feat: add syntax.refresh_from_string utility function

src/syntax.zig

@@ -111,6 +111,47 @@ pub fn refresh_from_buffer(self: *Self, buffer: anytype, metrics: anytype) !void
     self.tree = try self.parser.parse(old_tree, input);
 }
 
+pub fn refresh_from_string(self: *Self, content: [:0]const u8) !void {
+    const old_tree = self.tree;
+    defer if (old_tree) |tree| tree.destroy();
+
+    const State = struct {
+        content: @TypeOf(content),
+    };
+    var state: State = .{
+        .content = content,
+    };
+
+    const input: Input = .{
+        .payload = &state,
+        .read = struct {
+            fn read(payload: ?*anyopaque, _: u32, position: treez.Point, bytes_read: *u32) callconv(.C) [*:0]const u8 {
+                bytes_read.* = 0;
+                const ctx: *State = @ptrCast(@alignCast(payload orelse return ""));
+                const pos = (find_line_begin(ctx.content, position.row) orelse return "") + position.column;
+                if (pos >= ctx.content.len) return "";
+                bytes_read.* = @intCast(ctx.content.len - pos);
+                return ctx.content[pos..].ptr;
+            }
+        }.read,
+        .encoding = .utf_8,
+    };
+    self.tree = try self.parser.parse(old_tree, input);
+}
+
+fn find_line_begin(s: []const u8, line: usize) ?usize {
+    var idx: usize = 0;
+    var at_line: usize = 0;
+    while (idx < s.len) {
+        if (at_line == line)
+            return idx;
+        if (s[idx] == '\n')
+            at_line += 1;
+        idx += 1;
+    }
+    return null;
+}
+
 fn CallBack(comptime T: type) type {
     return fn (ctx: T, sel: Range, scope: []const u8, id: u32, capture_idx: usize, node: *const Node) error{Stop}!void;
 }