Shaderdef values break shader imports

[aevyrie]

Bevy version

All commits after d44e865

What you did

Followed migration instructions in the PR.

What went wrong

Shader error with:

2022-12-21T07:05:18.759671Z ERROR bevy_render::render_resource::pipeline_cache: failed to process shader:
error: expected constant, found '#'
   ┌─ wgsl:44:49
   │
44 │     directional_lights: array<DirectionalLight, #{MAX_DIRECTIONAL_LIGHTS}u>,
   │                                                 ^ expected constant

Additional information

It appears that PR #5900 breaks imports, because those imports now depend on shaderdefs which users may not have available. In my case, I was attempting to import:

#import bevy_pbr::mesh_view_types

so I could use the View struct, which was giving me the error posted above. The problem was that the import was bringing structs into scope that referred to the MAX_DIRECTIONAL_LIGHTS shaderdef, which my shader did not use. Specifically, it was erroring when it reached struct Lights:

struct Lights {
    // NOTE: this array size must be kept in sync with the constants defined in bevy_pbr/src/render/light.rs
    directional_lights: array<DirectionalLight, #{MAX_DIRECTIONAL_LIGHTS}u>,

[aevyrie]

I've added this to the 0.10 milestone to ensure at minimum this breaking change is documented prior to release, as the PR does not mention this in the migration guide.

[torsteingrindvik]

Duplicate?
#6799

EDIT: Ping @mockersf

[aevyrie]

Yup, this is a duplicate, I was searching for shaderdefs and didn't find it.