Print a warning when replace matches the empty String
Print a warning when replace matches the empty String

This pattern is unlikely to be intentional (and likely to OOM), but is sometimes used; if the change is NOOP it's harmless.

Also add more verbose logging.

PiperOrigin-RevId: 313502966
Change-Id: I265cedc6ebde78eec3db3dda75533af5778eda7a

google/copybara,google/copybara,google/copybara