It's really hard! :) (1) Parsing an arbitrary language is hard. Without tree-sitter, difftastic would probably be a lisp-only tool. You also want a parser that

It's really hard! :) (1) Parsing an arbitrary language is hard. Without tree-sitter, difftastic would probably be a lisp-only tool. You also want a parser that preserves comments. (2) Inputs may not be syntactically well formed. (3) Efficiently comparing trees is extremely difficult (difftastic is O(N^2) in time and memory). (4) Displaying tree diffs is equally difficult. Alignment is particularly challenging when your 'unchanged before' and 'unchanged after' are syntactically the same, but textually different.