How to modify Anns / How to use addAnnotationsForPretty properly?

[kahlil29]

I'm using ghc-exactprint to modify some source code.
I parse a haskell module using parseModuleFromString and obtain (Anns, ParsedSource)

Then I modify that ParsedSource and obtain a new ParsedSource.
I tried using addAnnotationsForPretty in the following manner:

Right (oldAnns, parsedSrc) -> do
      let newSrc = someModificationFunction parsedSrc
      let newAnns = addAnnotationsForPretty [] newSrc oldAnns
      pure $ exactPrint newSrc newAnns

When I do this, the file is printed without language extensions and formatting is lost (I'm guessing that since the modified annotations don't match with the new ParsedSource, the annotations are being discarded/not being modified as expected by addAnnotationsForPretty.

What is the best way to modify the existing annotations in order for them to match up/make sense/accomodate for the changes in the ParsedSource ?

[ocharles]

If you have parsed source code you don't need to use addAnnotationsForPretty - the annotations you have are already sufficient. You should just modify the annotations you got from parsing. If you share some source code, we can help more.