Feature-gate gfx-rs/rspirv dependency

Because our `spirv-builder-cli` can modify itself to comply with various
versions of `spirv-builder` from `rust-gpu`, then we also need to match
the version of `spirv` that we use to get `spirv::Capabilities`.

Namely that `rust-gpu <= v0.9.0` uses `spirv = "0.2.0"` and that
`rust-gpu >= "v0.9.0"` uses `spirv = "0.3.0".

Another solution to this could be to re-export `spirv` from `spirv-builder`.
But I'm not sure that would avoid compiling the entirety of `spirv-builder`
(which depends on specific Rust nightly versions), and besides, it's not
trivial to retroactively add re-exports to already-published version of
`rust-gpu`.

crates/cargo-gpu/Cargo.toml

@@ -11,7 +11,7 @@ build = "build.rs"
 
 [dependencies]
 anyhow.workspace = true
-spirv-builder-cli = { path = "../spirv-builder-cli", default-features = false }
+spirv-builder-cli = { path = "../spirv-builder-cli", default-features = false, features = ["rspirv-latest"] }
 clap.workspace = true
 directories.workspace = true
 env_logger.workspace = true

crates/spirv-builder-cli/Cargo.toml

@@ -10,16 +10,29 @@ env_logger = "0.10"
 log = "0.4"
 serde = "1.0.214"
 serde_json = "1.0.132"
-spirv = { version = "0.3.0", features = [ "deserialize", "serialize" ] }
 toml = "0.8.19"
 
 [features]
 default = ["spirv-builder-0_10"]
 # The `spirv-builder` before `cargo gpu` existed. It has an incompatible `SpirvBuilder` interface.
-spirv-builder-pre-cli = ["dep:spirv-builder-pre-cli"]
+spirv-builder-pre-cli = ["dep:spirv-builder-pre-cli", "dep:spirv_0_2"]
 # The first version that introduced `cargo gpu`. It has some extra `.builder()` args that make
 # dynamically changing build dependencies easier.
-spirv-builder-0_10 = ["dep:spirv-builder-0_10"]
+spirv-builder-0_10 = ["dep:spirv-builder-0_10", "dep:spirv_0_3"]
+#
+rspirv-latest = ["dep:spirv_0_3"]
+
+[dependencies.spirv_0_2]
+package = "spirv"
+version = "0.2.0"
+features = [ "deserialize", "serialize" ]
+optional = true
+
+[dependencies.spirv_0_3]
+package = "spirv"
+version = "0.3.0"
+features = [ "deserialize", "serialize" ]
+optional = true
 
 # NB: All the `${AUTO-REPLACE*}` tokens in each feature get replaced with the same values.
 # This is because only one feature can ever be used at once and it makes it easier to just

crates/spirv-builder-cli/src/args.rs

@@ -1,3 +1,9 @@
+#[cfg(feature = "spirv-builder-pre-cli")]
+use spirv_0_2 as spirv;
+
+#[cfg(any(feature = "spirv-builder-0_10", feature = "rspirv-latest"))]
+use spirv_0_3 as spirv;
+
 use std::str::FromStr as _;
 
 #[derive(clap::Parser, Debug, serde::Deserialize, serde::Serialize)]

crates/spirv-builder-cli/src/lib.rs

@@ -1,6 +1,10 @@
 pub mod args;
 
-pub use spirv;
+#[cfg(feature = "spirv-builder-pre-cli")]
+pub use spirv_0_2 as spirv;
+
+#[cfg(any(feature = "spirv-builder-0_10", feature = "rspirv-latest"))]
+pub use spirv_0_3 as spirv;
 
 /// Shader source and entry point that can be used to create shader linkage.
 #[derive(serde::Serialize, Debug, PartialEq, Eq, PartialOrd, Ord)]