add InstalledBackend struct

Author: Firestar99

crates/cargo-gpu/src/build.rs

@@ -2,9 +2,9 @@
 #![allow(clippy::unwrap_used, reason = "this is basically a test")]
 //! `cargo gpu build`, analogous to `cargo build`
 
+use crate::install::Install;
 use crate::linkage::Linkage;
 use crate::lockfile::LockfileMismatchHandler;
-use crate::{install::Install, target_spec_dir};
 use anyhow::Context as _;
 use spirv_builder::{CompileResult, ModuleResult, SpirvBuilder};
 use std::io::Write as _;
@@ -59,22 +59,17 @@ pub struct Build {
 impl Build {
     /// Entrypoint
     pub fn run(&mut self) -> anyhow::Result<()> {
-        let (rustc_codegen_spirv_location, toolchain_channel) = self.install.run()?;
+        let installed_backend = self.install.run()?;
 
         let _lockfile_mismatch_handler = LockfileMismatchHandler::new(
             &self.install.shader_crate,
-            &toolchain_channel,
+            &installed_backend.toolchain_channel,
             self.install.force_overwrite_lockfiles_v4_to_v3,
         )?;
 
         let builder = &mut self.build.spirv_builder;
-        builder.rustc_codegen_spirv_location = Some(rustc_codegen_spirv_location);
-        builder.toolchain_overwrite = Some(toolchain_channel);
         builder.path_to_crate = Some(self.install.shader_crate.clone());
-        builder.path_to_target_spec = Some(target_spec_dir()?.join(format!(
-            "{}.json",
-            builder.target.as_ref().context("expect target to be set")?
-        )));
+        installed_backend.configure_spirv_builder(builder)?;
 
         // Ensure the shader output dir exists
         log::debug!(

crates/cargo-gpu/src/install.rs

@@ -6,7 +6,7 @@ use crate::spirv_source::{
 use crate::{cache_dir, spirv_source::SpirvSource, target_spec_dir};
 use anyhow::Context as _;
 use log::trace;
-use spirv_builder::TARGET_SPECS;
+use spirv_builder::{SpirvBuilder, TARGET_SPECS};
 use std::io::Write as _;
 use std::path::{Path, PathBuf};
 
@@ -77,6 +77,40 @@ pub struct Install {
     pub force_overwrite_lockfiles_v4_to_v3: bool,
 }
 
+/// Represents a functional backend installation, whether it was cached or just installed.
+#[derive(Clone, Debug)]
+pub struct InstalledBackend {
+    /// path to the rustc_codegen_spirv dylib
+    pub rustc_codegen_spirv_location: PathBuf,
+    /// toolchain channel name
+    pub toolchain_channel: String,
+}
+
+impl InstalledBackend {
+    /// Creates a new `SpirvBuilder` configured to use this installed backend.
+    pub fn to_spirv_builder(
+        &self,
+        path_to_crate: impl AsRef<Path>,
+        target: impl Into<String>,
+    ) -> SpirvBuilder {
+        let mut builder = SpirvBuilder::new(path_to_crate, target);
+        self.configure_spirv_builder(&mut builder)
+            .expect("unreachable");
+        builder
+    }
+
+    /// Configures the supplied [`SpirvBuilder`]. `SpirvBuilder.target` must be set and must not change after calling this function.
+    pub fn configure_spirv_builder(&self, builder: &mut SpirvBuilder) -> anyhow::Result<()> {
+        builder.rustc_codegen_spirv_location = Some(self.rustc_codegen_spirv_location.clone());
+        builder.toolchain_overwrite = Some(self.toolchain_channel.clone());
+        builder.path_to_target_spec = Some(target_spec_dir()?.join(format!(
+            "{}.json",
+            builder.target.as_ref().context("expect target to be set")?
+        )));
+        Ok(())
+    }
+}
+
 impl Default for Install {
     #[inline]
     fn default() -> Self {
@@ -164,7 +198,7 @@ package = "rustc_codegen_spirv"
 
     /// Install the binary pair and return the `(dylib_path, toolchain_channel)`.
     #[expect(clippy::too_many_lines, reason = "it's fine")]
-    pub fn run(&mut self) -> anyhow::Result<(PathBuf, String)> {
+    pub fn run(&mut self) -> anyhow::Result<InstalledBackend> {
         // Ensure the cache dir exists
         let cache_dir = cache_dir()?;
         log::info!("cache directory is '{}'", cache_dir.display());
@@ -282,6 +316,9 @@ package = "rustc_codegen_spirv"
                 .context("writing target spec files")?;
         }
 
-        Ok((dest_dylib_path, toolchain_channel))
+        Ok(InstalledBackend {
+            rustc_codegen_spirv_location: dest_dylib_path,
+            toolchain_channel,
+        })
     }
 }