Add a better error message for common global generic failure (#634)

A common mistake that seems to come up when using global generic type parameters:

```hlsl
interface IHero { ... }
type_param H : IHero;
ParameterBlock<H> gHero;
```

is to accidentally try to specialize the type parameter `H` using `H` itself as the argument (instead of some concrete type like `Batman`). The current front-end checks naively let this pass, because `H` satisfies all the requirements (it sure does declare that it implements `IHero`, which is the only requirement we have). This currently leads to downstream failure when we generate code with generic type parameters still left in the IR.

This change implements a simple fix which is to:

- Check when we are trying to specialize a global generic parameter using another global generic parameter, since this is currently always a mistake

- Add a special-case diagnostic for the 99% case of this failure, which is specializing a type parameter to itself

This fix is primarily motivated by the way generics support will initially be implemented in Falcor.

0 files changed, 0 insertions, 0 deletions