[Issue 24636] New: Closures need to capture the whole frame

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24636

          Issue ID: 24636
           Summary: Closures need to capture the whole frame
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: qs.il.paperinik at gmail.com

```d
// Use -dip1000
int delegate() @safe f(bool fail)(int x) @safe
{
    int* p = &x;
    static if (fail)
        return () => *p;
    else
        return () { cast(void) x; return *p; };
}

void main() @safe
{
    auto dg = f!false(42);
    assert(dg() == 42);
}
```

If a variable isn’t expressly named in a closure, it is not captured.
When `f` returns, `p` points to `x`, but `x` is not part of the capture and
therefore gone when it’s not mentioned itself.

The compiler, unless it can prove that for some of the local state, it cannot
possibly be referenced by a delegate, must put the whole stack frame into the
closure.

This seems similar to https://issues.dlang.org/show_bug.cgi?id=20956, but it
requires nothing but being able to take the address of `x`.

--