anonymous function as a statement crashes compiler

[getkey]

Describe the bug
When an anonymous function is created without being assigned, just as a single statement, it crashes the compiler.

() => {}; // like this
function() {}; // or that

This issue appeared in 3.18.2.

Logs

Stack trace

[!] (plugin svelte) TypeError: Cannot read property 'type' of undefined
src/templates/SettingsPopup.svelte
TypeError: Cannot read property 'type' of undefined
    at ExpressionStatement (/mnt/data/devel/xplozzle/node_modules/svelte/node_modules/code-red/dist/code-red.mjs:340:48)
    at handle (/mnt/data/devel/xplozzle/node_modules/svelte/node_modules/code-red/dist/code-red.mjs:70:17)
    at nodes.map.statement (/mnt/data/devel/xplozzle/node_modules/svelte/node_modules/code-red/dist/code-red.mjs:248:18)
    at Array.map (<anonymous>)
    at handle_body (/mnt/data/devel/xplozzle/node_modules/svelte/node_modules/code-red/dist/code-red.mjs:247:21)
    at handlers.BlockStatement.scoped (/mnt/data/devel/xplozzle/node_modules/svelte/node_modules/code-red/dist/code-red.mjs:324:7)
    at /mnt/data/devel/xplozzle/node_modules/svelte/node_modules/code-red/dist/code-red.mjs:226:10
    at handle (/mnt/data/devel/xplozzle/node_modules/svelte/node_modules/code-red/dist/code-red.mjs:70:17)
    at handlers.ArrowFunctionExpression.scoped (/mnt/data/devel/xplozzle/node_modules/svelte/node_modules/code-red/dist/code-red.mjs:837:19)
    at /mnt/data/devel/xplozzle/node_modules/svelte/node_modules/code-red/dist/code-red.mjs:226:10

To Reproduce
https://svelte.dev/repl/574ed4913495492bb1c9580e1b203de8?version=3.20.1

Expected behavior
This useless function must be created but since it's not called, nothing special should happen.

Severity
Honestly it's not very severe. I noticed this issue because I mistakenly forgot to return my anonymous function. I don't really see any reason anyone would want to create an anonymous function and never call it.

However, it's valid JavaScript so it should either be supported or fail with a more explanatory error: "You are making an anonymous function and never calling it. Are you really sure?". But I would argue this is a linter's job, not svelte.
So I think svelte should just support it.

[arxpoetica]

I can confirm this is broken. It appears the breaking change happened between v3.18.1 and v3.18.2:

• Working: https://svelte.dev/repl/574ed4913495492bb1c9580e1b203de8?version=3.18.1
• Broken: https://svelte.dev/repl/574ed4913495492bb1c9580e1b203de8?version=3.18.2

That should help narrow down what happened between the two versions.

Version compare for ease: 46634e8...c323282

[matthewtole]

I've been looking into this, and I've tracked down the cause to #4385 which upgraded the version of https://github.com/Rich-Harris/code-red.

I believe the crash is happening in code-red, and specifically this commit is what caused it: Rich-Harris/code-red@2ad7c7a

I don't understand enough about code-red works to fix it, but hoping that this information will help someone else out.

[Conduitry]

Yup, looks like a code-red issue. I've opened Rich-Harris/code-red#38

[Conduitry]

This is fixed now in 3.23.2 - https://svelte.dev/repl/574ed4913495492bb1c9580e1b203de8?version=3.23.2