index out of bounds bug

[raisinrand]

hi, there is a bug when parsing this template in non-comptime mode
{{#a}} {{#b}}{{/b}}{{/a}}

this panics when rendering:

thread 148525 panic: index out of bounds: index 3, len 2
/home/randy/.cache/zig/p/1220897a76b954e9811b760ba8e465d6c2c41ad3f69c8ce30c708e24af8ff12cb182/src/rendering/rendering.zig:1189:62: 0x10a2b0a in levelCapacityHint (codegen)
                            const section_children = elements[index .. index + section.children_count];
                                                             ^
/home/randy/.cache/zig/p/1220897a76b954e9811b760ba8e465d6c2c41ad3f69c8ce30c708e24af8ff12cb182/src/rendering/rendering.zig:804:69: 0x10a26fa in render (codegen)
                        const capacity_hint = self.levelCapacityHint(elements);
                                                                    ^
/home/randy/.cache/zig/p/1220897a76b954e9811b760ba8e465d6c2c41ad3f69c8ce30c708e24af8ff12cb182/src/rendering/rendering.zig:1375:35: 0x10a6758 in bufRender__anon_9310 (codegen)
            try data_render.render(template.elements);
                                  ^
/home/randy/.cache/zig/p/1220897a76b954e9811b760ba8e465d6c2c41ad3f69c8ce30c708e24af8ff12cb182/src/rendering/rendering.zig:655:31: 0x10a68d6 in internalAllocRender__anon_9309 (codegen)
    try RenderEngine.bufRender(list.writer(), template, data, PartialsMap.init(partials));
                              ^
/home/randy/.cache/zig/p/1220897a76b954e9811b760ba8e465d6c2c41ad3f69c8ce30c708e24af8ff12cb182/src/rendering/rendering.zig:148:35: 0x107144c in allocRenderPartialsWithOptions__anon_5943 (codegen)
    return try internalAllocRender(allocator, template, partials, data, render_options, null);
                                  ^
/home/randy/.cache/zig/p/1220897a76b954e9811b760ba8e465d6c2c41ad3f69c8ce30c708e24af8ff12cb182/src/rendering/rendering.zig:108:46: 0x106151c in allocRender__anon_5440 (codegen)
    return try allocRenderPartialsWithOptions(allocator, template, {}, data, .{});
                                             ^

it looks like this happens because in parser.zig we omit empty nodes in produceNodes, but if this occurs in a section, we don't update the children_count for the section
the space in the template is empty after trimming whitespace

for (nodes.items) |*node| {
    if (!node.text_part.isEmpty()) {
        list.appendAssumeCapacity(try self.createElement(node));
    }
}

i think an easy fix is to just get rid of this check, unless it's necessary for some reason?

[batiati]

Hey, @raisinrand, can you write a unit test to reproduce it?
I tried this one, but it passed:

            test "Sections: Empty nodes" {
                const template_text = "{{#section}}A{{#empty}}{{/empty}}{{/section}}";
                const expected = "A";

                const Data = struct { section: bool, empty: bool };
                const data = Data{ .section = true, .empty = false };
                try expectRender(template_text, &data, expected);
            }

IIRC, empty nodes are omitted mostly because of the streamed render. To fix this bug we could just check section.children_count == 0.

[raisinrand]

ah, the bug happens if there is a whitespace-only text node in a section, not if there is an empty section

            test "Sections: Empty node in section" {
                const template_text = "{{#section}} {{node}}{{/section}}";
                const expected = "";

                const Data = struct { section: bool, node: bool };
                const data = Data{ .section = true, .node = false };
                try expectRender(template_text, &data, expected);
            }

this version fails