U2 and Martin Garrix light up the summer with “Fireflies”

U2 and Martin Garrix have released “Fireflies,” completing a collaboration that began six summers ago and grew into a full-band recording. U2's official site says Garrix debuted the track at Tomorrowland with The Edge joining him onstage. The finished song brings Bono, The Edge, Adam Clayton and Larry Mullen Jr. into Garrix's electronic world, balancing festival-scale lift with the reflective atmosphere suggested by its title. The long gestation makes the release more than a quick crossover. It is another example of U2 testing its songs in unfamiliar settings — and of a younger producer meeting the band as collaborators rather than as a sample from rock history.