Function parse_modern_root_incremental 

pub fn parse_modern_root_incremental(
    source: &str,
    old_source: &str,
    old_root: &Root,
    old_cst: &Document<'_>,
    edit: CstEdit,
) -> Result<Root, CompileError>

Parse a Svelte component into the modern AST root incrementally, reusing unchanged subtrees from a previous parse. Requires a previous CST document and the CST edit that was applied so tree-sitter can compute changed ranges.

Falls back to a full parse if the CST reports an error root.