-----
public void hash (T) (scope const auto ref T record) // @safe  // uncomment to compile
    if (is(T == struct))
{
    foreach (const ref field; record.tupleof)
    {
        hash(field);
    }
}

public void hash (T) (scope const auto ref T[] records) @safe
{
    foreach (ref record; records)
        hash(record);
}

@safe void main ()
{
    struct Foo
    {
        Foo[] foo;
    }

    Foo foo;
    hash(foo);
}
-----

$ dmd test.d
$ test.d(15): Error: @safe function test.hash!(Foo).hash cannot call @system function test.hash!(Foo).hash
$ test.d(3):        test.hash!(Foo).hash is declared here

Uncommenting '@safe' makes it compile. The safety should have been inferred.