Problem:
Treesitter highlighter's on_line was iterating all the parsed trees,
which can be quite a lot when injection is used. This may slow down
scrolling and cursor movement in big files with many comment injections
(e.g., lsp/_meta/protocol.lua).
Solution:
In on_win, collect trees inside the visible range, and use them in
on_line.
NOTE:
This optimization depends on the correctness of on_win's botline_guess
parameter (i.e., it's always greater than or equal to the line numbers
passed to on_line). The documentation does not guarantee this, but I
have never noticed a problem so far.
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