Custom Shrinking Support via `treesitter`

[Boarders]

I am not sure if this is possible or useful, but I wanted to discuss if it makes sense to add custom shrinking for any language with a treesitter grammar, so at minimum if a language doesn't have more sophisticated support one could fall back to this. I am not entirely sure how this would work, but would be interested to try to implement it after discussing here.

[DRMacIver]

So I'd very happily accept a pull request for this if you can make it work, and am happy to provide thoughts on making it work, but I have looked into this briefly in the past and found treesitter a little unpromising for this. I suspect treesitter grammars are probably more useful as the basis for developing specific reduction passes than they are as a fully generic drop-in mechanism.

The reason is that AFAICT, treesitter doesn't provide quite enough information or capabilities for making modifications to the generated tree - it's a parser only, with no generator, and it's not at all straightforward to find from it what a good replacement node is in a given context. This makes the main thing you can do with it be suggesting deletions, and shrinkray is already pretty good at pure deletion strategies.

I think there's probably still some useful capability to be developed here - for example, you could keep track of strings you've seen for each node type, and try them as substitutions - but I didn't convince myself that it was worth the effort of investigation.

All this being said, I'd be delighted to be wrong, and if you'd like to give it a go I'd be very happy to provide feedback. I'd suggest that it would be worth starting with finding some test cases in languages with treesitter grammars that shrinkray currently doesn't reduce well, and seeing how a treesitter could help you if starting from shrinkray's final shrunk target.