Add default annotations for pretty printing about ghc-exactprint HOT 3 CLOSED

I'd be willing to take a crack at this if you can provide some pointers on where to start. I was just looking at printStringAtMaybeAnnThen, but it appears that's too late in the pipeline.

from ghc-exactprint.

I think in the Language.Haskell.GHC.ExactPrint.Print module would need modification so that if it looks up an annotation and it is not there it uses an alternate default version.

The problem is that a lot of annotations are optional as a given datatype can appear in multiple roles in the AST, so simply doing a default on every possible annotation via a separate lookup would not work. There would have to be a degree of context awareness.

So running a separate pass on the unannotated AST to add the appropriate defaults might be a simpler process, which would then be another interpreter over AnnotationF, doing something similar to the Delta one but using built-in knowledge to use defaults.

Or, as @mpickering suggested, the simplest might be to just use the GHC pretty-printer, and then parse it using ghc-exactprint to get a fully annotated AST which can be spliced into the original. Of course there is still an open ticket on GHC (https://ghc.haskell.org/trac/ghc/ticket/3384) to verify that the output of the GHC pretty-printer is in fact a faithful representation of the original. i.e. that parsing the pretty-printer output yields the same AST.

This is just an initial brain dump, sorry if it is a bit incoherent.

from ghc-exactprint.

This feature exists in current master, via addAnnotationsForPretty

from ghc-exactprint.