unexpected token error for "export let value = getContext('value') || (v) => v;"

[hamilton]

Describe the bug

I am updating a large Svelte codebase from 3.12.1 to 3.18.1, and received a parsing error for the following line that previously worked fine:

export let value = getContext('value') || (v) => v;

If I replace the arrow function with something like function myFunction(v) { return v} the error goes away.

To Reproduce

https://svelte.dev/repl/60c49c4243014a69acfc47b79437ae7e?version=3.18.1 reproduces the issue minimally.

Expected behavior
The pattern export let myFunc = getContext('myFunc') || (v) => v; should not cause any kind of error.

Stacktraces
If you have a stack trace to include, we recommend putting inside a <details> block for the sake of the thread's readability:

Stack trace

Error: Unexpected token (Note that you need plugins to import files that are not JavaScript)
13: export let tickFormatter = getContext('tickFormatter') || ((v) => v);

Information about your Svelte project:

• Your browser and the version: Firefox 73.0b9 (64-bit)

• Your operating system: OS X 10.14

• Svelte version 3.18.1

• Whether your project uses Webpack or Rollup

Severity

This is not blocking my team at the moment, since we have a workaround by using function myFunction(v) { return v }; in place of the arrow function but I could see this throwing others off and eroding trust in Svelte.

[Conduitry]

Opened Rich-Harris/code-red#31 for underlying code generation issue.

[Conduitry]

This is fixed in 3.18.2 - https://svelte.dev/repl/60c49c4243014a69acfc47b79437ae7e?version=3.18.2