Incremental

What you'll learn

• Editor-style update: describe an edit, reparse, and diff the trees.

Complete example

examples/incremental_parse.zig:

var old_tree = try parser.parseString("1 + 2");
defer old_tree.deinit();

const edit = treesitter.InputEdit{
    .start_byte = 4,
    .old_end_byte = 5,
    .new_end_byte = 6,
    .start_point = .{ .row = 0, .column = 4 },
    .old_end_point = .{ .row = 0, .column = 5 },
    .new_end_point = .{ .row = 0, .column = 6 },
};
var new_tree = try parser.parse(&old_tree, edit, "1 + 22");
defer new_tree.deinit();

const ranges = try old_tree.getChangedRanges(&new_tree);
defer old_tree.freeChangedRanges(ranges);
for (ranges) |r| {
    std.debug.print("changed: bytes [{d}, {d}]\n", .{ r.start_byte, r.end_byte });
}

Running the example

zig build run-incremental_parse

Expected output

before: 1 + 2
after:  1 + 22
changed: bytes [4, 6]

Input

Original source 1 + 2.

Edit

Insert one byte at offset 4 (2 → 22): start 4, old end 5, new end 6, same row, columns adjusted.

Result

New tree for 1 + 22 with only bytes [4, 6] reported changed. The untouched 1 + prefix reuses old subtrees (parser.reused_node_count > 0).

API used

• Parser, InputEdit, Changed Ranges

Memory ownership

Both trees coexist; the old tree is only read during reuse. Each deinit frees its own pool.

Performance considerations

Trailing edits reuse large subtrees in single clones; leading-edge edits re-examine more. See Performance.

Related guides

• Incremental Parsing, Editing Trees