Very slow compilation using boot 2.5.2

Boot just auto updated to 2.5.2 and now compilation is very slow, more than 12 seconds for the demos/petrol examples for instance.

Start by reproducing the compilation slowdown with Boot 2.5.2 using the demos/petrol example mentioned in the issue, and compare it with the preceding Boot version. The payload names no source files or tests, so trace the compilation path and establish a measured regression before determining what counts as fixed.

Written by the indexing model from the issue text.