`#each` blocks without an item + key expression cause a runtime error

[x0k]

Describe the bug

When using an #each block like this: {#each { length: data.length }, index (data[index])}, the generated JavaScript is invalid — (, index) => data[index], which results in a runtime error.

Expected: this syntax should either be supported or produce a compile-time error.

Workaround: {#each { length: data.length } as _, index (data[index])}

Reproduction

REPL

Logs

System Info

-

Severity

annoyance

[x0k]

#16966