Meaningless "Unknown identifier" error in list assignment

[vtereshkov]

fn foo(): (int, bool) {
    return 42, true
}

fn main() {
    a := 9
    b := [2]int{5, 7}
    
    //a, flag := foo()    // OK
    b[0], flag := foo()    // Unknown identifier flag
    
    printf("%v %v %v\n", a, b, flag)
}

[vtereshkov]

Go says "non-name b[0] on left side of :=".