Improve error message for broken CSS in CachedStaticFilesStorage
|Patch needs improvement:
When a CSS file references a non-existing image,
CachedStaticFilesStorage raises an exception — which is the right thing to do at this point (see #18958).
But the backtrace doesn't tell which file contains the error. As a consequence, when switching a large project to
CachedStaticFilesStorage, these errors are difficult to locate and fix.
To improve this situation, we could change the output to show the name of each file before processing it:
Processing file xxx… DONE Processing file xxx… FAIL
The goal is to make available all the information that could be useful for debugging, not to change the implementation of