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I don't know all the internals and features of tree-sitter, but I wonder if it could be used to create a paredit or smartparens mode which would work on all languages and respect their semantic. Ideally it wouldn't even have to be emacs specific.
It is kind of already happening in emacs thanks to the SMIE parser. Many of the sexp manipulation function are working on my ocaml code in a meaningful way because the mode for ocaml is using SMIE. And some other tools such as paren-mode are taking advantage of the ocaml mode being based on SMIE too. It can properly detect that `begin` and `end` are equivalent to `(` and `)`.
Unfortunately, paredit and smartparens are not based on SMIE. So they kind of work on ocaml code. But not really. If they were based on a single tool that knows correctly the syntax (and maybe some semantic) of all the languages parsed, they could be much more reliable. And even do more powerful operations.