Free World".
If they were to pass a law that required clergy to report crimes reported to them in confession I could see sociopaths making a game out of confessing crimes (real and fictional) just to make the priest squirm between the requirements of the civil laws and excommunication. If the “penitent” gets caught for a crime he turns the priest in saying “I confessed all this to Fr. So-and-so” and take satisfaction in seeing the priest go through legal hell. Another could go from church to church confessing fictional crimes and if one of them breaks (probably after seeing a few episodes of their brethren raked over legal coals) and reports it to the police the false penitent gets the satisfaction of outing a hypocrite and when investigated there is no evidence other that the hearsay of the priest. It is a catch 22 for the church and of little value to the authorities.
There is nothing the devil wants more than to get us to compromise with the world because every little compromise takes us further from God.