[MIR] Cannot explicitly set discriminant

[scottcarr]

In #35168, we might like to deaggregate enums like:

x = Foo::Bar{a: 0, b: 0};

Into:

(x as Foo::Bar).0 = 0;
(x as Foo:Bar).1 = 0;

The problem (as far I know) is that the deaggregated version never sets the discrimnant.

I had some code that at least did the casting:

// if we handled enums:
let lhs_cast = if adt_def.variants.len() > 1 {
     Lvalue::Projection(Box::new(LvalueProjection {
         base: ai.lhs.clone(),
         elem: ProjectionElem::Downcast(ai.adt_def, ai.variant),
     }))
 } else {
     lhs_cast
};

[nagisa]

I have long wanted to add a Discriminant lvalue projection. Might be a time to do it.

[nikomatsakis]

Could also use it to rewrite Switch vs SwitchInt, which I think @nagisa was in favor of :)

[bluss]

Is this fixed now?

[nagisa]

The original issue is fixed, yes.

[bluss]

Closed as fixed by #35348