Svelte 5: unnecessary $.proxy() generated for += assignment

[jeremy-deutsch]

Describe the bug

When the Svelte 5 compiler sees a +=, it generates code like the following:

In this case, $.proxy() will always just return the value it’s passed, since it’s impossible for an addition expression in JS to return a non-primitive value. The compiler should probably just not wrap the expression in $.proxy() (though I get that the overhead and additional code size here is minor).

Reproduction

https://svelte-5-preview.vercel.app/#H4sIAAAAAAAAE0WOwQrCMBBEfyUEDy0K6jW2gt9hPNR0C8F0E5KNICH_bpKCHmdm3-wkvmgDgYt74jitwAW_OccPnD6uivAGQ1B0sNGr6gxBee3oKlGSAWLKRiQ2sl2giaA79ZeSlGyJqEhbZBqVhxWQup6lmkjamP3IzvWYssTh-K_F4RmJCmlRGa1eY_pV5Pa2uUGw1HoavRHXMnS1s140zFyQj5Af-QvG9JrM4wAAAA==

Logs

No response

System Info

Svelte v5.0.0-next.26 (in Svelte 5 playground)

Severity

annoyance

[jeremy-deutsch]

Actually, looking at the code, should_proxy probably shouldn't be proxying any BinaryExpressions, since they all evaluate to primitive values.