UE uses "unnamed struct" and Slang needs to support

[jkwak-work]

Unreal Engine expects the following HLSL syntax to work properly.

static const struct
{
    int member;
} varName = { value };

But Slang errors out as following,

c.slang(2): error 20001: unexpected '{', expected identifier
{
^

The following syntax works for Slang but we need to support what UE expects.

struct StructName
{
    int member;
};
static const StructName varName = { value };