Builder silently drops custom sections

[osa1]

Repro:

use parity_wasm::elements::Section;

fn main() {
    let path = std::env::args().nth(1).unwrap();
    let module = parity_wasm::deserialize_file(&path).unwrap();
    let module_old = module.clone().into_sections();
    let mbuilder = parity_wasm::builder::from_module(module);
    let module_new = mbuilder.build().into_sections();
    println!(
        "old sections: {:?}",
        module_old.iter().map(section_name).collect::<Vec<_>>()
    );
    println!(
        "new sections: {:?}",
        module_new.iter().map(section_name).collect::<Vec<_>>()
    );
}

fn section_name(section: &Section) -> &'static str {
    match section {
        Section::Unparsed { .. } => "unparsed",
        Section::Custom(_) => "custom",
        Section::Type(_) => "type",
        Section::Import(_) => "import",
        Section::Function(_) => "function",
        Section::Table(_) => "table",
        Section::Memory(_) => "memory",
        Section::Global(_) => "global",
        Section::Export(_) => "export",
        Section::Start(_) => "start",
        Section::Element(_) => "element",
        Section::DataCount(_) => "datacount",
        Section::Code(_) => "code",
        Section::Data(_) => "data",
        Section::Name(_) => "name",
        Section::Reloc(_) => "reloc",
    }
}

If I pass this a .wasm file with custom sections I see an output like:

old sections: ["type", "import", "function", "table", "memory", "global", "export", "element", "code", "data", "custom", "custom", "custom", "custom", "custom", "custom", "custom", "custom", "custom", "custom"]
new sections: ["type", "import", "function", "table", "memory", "global", "export", "element", "code", "data"]

So builder drops the custom sections. This is quite unexpected to me, and it's also not documented. Other sections are preserved, I'm not sure why custom sections are dropped.

[chevdor]

Hello @osa1, thanks for reporting this issue. Could you please check if you still run into this issue with your wasm?

I ran a test and the custom section was preserved. I think this might have been fixed in #300