fix: ensure -p package is resolved to shader crate before build and install commands are reconstructed

crates/cargo-gpu/src/build.rs

@@ -61,9 +61,7 @@ impl Build {
         let installed_backend = self.install.run()?;
         let mut metadata = crate::metadata::MetadataCache::default();
 
-        if let Some(package) = self.install.package.as_ref() {
-            self.install.shader_crate = metadata.resolve_package_to_shader_crate(package)?;
-        }
+        self.install.shader_crate = self.install.get_resolved_shader_crate(&mut metadata)?;
 
         let _lockfile_mismatch_handler = LockfileMismatchHandler::new(
             &self.install.shader_crate,

crates/cargo-gpu/src/install.rs

@@ -4,6 +4,7 @@ use crate::spirv_source::{
     get_channel_from_rustc_codegen_spirv_build_script, query_metadata, FindPackage as _,
 };
 use crate::target_specs::update_target_specs_files;
+use crate::MetadataCache;
 use crate::{cache_dir, spirv_source::SpirvSource};
 use anyhow::Context as _;
 use spirv_builder::SpirvBuilder;
@@ -150,6 +151,24 @@ impl Install {
         }
     }
 
+    /// Resolves a possible workspace package passed with `-p {package}` to its shader crate path,
+    /// as if it had been passed with `--shader-crate {package-parent-path}`.
+    ///
+    /// If no such package was passed, this resolves to the shader crate passed, or the default.
+    ///
+    /// ## Errors
+    /// Errs if the metadata cache cannot resolve the shader crate.
+    /// See [`MetadataCache::resolve_package_to_shader_crate`] for more info.
+    pub fn get_resolved_shader_crate(
+        &self,
+        metadata: &mut MetadataCache,
+    ) -> anyhow::Result<std::path::PathBuf> {
+        self.package.as_ref().map_or_else(
+            || Ok(self.shader_crate.clone()),
+            |package| metadata.resolve_package_to_shader_crate(package),
+        )
+    }
+
     /// Create the `rustc_codegen_spirv_dummy` crate that depends on `rustc_codegen_spirv`
     fn write_source_files(source: &SpirvSource, checkout: &Path) -> anyhow::Result<()> {
         // skip writing a dummy project if we use a local rust-gpu checkout

crates/cargo-gpu/src/lib.rs

@@ -128,9 +128,12 @@ impl Command {
     ) -> anyhow::Result<()> {
         match &self {
             Self::Install(install) => {
-                let shader_crate_path = &install.shader_crate;
+                // NOTE: Here `install` is only used for its `shader_crate` field, the rest is
+                // not used, as config::Config::clap_command_with_cargo_config reconstructs
+                // the command from the environment.
+                let shader_crate_path = install.get_resolved_shader_crate(metadata_cache)?;
                 let command = config::Config::clap_command_with_cargo_config(
-                    shader_crate_path,
+                    &shader_crate_path,
                     env_args,
                     metadata_cache,
                 )?;
@@ -141,9 +144,12 @@ impl Command {
                 command.install.run()?;
             }
             Self::Build(build) => {
-                let shader_crate_path = &build.install.shader_crate;
+                // NOTE: Here `build` is only used for its `shader_crate` field, the rest is
+                // not used, as config::Config::clap_command_with_cargo_config reconstructs
+                // the command from the environment.
+                let shader_crate_path = build.install.get_resolved_shader_crate(metadata_cache)?;
                 let mut command = config::Config::clap_command_with_cargo_config(
-                    shader_crate_path,
+                    &shader_crate_path,
                     env_args,
                     metadata_cache,
                 )?;