svelte: Application won't compile - "cannot read property 'n' of undefined" since 3.16.1

• In continuation to what @antony said above, the issue is also caused by a carriage return of an empty component, like so:

<A>

</A>

The error goes away if you write <A></A>

This is what I meant by point #3 above. It’s not the sole cause though. You also need exactly 31 variable declarations.

I took the code from @dimfeld 's repro (thanks!) and took the List.svelte component out and started to trim it back.

This is as minimal as I can get it without making the error disappear:

https://svelte.dev/repl/909f45b7a2234ad2804d3dcecd59a54b?version=3.16.1

It seems to occur when you have exactly 31 variables declared and a component declaration.

Note:

• The component declaration is essential
• The number of variables is essential (31)
• The component must be declared with opening and closing tags on different lines

Here’s a reproduction: https://svelte.dev/repl/5357a38fcfc6441ebcf162fa5d307a12?version=3.16.1

This just imports the svelte-select library. I haven’t reduced this to a minimal test case, but hopefully it helps you figure this out. It appears to be failing on the file List.svelte inside svelte-select.

<script>
	import Select from 'svelte-select';
</script>

This script should try to compile all components in the project and allow the full stack trace and breakpoints using the built-in Node debugger.

Not sure if it needs tweaking for sapper though.

const svelte = require('svelte/compiler');
const fs     = require('fs');
const glob   = require('glob');

function do_compile(err,data) {
    if (err) {
        console.log("Couldn't read file:", err);
        process.exit(-1);
    }

    let result = svelte.compile(data);
}

function call_svelte(err, files) {
    if (err) {
        console.log("Glob error:", err);
        process.exit(-1);
    }

    files.forEach(f => {
        fs.readFile(f, {encoding:"utf8"}, do_compile);
    });
}

glob('src/*.svelte', call_svelte);
glob('src/**/*.svelte', call_svelte);