Build and install workspace members that are dependencies by default (#14663)

Regardless of the presence of a build system, as in
#14413

---------

Co-authored-by: John Mumm <[email protected]>

Author: zanieb

crates/uv-distribution/src/metadata/lowering.rs

@@ -306,7 +306,10 @@ impl LoweredRequirement {
                                     },
                                     url,
                                 }
-                            } else if member.pyproject_toml().is_package() {
+                            } else if member
+                                .pyproject_toml()
+                                .is_package(!workspace.is_required_member(&requirement.name))
+                            {
                                 RequirementSource::Directory {
                                     install_path: install_path.into_boxed_path(),
                                     url,
@@ -736,7 +739,8 @@ fn path_source(
                 fs_err::read_to_string(&pyproject_path)
                     .ok()
                     .and_then(|contents| PyProjectToml::from_string(contents).ok())
-                    .and_then(|pyproject_toml| pyproject_toml.tool_uv_package())
+                    // We don't require a build system for path dependencies
+                    .map(|pyproject_toml| pyproject_toml.is_package(false))
                     .unwrap_or(true)
             });
 

crates/uv-platform-tags/src/tags.rs

@@ -771,7 +771,7 @@ mod tests {
     /// A reference list can be generated with:
     /// ```text
     /// $ python -c "from packaging import tags; [print(tag) for tag in tags.platform_tags()]"`
-    /// ````
+    /// ```
     #[test]
     fn test_platform_tags_manylinux() {
         let tags = compatible_tags(&Platform::new(

crates/uv-resolver/src/lock/mod.rs

@@ -1255,6 +1255,7 @@ impl Lock {
         root: &Path,
         packages: &BTreeMap<PackageName, WorkspaceMember>,
         members: &[PackageName],
+        required_members: &BTreeSet<PackageName>,
         requirements: &[Requirement],
         constraints: &[Requirement],
         overrides: &[Requirement],
@@ -1282,7 +1283,10 @@ impl Lock {
         // Validate that the member sources have not changed (e.g., that they've switched from
         // virtual to non-virtual or vice versa).
         for (name, member) in packages {
-            let expected = !member.pyproject_toml().is_package();
+            // We don't require a build system, if the workspace member is a dependency
+            let expected = !member
+                .pyproject_toml()
+                .is_package(!required_members.contains(name));
             let actual = self
                 .find_by_name(name)
                 .ok()

crates/uv-workspace/src/pyproject.rs

@@ -66,7 +66,7 @@ pub struct PyProjectToml {
 
     /// Used to determine whether a `build-system` section is present.
     #[serde(default, skip_serializing)]
-    build_system: Option<serde::de::IgnoredAny>,
+    pub build_system: Option<serde::de::IgnoredAny>,
 }
 
 impl PyProjectToml {
@@ -81,18 +81,18 @@ impl PyProjectToml {
 
     /// Returns `true` if the project should be considered a Python package, as opposed to a
     /// non-package ("virtual") project.
-    pub fn is_package(&self) -> bool {
+    pub fn is_package(&self, require_build_system: bool) -> bool {
         // If `tool.uv.package` is set, defer to that explicit setting.
         if let Some(is_package) = self.tool_uv_package() {
             return is_package;
         }
 
         // Otherwise, a project is assumed to be a package if `build-system` is present.
-        self.build_system.is_some()
+        self.build_system.is_some() || !require_build_system
     }
 
     /// Returns the value of `tool.uv.package` if set.
-    pub fn tool_uv_package(&self) -> Option<bool> {
+    fn tool_uv_package(&self) -> Option<bool> {
         self.tool
             .as_ref()
             .and_then(|tool| tool.uv.as_ref())

crates/uv-workspace/src/workspace.rs

@@ -20,7 +20,7 @@ use uv_warnings::warn_user_once;
 
 use crate::dependency_groups::{DependencyGroupError, FlatDependencyGroup, FlatDependencyGroups};
 use crate::pyproject::{
-    Project, PyProjectToml, PyprojectTomlError, Sources, ToolUvSources, ToolUvWorkspace,
+    Project, PyProjectToml, PyprojectTomlError, Source, Sources, ToolUvSources, ToolUvWorkspace,
 };
 
 type WorkspaceMembers = Arc<BTreeMap<PackageName, WorkspaceMember>>;
@@ -109,6 +109,8 @@ pub struct Workspace {
     install_path: PathBuf,
     /// The members of the workspace.
     packages: WorkspaceMembers,
+    /// The workspace members that are required by other members.
+    required_members: BTreeSet<PackageName>,
     /// The sources table from the workspace `pyproject.toml`.
     ///
     /// This table is overridden by the project sources.
@@ -260,6 +262,7 @@ impl Workspace {
         pyproject_toml: PyProjectToml,
     ) -> Option<Self> {
         let mut packages = self.packages;
+
         let member = Arc::make_mut(&mut packages).get_mut(package_name)?;
 
         if member.root == self.install_path {
@@ -279,17 +282,33 @@ impl Workspace {
             // Set the `pyproject.toml` for the member.
             member.pyproject_toml = pyproject_toml;
 
+            // Recompute required_members with the updated data
+            let required_members = Self::collect_required_members(
+                &packages,
+                &workspace_sources,
+                &workspace_pyproject_toml,
+            );
+
             Some(Self {
                 pyproject_toml: workspace_pyproject_toml,
                 sources: workspace_sources,
                 packages,
+                required_members,
                 ..self
             })
         } else {
             // Set the `pyproject.toml` for the member.
             member.pyproject_toml = pyproject_toml;
 
-            Some(Self { packages, ..self })
+            // Recompute required_members with the updated member data
+            let required_members =
+                Self::collect_required_members(&packages, &self.sources, &self.pyproject_toml);
+
+            Some(Self {
+                packages,
+                required_members,
+                ..self
+            })
         }
     }
 
@@ -303,7 +322,7 @@ impl Workspace {
 
     /// Returns the set of all workspace members.
     pub fn members_requirements(&self) -> impl Iterator<Item = Requirement> + '_ {
-        self.packages.values().filter_map(|member| {
+        self.packages.iter().filter_map(|(name, member)| {
             let url = VerbatimUrl::from_absolute_path(&member.root)
                 .expect("path is valid URL")
                 .with_given(member.root.to_string_lossy());
@@ -312,7 +331,10 @@ impl Workspace {
                 extras: Box::new([]),
                 groups: Box::new([]),
                 marker: MarkerTree::TRUE,
-                source: if member.pyproject_toml.is_package() {
+                source: if member
+                    .pyproject_toml()
+                    .is_package(!self.is_required_member(name))
+                {
                     RequirementSource::Directory {
                         install_path: member.root.clone().into_boxed_path(),
                         editable: Some(true),
@@ -332,9 +354,65 @@ impl Workspace {
         })
     }
 
+    /// The workspace members that are required my another member of the workspace.
+    pub fn required_members(&self) -> &BTreeSet<PackageName> {
+        &self.required_members
+    }
+
+    /// Compute the workspace members that are required by another member of the workspace.
+    ///
+    /// N.B. this checks if a workspace member is required by inspecting `tool.uv.source` entries,
+    /// but does not actually check if the source is _used_, which could result in false positives
+    /// but is easier to compute.
+    fn collect_required_members(
+        packages: &BTreeMap<PackageName, WorkspaceMember>,
+        sources: &BTreeMap<PackageName, Sources>,
+        pyproject_toml: &PyProjectToml,
+    ) -> BTreeSet<PackageName> {
+        sources
+            .iter()
+            .filter(|(name, _)| {
+                pyproject_toml
+                    .project
+                    .as_ref()
+                    .is_none_or(|project| project.name != **name)
+            })
+            .chain(
+                packages
+                    .iter()
+                    .filter_map(|(name, member)| {
+                        member
+                            .pyproject_toml
+                            .tool
+                            .as_ref()
+                            .and_then(|tool| tool.uv.as_ref())
+                            .and_then(|uv| uv.sources.as_ref())
+                            .map(ToolUvSources::inner)
+                            .map(move |sources| {
+                                sources
+                                    .iter()
+                                    .filter(move |(source_name, _)| name != *source_name)
+                            })
+                    })
+                    .flatten(),
+            )
+            .filter_map(|(package, sources)| {
+                sources
+                    .iter()
+                    .any(|source| matches!(source, Source::Workspace { .. }))
+                    .then_some(package.clone())
+            })
+            .collect()
+    }
+
+    /// Whether a given workspace member is required by another member.
+    pub fn is_required_member(&self, name: &PackageName) -> bool {
+        self.required_members().contains(name)
+    }
+
     /// Returns the set of all workspace member dependency groups.
     pub fn group_requirements(&self) -> impl Iterator<Item = Requirement> + '_ {
-        self.packages.values().filter_map(|member| {
+        self.packages.iter().filter_map(|(name, member)| {
             let url = VerbatimUrl::from_absolute_path(&member.root)
                 .expect("path is valid URL")
                 .with_given(member.root.to_string_lossy());
@@ -368,7 +446,10 @@ impl Workspace {
                 extras: Box::new([]),
                 groups: groups.into_boxed_slice(),
                 marker: MarkerTree::TRUE,
-                source: if member.pyproject_toml.is_package() {
+                source: if member
+                    .pyproject_toml()
+                    .is_package(!self.is_required_member(name))
+                {
                     RequirementSource::Directory {
                         install_path: member.root.clone().into_boxed_path(),
                         editable: Some(true),
@@ -746,9 +827,16 @@ impl Workspace {
             .and_then(|uv| uv.index)
             .unwrap_or_default();
 
+        let required_members = Self::collect_required_members(
+            &workspace_members,
+            &workspace_sources,
+            &workspace_pyproject_toml,
+        );
+
         Ok(Workspace {
             install_path: workspace_root,
             packages: workspace_members,
+            required_members,
             sources: workspace_sources,
             indexes: workspace_indexes,
             pyproject_toml: workspace_pyproject_toml,
@@ -1232,15 +1320,23 @@ impl ProjectWorkspace {
                 project.name.clone(),
                 current_project,
             )]));
+            let workspace_sources = BTreeMap::default();
+            let required_members = Workspace::collect_required_members(
+                &current_project_as_members,
+                &workspace_sources,
+                project_pyproject_toml,
+            );
+
             return Ok(Self {
                 project_root: project_path.clone(),
                 project_name: project.name.clone(),
                 workspace: Workspace {
                     install_path: project_path.clone(),
                     packages: current_project_as_members,
+                    required_members,
                     // There may be package sources, but we don't need to duplicate them into the
                     // workspace sources.
-                    sources: BTreeMap::default(),
+                    sources: workspace_sources,
                     indexes: Vec::default(),
                     pyproject_toml: project_pyproject_toml.clone(),
                 },
@@ -1692,6 +1788,7 @@ mod tests {
                 "pyproject_toml": "[PYPROJECT_TOML]"
               }
             },
+            "required_members": [],
             "sources": {},
             "indexes": [],
             "pyproject_toml": {
@@ -1745,6 +1842,7 @@ mod tests {
                     "pyproject_toml": "[PYPROJECT_TOML]"
                   }
                 },
+                "required_members": [],
                 "sources": {},
                 "indexes": [],
                 "pyproject_toml": {
@@ -1825,6 +1923,10 @@ mod tests {
                     "pyproject_toml": "[PYPROJECT_TOML]"
                   }
                 },
+                "required_members": [
+                  "bird-feeder",
+                  "seeds"
+                ],
                 "sources": {
                   "bird-feeder": [
                     {
@@ -1946,6 +2048,10 @@ mod tests {
                     "pyproject_toml": "[PYPROJECT_TOML]"
                   }
                 },
+                "required_members": [
+                  "bird-feeder",
+                  "seeds"
+                ],
                 "sources": {},
                 "indexes": [],
                 "pyproject_toml": {
@@ -2013,6 +2119,7 @@ mod tests {
                     "pyproject_toml": "[PYPROJECT_TOML]"
                   }
                 },
+                "required_members": [],
                 "sources": {},
                 "indexes": [],
                 "pyproject_toml": {
@@ -2147,6 +2254,7 @@ mod tests {
                     "pyproject_toml": "[PYPROJECT_TOML]"
                   }
                 },
+                "required_members": [],
                 "sources": {},
                 "indexes": [],
                 "pyproject_toml": {
@@ -2254,6 +2362,7 @@ mod tests {
                     "pyproject_toml": "[PYPROJECT_TOML]"
                   }
                 },
+                "required_members": [],
                 "sources": {},
                 "indexes": [],
                 "pyproject_toml": {
@@ -2375,6 +2484,7 @@ mod tests {
                     "pyproject_toml": "[PYPROJECT_TOML]"
                   }
                 },
+                "required_members": [],
                 "sources": {},
                 "indexes": [],
                 "pyproject_toml": {
@@ -2470,6 +2580,7 @@ mod tests {
                     "pyproject_toml": "[PYPROJECT_TOML]"
                   }
                 },
+                "required_members": [],
                 "sources": {},
                 "indexes": [],
                 "pyproject_toml": {

crates/uv/src/commands/build_frontend.rs

@@ -263,7 +263,7 @@ async fn build_impl(
             .get(package)
             .ok_or_else(|| anyhow::anyhow!("Package `{package}` not found in workspace"))?;
 
-        if !package.pyproject_toml().is_package() {
+        if !package.pyproject_toml().is_package(true) {
             let name = &package.project().name;
             let pyproject_toml = package.root().join("pyproject.toml");
             return Err(anyhow::anyhow!(
@@ -300,7 +300,7 @@ async fn build_impl(
         let packages: Vec<_> = workspace
             .packages()
             .values()
-            .filter(|package| package.pyproject_toml().is_package())
+            .filter(|package| package.pyproject_toml().is_package(true))
             .map(|package| AnnotatedSource {
                 source: Source::Directory(Cow::Borrowed(package.root())),
                 package: Some(package.project().name.clone()),