Undeclared variable with MRV/tuple function composition

[Rob Schluntz]

When calling a function taking multiple tuple arguments using a function argument returning multiple values, codegen puts a temporary in the wrong place. E.g.,

[int, int] bar() { return [3, 4]; }
[void] foo([int] x, [int] y) {}

int main() {
  foo(bar());
}

The _unq_finished variable is inserted into the statement expression generated as part of the tuple constructor for x, but needs to be accessible in y's constructor as well.