fix: solve build source relative to the manifest path

crates/pixi_command_dispatcher/src/build_backend_metadata/mod.rs

@@ -138,7 +138,10 @@ impl BuildBackendMetadataSpec {
         } else if let Some(build_source) = &discovered_backend.init_params.build_source {
             Some(
                 command_dispatcher
-                    .pin_and_checkout(build_source.clone())
+                    .pin_and_checkout(
+                        build_source.clone(),
+                        Some(&discovered_backend.init_params.manifest_path),
+                    )
                     .await
                     .map_err_with(BuildBackendMetadataError::SourceCheckout)?,
             )

crates/pixi_command_dispatcher/src/command_dispatcher/mod.rs

@@ -565,7 +565,10 @@ impl CommandDispatcher {
     ///
     /// This function resolves the source specification to a concrete checkout
     /// by:
-    /// 1. For path sources: Resolving relative paths against the root directory
+    /// 1. For path sources: Resolving relative paths against the root directory or against an alternative root path
+    ///
+    /// i.e. in the case of an out-of-tree build.
+    ///
     /// 2. For git sources: Cloning or fetching the repository and checking out
     ///    the specified reference
     /// 3. For URL sources: Downloading and extracting the archive (currently
@@ -578,6 +581,7 @@ impl CommandDispatcher {
     pub async fn pin_and_checkout(
         &self,
         source_location_spec: SourceLocationSpec,
+        alternative_root_path: Option<&Path>,
     ) -> Result<SourceCheckout, CommandDispatcherError<SourceCheckoutError>> {
         match source_location_spec {
             SourceLocationSpec::Url(url) => {
@@ -586,7 +590,7 @@ impl CommandDispatcher {
             SourceLocationSpec::Path(path) => {
                 let source_path = self
                     .data
-                    .resolve_typed_path(path.path.to_path())
+                    .resolve_typed_path(path.path.to_path(), alternative_root_path)
                     .map_err(SourceCheckoutError::from)
                     .map_err(CommandDispatcherError::Failed)?;
                 Ok(SourceCheckout {
@@ -618,7 +622,7 @@ impl CommandDispatcher {
             PinnedSourceSpec::Path(ref path) => {
                 let source_path = self
                     .data
-                    .resolve_typed_path(path.path.to_path())
+                    .resolve_typed_path(path.path.to_path(), None)
                     .map_err(SourceCheckoutError::from)
                     .map_err(CommandDispatcherError::Failed)?;
                 Ok(SourceCheckout {
@@ -653,7 +657,11 @@ impl CommandDispatcherData {
     ///
     /// This function does not check if the path exists and also does not follow
     /// symlinks.
-    fn resolve_typed_path(&self, path_spec: Utf8TypedPath) -> Result<PathBuf, InvalidPathError> {
+    fn resolve_typed_path(
+        &self,
+        path_spec: Utf8TypedPath,
+        alternative_root_path: Option<&Path>,
+    ) -> Result<PathBuf, InvalidPathError> {
         if path_spec.is_absolute() {
             Ok(Path::new(path_spec.as_str()).to_path_buf())
         } else if let Ok(user_path) = path_spec.strip_prefix("~/") {
@@ -663,7 +671,10 @@ impl CommandDispatcherData {
             debug_assert!(home_dir.is_absolute());
             normalize_absolute_path(&home_dir.join(Path::new(user_path.as_str())))
         } else {
-            let root_dir = self.root_dir.as_path();
+            let root_dir = match alternative_root_path {
+                Some(root_path) => root_path,
+                None => self.root_dir.as_path(),
+            };
             let native_path = Path::new(path_spec.as_str());
             debug_assert!(root_dir.is_absolute());
             normalize_absolute_path(&root_dir.join(native_path))

crates/pixi_command_dispatcher/src/solve_pixi/source_metadata_collector.rs

@@ -171,7 +171,7 @@ impl SourceMetadataCollector {
         // will pick build_source; we only override the build pin later.
         let source = self
             .command_queue
-            .pin_and_checkout(spec.location)
+            .pin_and_checkout(spec.location, None)
             .await
             .map_err(|err| CollectSourceMetadataError::SourceCheckoutError {
                 name: name.as_source().to_string(),

crates/pixi_command_dispatcher/src/source_build/mod.rs

@@ -267,7 +267,16 @@ impl SourceBuildSpec {
             discovered_backend.init_params.build_source.clone()
         {
             let build_source_checkout = command_dispatcher
-                .pin_and_checkout(manifest_build_source)
+                .pin_and_checkout(
+                    manifest_build_source,
+                    Some(
+                        discovered_backend
+                            .init_params
+                            .manifest_path
+                            .parent()
+                            .expect("manifest path should have a parent directory"),
+                    ),
+                )
                 .await
                 .map_err_with(SourceBuildError::SourceCheckout)?;
             build_source_checkout.path

crates/pixi_global/src/project/mod.rs

@@ -1372,7 +1372,7 @@ impl Project {
     ) -> Result<PackageName, InferPackageNameError> {
         let command_dispatcher = self.command_dispatcher()?;
         let checkout = command_dispatcher
-            .pin_and_checkout(source_spec.location)
+            .pin_and_checkout(source_spec.location, None)
             .await
             .map_err(|e| InferPackageNameError::BuildBackendMetadata(Box::new(e)))?;