Add extra-build-dependencies

crates/uv-bench/benches/uv.rs

@@ -141,6 +141,7 @@ mod resolver {
         universal: bool,
     ) -> Result<ResolverOutput> {
         let build_isolation = BuildIsolation::default();
+        let extra_build_requires = uv_distribution::ExtraBuildRequires::default();
         let build_options = BuildOptions::default();
         let concurrency = Concurrency::default();
         let config_settings = ConfigSettings::default();
@@ -189,6 +190,7 @@ mod resolver {
             &config_settings,
             &config_settings_package,
             build_isolation,
+            &extra_build_requires,
             LinkMode::default(),
             &build_options,
             &hashes,

crates/uv-build-frontend/src/lib.rs

@@ -4,6 +4,7 @@
 
 mod error;
 
+use std::borrow::Cow;
 use std::ffi::OsString;
 use std::fmt::Formatter;
 use std::fmt::Write;
@@ -42,6 +43,7 @@ use uv_static::EnvVars;
 use uv_types::{AnyErrorBuild, BuildContext, BuildIsolation, BuildStack, SourceBuildTrait};
 use uv_warnings::warn_user_once;
 use uv_workspace::WorkspaceCache;
+use uv_workspace::pyproject::ExtraBuildDependencies;
 
 pub use crate::error::{Error, MissingHeaderCause};
 
@@ -281,6 +283,7 @@ impl SourceBuild {
         workspace_cache: &WorkspaceCache,
         config_settings: ConfigSettings,
         build_isolation: BuildIsolation<'_>,
+        extra_build_dependencies: &ExtraBuildDependencies,
         build_stack: &BuildStack,
         build_kind: BuildKind,
         mut environment_variables: FxHashMap<OsString, OsString>,
@@ -297,7 +300,6 @@ impl SourceBuild {
         };
 
         let default_backend: Pep517Backend = DEFAULT_BACKEND.clone();
-
         // Check if we have a PEP 517 build backend.
         let (pep517_backend, project) = Self::extract_pep517_backend(
             &source_tree,
@@ -322,6 +324,14 @@ impl SourceBuild {
             .or(fallback_package_version)
             .cloned();
 
+        let extra_build_dependencies: Vec<Requirement> = package_name
+            .as_ref()
+            .and_then(|name| extra_build_dependencies.get(name).cloned())
+            .unwrap_or_default()
+            .into_iter()
+            .map(Requirement::from)
+            .collect();
+
         // Create a virtual environment, or install into the shared environment if requested.
         let venv = if let Some(venv) = build_isolation.shared_environment(package_name.as_ref()) {
             venv.clone()
@@ -344,19 +354,26 @@ impl SourceBuild {
         if build_isolation.is_isolated(package_name.as_ref()) {
             debug!("Resolving build requirements");
 
+            let dependency_sources = if extra_build_dependencies.is_empty() {
+                "`build-system.requires`"
+            } else {
+                "`build-system.requires` and `extra-build-dependencies`"
+            };
+
             let resolved_requirements = Self::get_resolved_requirements(
                 build_context,
                 source_build_context,
                 &default_backend,
                 &pep517_backend,
+                extra_build_dependencies,
                 build_stack,
             )
             .await?;
 
             build_context
                 .install(&resolved_requirements, &venv, build_stack)
                 .await
-                .map_err(|err| Error::RequirementsInstall("`build-system.requires`", err.into()))?;
+                .map_err(|err| Error::RequirementsInstall(dependency_sources, err.into()))?;
         } else {
             debug!("Proceeding without build isolation");
         }
@@ -471,10 +488,13 @@ impl SourceBuild {
         source_build_context: SourceBuildContext,
         default_backend: &Pep517Backend,
         pep517_backend: &Pep517Backend,
+        extra_build_dependencies: Vec<Requirement>,
         build_stack: &BuildStack,
     ) -> Result<Resolution, Error> {
         Ok(
-            if pep517_backend.requirements == default_backend.requirements {
+            if pep517_backend.requirements == default_backend.requirements
+                && extra_build_dependencies.is_empty()
+            {
                 let mut resolution = source_build_context.default_resolution.lock().await;
                 if let Some(resolved_requirements) = &*resolution {
                     resolved_requirements.clone()
@@ -489,12 +509,25 @@ impl SourceBuild {
                     resolved_requirements
                 }
             } else {
+                let (requirements, dependency_sources) = if extra_build_dependencies.is_empty() {
+                    (
+                        Cow::Borrowed(&pep517_backend.requirements),
+                        "`build-system.requires`",
+                    )
+                } else {
+                    // If there are extra build dependencies, we need to resolve them together with
+                    // the backend requirements.
+                    let mut requirements = pep517_backend.requirements.clone();
+                    requirements.extend(extra_build_dependencies);
+                    (
+                        Cow::Owned(requirements),
+                        "`build-system.requires` and `extra-build-dependencies`",
+                    )
+                };
                 build_context
-                    .resolve(&pep517_backend.requirements, build_stack)
+                    .resolve(&requirements, build_stack)
                     .await
-                    .map_err(|err| {
-                        Error::RequirementsResolve("`build-system.requires`", err.into())
-                    })?
+                    .map_err(|err| Error::RequirementsResolve(dependency_sources, err.into()))?
             },
         )
     }
@@ -604,6 +637,7 @@ impl SourceBuild {
                             );
                         }
                     }
+
                     default_backend.clone()
                 };
                 Ok((backend, pyproject_toml.project))

crates/uv-cli/src/options.rs

@@ -354,6 +354,7 @@ pub fn resolver_options(
         }),
         no_build_isolation: flag(no_build_isolation, build_isolation, "build-isolation"),
         no_build_isolation_package: Some(no_build_isolation_package),
+        extra_build_dependencies: None,
         exclude_newer: ExcludeNewer::from_args(
             exclude_newer,
             exclude_newer_package.unwrap_or_default(),
@@ -475,6 +476,7 @@ pub fn resolver_installer_options(
         } else {
             Some(no_build_isolation_package)
         },
+        extra_build_dependencies: None,
         exclude_newer,
         exclude_newer_package: exclude_newer_package.map(ExcludeNewerPackage::from_iter),
         link_mode,

crates/uv-configuration/src/preview.rs

@@ -14,6 +14,7 @@ bitflags::bitflags! {
         const JSON_OUTPUT = 1 << 2;
         const PYLOCK = 1 << 3;
         const ADD_BOUNDS = 1 << 4;
+        const EXTRA_BUILD_DEPENDENCIES = 1 << 5;
     }
 }
 
@@ -28,6 +29,7 @@ impl PreviewFeatures {
             Self::JSON_OUTPUT => "json-output",
             Self::PYLOCK => "pylock",
             Self::ADD_BOUNDS => "add-bounds",
+            Self::EXTRA_BUILD_DEPENDENCIES => "extra-build-dependencies",
             _ => panic!("`flag_as_str` can only be used for exactly one feature flag"),
         }
     }
@@ -70,6 +72,7 @@ impl FromStr for PreviewFeatures {
                 "json-output" => Self::JSON_OUTPUT,
                 "pylock" => Self::PYLOCK,
                 "add-bounds" => Self::ADD_BOUNDS,
+                "extra-build-dependencies" => Self::EXTRA_BUILD_DEPENDENCIES,
                 _ => {
                     warn_user_once!("Unknown preview feature: `{part}`");
                     continue;
@@ -232,6 +235,10 @@ mod tests {
         assert_eq!(PreviewFeatures::JSON_OUTPUT.flag_as_str(), "json-output");
         assert_eq!(PreviewFeatures::PYLOCK.flag_as_str(), "pylock");
         assert_eq!(PreviewFeatures::ADD_BOUNDS.flag_as_str(), "add-bounds");
+        assert_eq!(
+            PreviewFeatures::EXTRA_BUILD_DEPENDENCIES.flag_as_str(),
+            "extra-build-dependencies"
+        );
     }
 
     #[test]

crates/uv-dispatch/src/lib.rs

@@ -22,6 +22,7 @@ use uv_configuration::{
 };
 use uv_configuration::{BuildOutput, Concurrency};
 use uv_distribution::DistributionDatabase;
+use uv_distribution::ExtraBuildRequires;
 use uv_distribution_filename::DistFilename;
 use uv_distribution_types::{
     CachedDist, DependencyMetadata, Identifier, IndexCapabilities, IndexLocations,
@@ -88,6 +89,7 @@ pub struct BuildDispatch<'a> {
     shared_state: SharedState,
     dependency_metadata: &'a DependencyMetadata,
     build_isolation: BuildIsolation<'a>,
+    extra_build_requires: &'a ExtraBuildRequires,
     link_mode: uv_install_wheel::LinkMode,
     build_options: &'a BuildOptions,
     config_settings: &'a ConfigSettings,
@@ -116,6 +118,7 @@ impl<'a> BuildDispatch<'a> {
         config_settings: &'a ConfigSettings,
         config_settings_package: &'a PackageConfigSettings,
         build_isolation: BuildIsolation<'a>,
+        extra_build_requires: &'a ExtraBuildRequires,
         link_mode: uv_install_wheel::LinkMode,
         build_options: &'a BuildOptions,
         hasher: &'a HashStrategy,
@@ -138,6 +141,7 @@ impl<'a> BuildDispatch<'a> {
             config_settings,
             config_settings_package,
             build_isolation,
+            extra_build_requires,
             link_mode,
             build_options,
             hasher,
@@ -219,6 +223,10 @@ impl BuildContext for BuildDispatch<'_> {
         &self.workspace_cache
     }
 
+    fn extra_build_dependencies(&self) -> &uv_workspace::pyproject::ExtraBuildDependencies {
+        &self.extra_build_requires.extra_build_dependencies
+    }
+
     async fn resolve<'data>(
         &'data self,
         requirements: &'data [Requirement],
@@ -452,6 +460,7 @@ impl BuildContext for BuildDispatch<'_> {
             self.workspace_cache(),
             config_settings,
             self.build_isolation,
+            &self.extra_build_requires.extra_build_dependencies,
             &build_stack,
             build_kind,
             self.build_extra_env_vars.clone(),

crates/uv-distribution/src/lib.rs

@@ -3,8 +3,8 @@ pub use download::LocalWheel;
 pub use error::Error;
 pub use index::{BuiltWheelIndex, RegistryWheelIndex};
 pub use metadata::{
-    ArchiveMetadata, BuildRequires, FlatRequiresDist, LoweredRequirement, LoweringError, Metadata,
-    MetadataError, RequiresDist, SourcedDependencyGroups,
+    ArchiveMetadata, BuildRequires, ExtraBuildRequires, FlatRequiresDist, LoweredRequirement,
+    LoweringError, Metadata, MetadataError, RequiresDist, SourcedDependencyGroups,
 };
 pub use reporter::Reporter;
 pub use source::prune;

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

@@ -4,7 +4,8 @@ use std::path::Path;
 use uv_configuration::SourceStrategy;
 use uv_distribution_types::{IndexLocations, Requirement};
 use uv_normalize::PackageName;
-use uv_workspace::pyproject::ToolUvSources;
+use uv_pypi_types::VerbatimParsedUrl;
+use uv_workspace::pyproject::{ExtraBuildDependencies, ToolUvSources};
 use uv_workspace::{
     DiscoveryOptions, MemberDiscovery, ProjectWorkspace, Workspace, WorkspaceCache,
 };
@@ -203,3 +204,93 @@ impl BuildRequires {
         })
     }
 }
+
+/// Lowered extra build dependencies with source resolution applied.
+#[derive(Debug, Clone, Default)]
+pub struct ExtraBuildRequires {
+    pub extra_build_dependencies: ExtraBuildDependencies,
+}
+
+impl ExtraBuildRequires {
+    /// Lower extra build dependencies from a workspace, applying source resolution.
+    pub fn from_workspace(
+        extra_build_dependencies: ExtraBuildDependencies,
+        workspace: &Workspace,
+        index_locations: &IndexLocations,
+        source_strategy: SourceStrategy,
+    ) -> Result<Self, MetadataError> {
+        match source_strategy {
+            SourceStrategy::Enabled => {
+                // Collect project sources and indexes
+                let project_indexes = workspace
+                    .pyproject_toml()
+                    .tool
+                    .as_ref()
+                    .and_then(|tool| tool.uv.as_ref())
+                    .and_then(|uv| uv.index.as_deref())
+                    .unwrap_or(&[]);
+
+                let empty_sources = BTreeMap::default();
+                let project_sources = workspace
+                    .pyproject_toml()
+                    .tool
+                    .as_ref()
+                    .and_then(|tool| tool.uv.as_ref())
+                    .and_then(|uv| uv.sources.as_ref())
+                    .map(ToolUvSources::inner)
+                    .unwrap_or(&empty_sources);
+
+                // Lower each package's extra build dependencies
+                let mut result = ExtraBuildDependencies::default();
+                for (package_name, requirements) in extra_build_dependencies {
+                    let lowered: Vec<uv_pep508::Requirement<VerbatimParsedUrl>> = requirements
+                        .into_iter()
+                        .flat_map(|requirement| {
+                            let requirement_name = requirement.name.clone();
+                            let extra = requirement.marker.top_level_extra_name();
+                            let group = None;
+                            LoweredRequirement::from_requirement(
+                                requirement,
+                                None,
+                                workspace.install_path(),
+                                project_sources,
+                                project_indexes,
+                                extra.as_deref(),
+                                group,
+                                index_locations,
+                                workspace,
+                                None,
+                            )
+                            .map(
+                                move |requirement| match requirement {
+                                    Ok(requirement) => Ok(requirement.into_inner().into()),
+                                    Err(err) => Err(MetadataError::LoweringError(
+                                        requirement_name.clone(),
+                                        Box::new(err),
+                                    )),
+                                },
+                            )
+                        })
+                        .collect::<Result<Vec<_>, _>>()?;
+                    result.insert(package_name, lowered);
+                }
+                Ok(Self {
+                    extra_build_dependencies: result,
+                })
+            }
+            SourceStrategy::Disabled => {
+                // Without source resolution, just return the dependencies as-is
+                Ok(Self {
+                    extra_build_dependencies,
+                })
+            }
+        }
+    }
+
+    /// Create from pre-lowered dependencies (for non-workspace contexts).
+    pub fn from_lowered(extra_build_dependencies: ExtraBuildDependencies) -> Self {
+        Self {
+            extra_build_dependencies,
+        }
+    }
+}

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

@@ -11,7 +11,7 @@ use uv_pypi_types::{HashDigests, ResolutionMetadata};
 use uv_workspace::dependency_groups::DependencyGroupError;
 use uv_workspace::{WorkspaceCache, WorkspaceError};
 
-pub use crate::metadata::build_requires::BuildRequires;
+pub use crate::metadata::build_requires::{BuildRequires, ExtraBuildRequires};
 pub use crate::metadata::dependency_groups::SourcedDependencyGroups;
 pub use crate::metadata::lowering::LoweredRequirement;
 pub use crate::metadata::lowering::LoweringError;