Fix NameExprType returning deleted canonical type when it's in a generic parent.

fixes #339

`NamedExpressionType::CreateCanonicalType()` may return a deleted pointer. The original implementation is as follows:
```
    Type* NamedExpressionType::CreateCanonicalType()
    {
        return GetType(declRef)->GetCanonicalType();
    }
```
If `GetType()` returns a newly constructed Type (this happens when the `typedef` is defined inside a generic parent, which triggers a non-trivial substitution), the temporary type will be deleted when the function returns. The fix is to store the temporary type as a field of NamedExpressionType (`innerType`).

A relevant fix (though not the true cause of issue #339) is to have `Type::GetCanonicalType()` also hold a `RefPtr` to the constructed canonical type, when the canonical type is not `this`. This prevents a returned canonical type being assigned to a RefPtr, which makes it possible for that RefPtr to be the sole owner of the canonical type and deleteing the canonical type when that RefPtr is destroyed.

1 files changed, 1 insertions, 0 deletions

diff --git a/source/slang/syntax-base-defs.h b/source/slang/syntax-base-defs.h
index fdb2694a9..1853125a8 100644
--- a/source/slang/syntax-base-defs.h
+++ b/source/slang/syntax-base-defs.h
@@ -121,6 +121,7 @@ protected:
 
     virtual Type* CreateCanonicalType() = 0;
     Type* canonicalType = nullptr;
+    RefPtr<Type> canonicalTypeRefPtr;
 
     Session* session = nullptr;
     )