Attempting to bind values to reserved name should trigger a warning

[ogoffart]

Discussed in #738

^{Originally posted by hbina December 11, 2021}
I have wasted a disgusting amount of time only to realize that row is a reserved keyword. I basically had something like this compiled without warning, which does not even make any sense because row here is shadowed by the reserved name anyways.

for row in bson.inner : HorizontalBox {
    key := Text {
        text: row.key;
    }
    value := Text {
        text: row.value;
    }
}
```</div>

[ogoffart]

This is actually valid, and we use that quite a lot in our own code:

for x in foobar : Text { text: x; }
// or
for item in foobar : SomeStuff { item:item; }

The problem in the original example is that key and value element are not direct child.

Eventually we should change the lookup rules: #273

[ogoffart]

Lookup changes are done with the new syntax.
Closing this issue now.