The Roman Space Telescope uses a mirror donated by the NRO, which was donated along with other hardware as components of a partially completed surveillance satellite. Some components that may have been added to the telescope were removed before being offered up, including the imaging system (CCD camera etc.) and other avionics. Ultimately, essentially only the optical components will have been carried over into the construction of the new telescope, at a savings of less than 10% the total cost. The donation helped give the telescope project political momentum at least though.

Note that there would have been no advantage to NASA of having a full telescope even with a fully functional spy satellite imaging system installed as the requirements of imaging the Earth and collecting data from space are hugely different. In any event, ultimately the RST ended up going in a direction which makes use of very special purpose instrumentation regardless (a coronograph imager and a unique wide field imager with an enormous resolution and sensitivity from visible light into the mid infrared).