KERRIA japonica "Pleniflora".

Commonly known as a Japanese rose or Jews mallow. Kerria japonica

Hi I would keep an eye on it, it can sucker quite a lot and can be hard to get rid of, not that you may want to, but I do cut mine back, mine is underneath another shrub been in many years so I usually chop back the bits I can see after flowering.

I agree on the id, it is a nice shrub but as Daylily says it can sucker but I fins it a pleasant colour at this time of year.

welcome to GoY too :o)

Kerria Japonica (sometimes called Batchelor's Buttons). No idea why it's been planted against a trellis, though, as it isn't a climber.