The French Socialist Party has always supported and continues to support conscription. Chirac dropped it in 2001, and Hollande, the first Socialist since then, has reintroduced quasi-conscription in the way of something similar to National Citizen Service in the UK. (uncoincidentally, Chirac has had his majority in Parliament vanished away since a large faction of his party stopped supporting him, and the socialists formed a government, effectively making France a nation without lawmaking for years)
Hamon wants a full-scale reintroduction.
It's part of French culture to be sent away to be disciplined anyway, to start the process of entering adulthood symbolically. You won't find a party, left or right, that opposes it. Maybe Greens, but even they haven't announced their policy regarding this.