# Objective
Currently, shaders may only have syntax such as
```wgsl
#ifdef FOO
// foo code
#else
#ifdef BAR
// bar code
#else
#ifdef BAZ
// baz code
#else
// fallback code
#endif
#endif
#endif
```
This is hard to read and follow.
Add a way to allow writing `#else ifdef DEFINE` to reduce the number of scopes introduced and to increase readability.
## Solution
Refactor the current preprocessing a bit and add logic to allow `#else ifdef DEFINE`.
This includes per-scope tracking of whether a branch has been accepted.
Add a few tests for this feature.
With these changes we may now write:
```wgsl
#ifdef FOO
// foo code
#else ifdef BAR
// bar code
#else ifdef BAZ
// baz code
#else
// fallback code
#endif
```
instead.
---
## Changelog
- Add `#else ifdef` to shader preprocessing.
12f30f5667