Fix Issue 20909 - .offsetof fails on forward reference of field

[BorisCarvajal]

Run semantic on the variable first to make sure it's an instance field.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20909	normal	.offsetof fails on forward reference of field

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "stable + dmd#11253"

[WalterBright]

The problem here is that sc is the context of the expression, which is not the same as the context of the field. The solution is to use null instead of sc.

[BorisCarvajal]

Absolutely, thanks.

[BorisCarvajal]

Done.

[BorisCarvajal]

Any more feedback on this little fix?

[ghost]

maybe try to surround with v.inuse++ and v.inuse--.

[BorisCarvajal]

Thanks for replying.
Do you have any recommendations on when to use the inuse variable?
For example in this file I can't find any use of them at dsymbolSemantic() calls.

[ghost]

It's usually only used after someone discover a bug leading to a stack overflow caused by recursive semantic. So my recommendation is only a preventive. I'm really not sure it is useful.

[ghost]

Mutually depedant types can lead to the problem. But mutually dependant types would lead to have the semantic run lazily at from another place, making the bug fixed here impossible to happen...

let's say my suggestion can be ignored.