(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.
(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.