Is there a way to programmatically set fold start and end without a lexer?

[asumbek]

The title says it all...

[orbitalquark]

You can, by manually setting buffer.fold_level (https://orbitalquark.github.io/textadept/api.html#buffer.fold_level), just like a lexer would.

Scintilla, the editing component Textadept uses, has more documentation on this field: https://scintilla.org/ScintillaDoc.html#SCI_SETFOLDLEVEL

A lexer returns a list of fold levels: https://github.com/orbitalquark/scintillua/blob/8070514fbcd14e117f289881994644497bc52e29/lexers/lexer.lua#L1337
Textadept uses those levels to assign to buffer.fold_level:

textadept/core/lexer.lua

Line 140 in f8da4d8

for line, level in pairs(folds) do buffer.fold_level[line] = level end

You could do something similar, but without a lexer.

However, you'll need to make sure that the buffer you're trying to change fold levels for does not have a lexer with a folder, or else it will overwrite your changes.

[asumbek]

Oh thanks, I was trying to make a module that use tree-sitter for syntax highlighting and other features.