I've found the C'est la Grève site (in French only) to be pretty helpful for basic strike info in the past:
Liste des grèves en cours et à venir en France ? Cestlagreve .
I was planning two weeks in France in late April. I pre-booked hotels (all refundable) a while back to get good prices, and now I see that 3 of my 4 planned train trips fall on strike days. And they're on TER, too, so not reservable and likely to be jammed if I switch days. This was supposed to be a nice, easy relaxing trip, and I'm not super-invested in taking it. So I'm seriously thinking it's not worth the inconvenience.