WARSAW—Poland’s highest court ruled on Thursday that some parts of EU treaties are incompatible with the Polish constitution, challenging a pillar of European integration and sharply escalating a dispute between Brussels and Warsaw. The European Commission said the ruling raised serious concerns about the primacy of EU law, setting it on a full collision course with Poland’s nationalist rulers after years of legal and political wrangling. Poland’s Law and Justice (PiS) party government is embroiled in a battle of values with Brussels, focused on disputes over the independence of courts, media freedoms, LGBT rights, and other issues. Critics say that by going further and challenging the supremacy of EU law, the PiS government not only jeopardizes Poland’s long-term future in the 27-nation bloc but also the stability of the EU itself. PiS denies this and says it has no plans for a “Polexit.” Poland’s Constitutional Tribunal took on the case …