[Migrated] Allow keeping linkage annotation

Issue automatically imported from old repo: https://github.com/EmbarkStudios/rust-gpu/issues/1042
Old labels: t: enhancement
Originally creatd by SiebenCorgie on 2023-04-21T16:42:49Z

SpirV allows defining import and export [0] for linking separate Shader modules [1] post compilation.

Apparently SpirV linking is already used within rust-gpu, but not exposed. Therefore we can't use extern "C" as we usually would.

This functionality would be useful, for instance when building shader permutation systems.

The enhancement would basically be allowing extern C, #[no_mangle] etc. to map to (possibly named) import/export decorated values whenever the Linkage capability on spirv-builder is enabled.

spirv-builder の Linkage capability から始め、リンクされている SPIR-V linkage 仕様を確認してください。rust-gpu が現在 extern "C" と #[no_mangle" の値をどのように扱っているかを追跡し、その後、名前付き import/export decorations への必要なマッピングを決定してください。Linkage が有効な場合に linkage annotations が保持され、別々の shader modules がそれらを使用できれば完了です。