nix: use rustc_codegen_spirv.so from nix

Author: timon-schelling

node-graph/graster-nodes/shaders/build.rs

@@ -1,3 +1,4 @@
+use cargo_gpu::InstalledBackend;
 use cargo_gpu::spirv_builder::{MetadataPrintout, SpirvMetadata};
 use std::path::PathBuf;
 
@@ -6,8 +7,29 @@ pub fn main() -> Result<(), Box<dyn std::error::Error>> {
 
 	let shader_crate = PathBuf::from(concat!(env!("CARGO_MANIFEST_DIR"), "/.."));
 
-	// install the toolchain and build the `rustc_codegen_spirv` codegen backend with it
-	let backend = cargo_gpu::Install::from_shader_crate(shader_crate.clone()).run()?;
+	// Allows overriding the PATH to inject the rust-gpu rust toolchain when building the rest of the project with stable rustc.
+	// Used in nix shell. Do not remove without checking with developers using nix.
+	if let Ok(path_override) = std::env::var("RUST_GPU_PATH_OVERRIDE") {
+		let current_path = std::env::var("PATH").unwrap_or_default();
+		let new_path = format!("{path_override}:{current_path}");
+		// SAFETY: Build script is single-threaded therefore this cannot lead to undefined behavior.
+		unsafe {
+			std::env::set_var("PATH", &new_path);
+		}
+	}
+
+	let rustc_codegen_spirv_path = std::env::var("RUSTC_CODEGEN_SPIRV_PATH").unwrap_or_default();
+	let backend = if rustc_codegen_spirv_path.is_empty() {
+		// install the toolchain and build the `rustc_codegen_spirv` codegen backend with it
+		cargo_gpu::Install::from_shader_crate(shader_crate.clone()).run()?
+	} else {
+		// use the `RUSTC_CODEGEN_SPIRV` environment variable to find the codegen backend
+		let mut backend = InstalledBackend::default();
+		backend.rustc_codegen_spirv_location = PathBuf::from(rustc_codegen_spirv_path);
+		backend.toolchain_channel = "nightly".to_string();
+		backend.target_spec_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+		backend
+	};
 
 	// build the shader crate
 	let mut builder = backend.to_spirv_builder(shader_crate, "spirv-unknown-naga-wgsl");

node-graph/graster-nodes/shaders/spirv-unknown-naga-wgsl.json

@@ -0,0 +1,26 @@
+{
+	"allows-weak-linkage": false,
+	"arch": "spirv",
+	"crt-objects-fallback": "false",
+	"crt-static-allows-dylibs": true,
+	"crt-static-respected": true,
+	"data-layout": "e-m:e-p:32:32:32-i64:64-n8:16:32:64",
+	"dll-prefix": "",
+	"dll-suffix": ".spv.json",
+	"dynamic-linking": true,
+	"emit-debug-gdb-scripts": false,
+	"env": "naga-wgsl",
+	"linker-flavor": "unix",
+	"linker-is-gnu": false,
+	"llvm-target": "spirv-unknown-naga-wgsl",
+	"main-needs-argc-argv": false,
+	"metadata": {
+		"description": null,
+		"host_tools": null,
+		"std": null,
+		"tier": null
+	},
+	"panic-strategy": "abort",
+	"simd-types-indirect": false,
+	"target-pointer-width": "32"
+}