When looking for an external snippet, if it cannot be found, the diagnostic is a basic "File not found" message.

It would be more informative if it said something like:

File not found on source path or snippet path.

The use of "source path" is deliberate, as compared to any specific option, because it may be the package-oriented source path or the module source path, and even the source path can be set in various ways (--source-path, -sourcepath, -classpath, etc) But the term should be enough to indicate that some path setting is required.