Hello! I'm having approximately the same error as ...

# ksp

[Daniel Pejcinovski]

Hello!
I'm having approximately the same error as the following post on StackOverflow:
https://stackoverflow.com/questions/79311813/kotlin-ksp-how-to-generate-aggregating-output-files

I'm trying to, in a symbol processor, get every class implementing a specific interface, create a single new file and to it add a line for each class implementing that interface.
I open the file once during processing, passing containingFile for every KSClassDeclaration I find that matches my criterion, and setting the aggregating flag to true.
I also wrap each KSClassDeclaration in a KSTopDownVisitor to write my data.

As far as I understand KSP, this should be everything necessary to not reprocess the classes in future runs, but I can see that it runs multiple times and as soon as it does it causes a fileAlreadExistsException.

Any ideas?

[David Rawson]

That Stack Overflow question is very hard to parse, but a common cause of FileAlreadyExistsException is attempting to write the file even when there are no relevant symbols found.

The pseudocode for a simple processor doing what you described should be something like:

1. Get all classes implementing a specific interface
2. Process these classes somehow into a single collection of data for output
3. Only in the case where is data from step 2, write the file once based on the collection
There are solutions for more advanced use cases if you search the chat for FileAlreadyExistsException including writing in finish() and generating dummy outputs.

[jamireh]

We ran into https://github.com/google/ksp/issues/1993 while developing our processors and implemented the provided workaround to get around this issue. It's not a catch all & could be another issue in your code (as David has pointed out) but give it a try?

[Daniel Pejcinovski]

Sorry for the late reply, but for posterity and other users I managed to implement what David suggested and it works perfectly.