No one conscious of mortal sin should approach the Holy Eucharist, however contrite he may seem to himself
Now ecclesiastical usage declares that this examination is necessary, that no one conscious of mortal sin, however contrite he may seem to himself, should approach the Holy Eucharist without a previous sacramental confession. This, the holy Synod has decreed, is always to be observed by all Christians, even by those priests on whom by their office it may be incumbent to celebrate, provided the recourses of a confessor be not lacking to them. But if in an urgent necessity a priest should celebrate without previous confession, let him confess as soon as possible [see n. 1138 ff.]. (Denzinger-Hünermann 1647. Council of Trent, Session XIII, October 11, 1551)
Whoever publicly asserts that one may receive communion in mortal sin is excommunicated

If anyone says that faith alone is sufficient preparation for receiving the sacrament of the most Holy Eucharist: let him be anathema. And that so great a Sacrament may not be unworthily received, and therefore unto death and condemnation, this holy Council ordains and declares that sacramental confession must necessarily be made beforehand by those whose conscience is burdened by mortal sin, however contrite they may consider themselves. If anyone moreover teaches the contrary or preaches or obstinately asserts, or even publicly by disputation shall presume to defend the contrary, by that fact itself he is excommunicated. (Denzinger-Hünermann 1661. Julius III, Council of Trent, Session XIV, October 11, 1551)