Remove `--legacy-setup-py` command-line argument (#4255)

This is a fallback mode that we supported when we decided to use PEP 517
builds by default. I can't find a single reference to it on GitHub or in
our issue tracker, so I want to drop support for it as part of v0.3.0.

crates/bench/benches/uv.rs

@@ -91,7 +91,7 @@ mod resolver {
     use uv_cache::Cache;
     use uv_client::RegistryClient;
     use uv_configuration::{
-        BuildOptions, Concurrency, ConfigSettings, IndexStrategy, SetupPyStrategy, SourceStrategy,
+        BuildOptions, Concurrency, ConfigSettings, IndexStrategy, SourceStrategy,
     };
     use uv_dispatch::BuildDispatch;
     use uv_distribution::DistributionDatabase;
@@ -179,7 +179,6 @@ mod resolver {
             &git,
             &in_flight,
             IndexStrategy::default(),
-            SetupPyStrategy::default(),
             &config_settings,
             build_isolation,
             LinkMode::default(),

crates/uv-build/src/lib.rs

@@ -28,7 +28,7 @@ use distribution_types::Resolution;
 use pep440_rs::Version;
 use pep508_rs::PackageName;
 use pypi_types::{Requirement, VerbatimParsedUrl};
-use uv_configuration::{BuildKind, ConfigSettings, SetupPyStrategy};
+use uv_configuration::{BuildKind, ConfigSettings};
 use uv_fs::{rename_with_retry, PythonExt, Simplified};
 use uv_python::{Interpreter, PythonEnvironment};
 use uv_types::{BuildContext, BuildIsolation, SourceBuildTrait};
@@ -75,14 +75,6 @@ static DEFAULT_BACKEND: LazyLock<Pep517Backend> = LazyLock::new(|| Pep517Backend
     )],
 });
 
-/// The requirements for `--legacy-setup-py` builds.
-static SETUP_PY_REQUIREMENTS: LazyLock<[Requirement; 2]> = LazyLock::new(|| {
-    [
-        Requirement::from(pep508_rs::Requirement::from_str("setuptools >= 40.8.0").unwrap()),
-        Requirement::from(pep508_rs::Requirement::from_str("wheel").unwrap()),
-    ]
-});
-
 #[derive(Error, Debug)]
 pub enum Error {
     #[error(transparent)]
@@ -359,8 +351,6 @@ impl Pep517Backend {
 pub struct SourceBuildContext {
     /// An in-memory resolution of the default backend's requirements for PEP 517 builds.
     default_resolution: Rc<Mutex<Option<Resolution>>>,
-    /// An in-memory resolution of the build requirements for `--legacy-setup-py` builds.
-    setup_py_resolution: Rc<Mutex<Option<Resolution>>>,
 }
 
 /// Holds the state through a series of PEP 517 frontend to backend calls or a single setup.py
@@ -373,7 +363,7 @@ pub struct SourceBuild {
     source_tree: PathBuf,
     config_settings: ConfigSettings,
     /// If performing a PEP 517 build, the backend to use.
-    pep517_backend: Option<Pep517Backend>,
+    pep517_backend: Pep517Backend,
     /// The PEP 621 project metadata, if any.
     project: Option<Project>,
     /// The virtual environment in which to build the source distribution.
@@ -412,7 +402,6 @@ impl SourceBuild {
         build_context: &impl BuildContext,
         source_build_context: SourceBuildContext,
         version_id: String,
-        setup_py: SetupPyStrategy,
         config_settings: ConfigSettings,
         build_isolation: BuildIsolation<'_>,
         build_kind: BuildKind,
@@ -431,8 +420,7 @@ impl SourceBuild {
 
         // Check if we have a PEP 517 build backend.
         let (pep517_backend, project) =
-            Self::extract_pep517_backend(&source_tree, setup_py, &default_backend)
+            Self::extract_pep517_backend(&source_tree, &default_backend).map_err(|err| *err)?;
-                .map_err(|err| *err)?;
 
         let package_name = project.clone().map(|p| p.name);
 
@@ -457,7 +445,7 @@ impl SourceBuild {
                 build_context,
                 source_build_context,
                 &default_backend,
-                pep517_backend.as_ref(),
+                &pep517_backend,
             )
             .await?;
 
@@ -503,22 +491,20 @@ impl SourceBuild {
         // environment is already setup.
         let runner = PythonRunner::new(concurrent_builds);
         if build_isolation.is_isolated(package_name.as_ref()) {
-            if let Some(pep517_backend) = &pep517_backend {
+            create_pep517_build_environment(
-                create_pep517_build_environment(
+                &runner,
-                    &runner,
+                &source_tree,
-                    &source_tree,
+                &venv,
-                    &venv,
+                &pep517_backend,
-                    pep517_backend,
+                build_context,
-                    build_context,
+                &version_id,
-                    &version_id,
+                build_kind,
-                    build_kind,
+                &config_settings,
-                    &config_settings,
+                &environment_variables,
-                    &environment_variables,
+                &modified_path,
-                    &modified_path,
+                &temp_dir,
-                    &temp_dir,
+            )
-                )
+            .await?;
-                .await?;
-            }
         }
 
         Ok(Self {
@@ -541,9 +527,9 @@ impl SourceBuild {
         build_context: &impl BuildContext,
         source_build_context: SourceBuildContext,
         default_backend: &Pep517Backend,
-        pep517_backend: Option<&Pep517Backend>,
+        pep517_backend: &Pep517Backend,
     ) -> Result<Resolution, Error> {
-        Ok(if let Some(pep517_backend) = pep517_backend {
+        Ok(
             if pep517_backend.requirements == default_backend.requirements {
                 let mut resolution = source_build_context.default_resolution.lock().await;
                 if let Some(resolved_requirements) = &*resolution {
@@ -565,29 +551,15 @@ impl SourceBuild {
                     .map_err(|err| {
                         Error::RequirementsInstall("build-system.requires (resolve)", err)
                     })?
-            }
+            },
-        } else {
+        )
-            // Install default requirements for `setup.py`-based builds.
-            let mut resolution = source_build_context.setup_py_resolution.lock().await;
-            if let Some(resolved_requirements) = &*resolution {
-                resolved_requirements.clone()
-            } else {
-                let resolved_requirements = build_context
-                    .resolve(&*SETUP_PY_REQUIREMENTS)
-                    .await
-                    .map_err(|err| Error::RequirementsInstall("setup.py build (resolve)", err))?;
-                *resolution = Some(resolved_requirements.clone());
-                resolved_requirements
-            }
-        })
     }
 
     /// Extract the PEP 517 backend from the `pyproject.toml` or `setup.py` file.
     fn extract_pep517_backend(
         source_tree: &Path,
-        setup_py: SetupPyStrategy,
         default_backend: &Pep517Backend,
-    ) -> Result<(Option<Pep517Backend>, Option<Project>), Box<Error>> {
+    ) -> Result<(Pep517Backend, Option<Project>), Box<Error>> {
         match fs::read_to_string(source_tree.join("pyproject.toml")) {
             Ok(toml) => {
                 let pyproject_toml: PyProjectToml =
@@ -616,7 +588,7 @@ impl SourceBuild {
                     // a PEP 517 build using the default backend, to match `pip` and `build`.
                     default_backend.clone()
                 };
-                Ok((Some(backend), pyproject_toml.project))
+                Ok((backend, pyproject_toml.project))
             }
             Err(err) if err.kind() == io::ErrorKind::NotFound => {
                 // We require either a `pyproject.toml` or a `setup.py` file at the top level.
@@ -629,13 +601,9 @@ impl SourceBuild {
 
                 // If no `pyproject.toml` is present, by default, proceed with a PEP 517 build using
                 // the default backend, to match `build`. `pip` uses `setup.py` directly in this
-                // case (which we allow via `SetupPyStrategy::Setuptools`), but plans to make PEP
+                // case,  but plans to make PEP 517 builds the default in the future.
-                // 517 builds the default in the future.
                 // See: https://github.com/pypa/pip/issues/9175.
-                match setup_py {
+                Ok((default_backend.clone(), None))
-                    SetupPyStrategy::Pep517 => Ok((Some(default_backend.clone()), None)),
-                    SetupPyStrategy::Setuptools => Ok((None, None)),
-                }
             }
             Err(err) => Err(Box::new(err.into())),
         }
@@ -644,10 +612,6 @@ impl SourceBuild {
     /// Try calling `prepare_metadata_for_build_wheel` to get the metadata without executing the
     /// actual build.
     pub async fn get_metadata_without_build(&mut self) -> Result<Option<PathBuf>, Error> {
-        let Some(pep517_backend) = &self.pep517_backend else {
-            return Ok(None);
-        };
-
         // We've already called this method; return the existing result.
         if let Some(metadata_dir) = &self.metadata_directory {
             return Ok(Some(metadata_dir.clone()));
@@ -668,7 +632,7 @@ impl SourceBuild {
         // this is just an optimization.
         //
         // See: https://github.com/astral-sh/uv/issues/2130
-        if pep517_backend.backend == "hatchling.build" {
+        if self.pep517_backend.backend == "hatchling.build" {
             if self
                 .project
                 .as_ref()
@@ -694,7 +658,7 @@ impl SourceBuild {
 
         debug!(
             "Calling `{}.prepare_metadata_for_build_{}()`",
-            pep517_backend.backend, self.build_kind,
+            self.pep517_backend.backend, self.build_kind,
         );
         let script = formatdoc! {
             r#"
@@ -710,7 +674,7 @@ impl SourceBuild {
             with open("{}", "w") as fp:
                 fp.write(dirname or "")
             "#,
-            pep517_backend.backend_import(),
+            self.pep517_backend.backend_import(),
             self.build_kind,
             escape_path_for_python(&metadata_directory),
             self.config_settings.escape_for_python(),
@@ -760,55 +724,16 @@ impl SourceBuild {
         // The build scripts run with the extracted root as cwd, so they need the absolute path.
         let wheel_dir = fs::canonicalize(wheel_dir)?;
 
-        if let Some(pep517_backend) = &self.pep517_backend {
+        // Prevent clashes from two uv processes building wheels in parallel.
-            // Prevent clashes from two uv processes building wheels in parallel.
+        let tmp_dir = tempdir_in(&wheel_dir)?;
-            let tmp_dir = tempdir_in(&wheel_dir)?;
+        let filename = self
-            let filename = self.pep517_build(tmp_dir.path(), pep517_backend).await?;
+            .pep517_build(tmp_dir.path(), &self.pep517_backend)
+            .await?;
 
-            let from = tmp_dir.path().join(&filename);
+        let from = tmp_dir.path().join(&filename);
-            let to = wheel_dir.join(&filename);
+        let to = wheel_dir.join(&filename);
-            rename_with_retry(from, to).await?;
+        rename_with_retry(from, to).await?;
-            Ok(filename)
+        Ok(filename)
-        } else {
-            if self.build_kind != BuildKind::Wheel {
-                return Err(Error::EditableSetupPy);
-            }
-            // We checked earlier that setup.py exists.
-            let span = info_span!(
-                "run_python_script",
-                script="setup.py bdist_wheel",
-                python_version = %self.venv.interpreter().python_version()
-            );
-            let output = self
-                .runner
-                .run_setup_py(&self.venv, "bdist_wheel", &self.source_tree)
-                .instrument(span)
-                .await?;
-            if !output.status.success() {
-                return Err(Error::from_command_output(
-                    "Failed building wheel through setup.py".to_string(),
-                    &output,
-                    &self.version_id,
-                ));
-            }
-            let dist = fs::read_dir(self.source_tree.join("dist"))?;
-            let dist_dir = dist.collect::<io::Result<Vec<fs_err::DirEntry>>>()?;
-            let [dist_wheel] = dist_dir.as_slice() else {
-                return Err(Error::from_command_output(
-                    format!(
-                        "Expected exactly wheel in `dist/` after invoking setup.py, found {dist_dir:?}"
-                    ),
-                    &output,
-                    &self.version_id)
-                );
-            };
-
-            let from = dist_wheel.path();
-            let to = wheel_dir.join(dist_wheel.file_name());
-            fs_err::copy(from, to)?;
-
-            Ok(dist_wheel.file_name().to_string_lossy().to_string())
-        }
     }
 
     async fn pep517_build(
@@ -1072,28 +997,6 @@ impl PythonRunner {
             .await
             .map_err(|err| Error::CommandFailed(venv.python_executable().to_path_buf(), err))
     }
-
-    /// Spawn a process that runs a `setup.py` script.
-    ///
-    /// If the concurrency limit has been reached this method will wait until a pending
-    /// script completes before spawning this one.
-    ///
-    /// Note: It is the caller's responsibility to create an informative span.
-    async fn run_setup_py(
-        &self,
-        venv: &PythonEnvironment,
-        script: &str,
-        source_tree: &Path,
-    ) -> Result<Output, Error> {
-        let _permit = self.control.acquire().await.unwrap();
-
-        Command::new(venv.python_executable())
-            .args(["setup.py", script])
-            .current_dir(source_tree.simplified())
-            .output()
-            .await
-            .map_err(|err| Error::CommandFailed(venv.python_executable().to_path_buf(), err))
-    }
 }
 
 #[cfg(test)]

crates/uv-cli/src/lib.rs

@@ -869,14 +869,6 @@ pub struct PipCompileArgs {
     #[arg(long, overrides_with("generate_hashes"), hide = true)]
     pub no_generate_hashes: bool,
 
-    /// Use legacy `setuptools` behavior when building source distributions without a
-    /// `pyproject.toml`.
-    #[arg(long, overrides_with("no_legacy_setup_py"))]
-    pub legacy_setup_py: bool,
-
-    #[arg(long, overrides_with("legacy_setup_py"), hide = true)]
-    pub no_legacy_setup_py: bool,
-
     /// Don't build source distributions.
     ///
     /// When enabled, resolving will not run arbitrary Python code. The cached wheels of
@@ -1159,14 +1151,6 @@ pub struct PipSyncArgs {
     #[arg(long, conflicts_with = "target")]
     pub prefix: Option<PathBuf>,
 
-    /// Use legacy `setuptools` behavior when building source distributions without a
-    /// `pyproject.toml`.
-    #[arg(long, overrides_with("no_legacy_setup_py"))]
-    pub legacy_setup_py: bool,
-
-    #[arg(long, overrides_with("legacy_setup_py"), hide = true)]
-    pub no_legacy_setup_py: bool,
-
     /// Don't build source distributions.
     ///
     /// When enabled, resolving will not run arbitrary Python code. The cached wheels of
@@ -1449,14 +1433,6 @@ pub struct PipInstallArgs {
     #[arg(long, conflicts_with = "target")]
     pub prefix: Option<PathBuf>,
 
-    /// Use legacy `setuptools` behavior when building source distributions without a
-    /// `pyproject.toml`.
-    #[arg(long, overrides_with("no_legacy_setup_py"))]
-    pub legacy_setup_py: bool,
-
-    #[arg(long, overrides_with("legacy_setup_py"), hide = true)]
-    pub no_legacy_setup_py: bool,
-
     /// Don't build source distributions.
     ///
     /// When enabled, resolving will not run arbitrary Python code. The cached wheels of

crates/uv-configuration/src/build_options.rs

@@ -4,16 +4,6 @@ use pep508_rs::PackageName;
 
 use crate::{PackageNameSpecifier, PackageNameSpecifiers};
 
-/// The strategy to use when building source distributions that lack a `pyproject.toml`.
-#[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
-pub enum SetupPyStrategy {
-    /// Perform a PEP 517 build.
-    #[default]
-    Pep517,
-    /// Perform a build by invoking `setuptools` directly.
-    Setuptools,
-}
-
 #[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
 pub enum BuildKind {
     /// A regular PEP 517 wheel build

crates/uv-dev/src/build.rs

@@ -11,8 +11,7 @@ use uv_build::{SourceBuild, SourceBuildContext};
 use uv_cache::{Cache, CacheArgs};
 use uv_client::RegistryClientBuilder;
 use uv_configuration::{
-    BuildKind, BuildOptions, Concurrency, ConfigSettings, IndexStrategy, SetupPyStrategy,
+    BuildKind, BuildOptions, Concurrency, ConfigSettings, IndexStrategy, SourceStrategy,
-    SourceStrategy,
 };
 use uv_dispatch::BuildDispatch;
 use uv_git::GitResolver;
@@ -67,7 +66,6 @@ pub(crate) async fn build(args: BuildArgs) -> Result<PathBuf> {
     let index = InMemoryIndex::default();
     let index_urls = IndexLocations::default();
     let index_strategy = IndexStrategy::default();
-    let setup_py = SetupPyStrategy::default();
     let sources = SourceStrategy::default();
     let python = PythonEnvironment::find(
         &PythonRequest::default(),
@@ -88,7 +86,6 @@ pub(crate) async fn build(args: BuildArgs) -> Result<PathBuf> {
         &git,
         &in_flight,
         index_strategy,
-        setup_py,
         &config_settings,
         BuildIsolation::Isolated,
         install_wheel_rs::linker::LinkMode::default(),
@@ -105,7 +102,6 @@ pub(crate) async fn build(args: BuildArgs) -> Result<PathBuf> {
         &build_dispatch,
         SourceBuildContext::default(),
         args.sdist.display().to_string(),
-        setup_py,
         config_settings.clone(),
         BuildIsolation::Isolated,
         build_kind,

crates/uv-dispatch/src/lib.rs

@@ -18,8 +18,7 @@ use uv_cache::Cache;
 use uv_client::RegistryClient;
 use uv_configuration::Concurrency;
 use uv_configuration::{
-    BuildKind, BuildOptions, ConfigSettings, Constraints, IndexStrategy, Reinstall,
+    BuildKind, BuildOptions, ConfigSettings, Constraints, IndexStrategy, Reinstall, SourceStrategy,
-    SetupPyStrategy, SourceStrategy,
 };
 use uv_distribution::DistributionDatabase;
 use uv_git::GitResolver;
@@ -44,7 +43,6 @@ pub struct BuildDispatch<'a> {
     index: &'a InMemoryIndex,
     git: &'a GitResolver,
     in_flight: &'a InFlight,
-    setup_py: SetupPyStrategy,
     build_isolation: BuildIsolation<'a>,
     link_mode: install_wheel_rs::linker::LinkMode,
     build_options: &'a BuildOptions,
@@ -68,7 +66,6 @@ impl<'a> BuildDispatch<'a> {
         git: &'a GitResolver,
         in_flight: &'a InFlight,
         index_strategy: IndexStrategy,
-        setup_py: SetupPyStrategy,
         config_settings: &'a ConfigSettings,
         build_isolation: BuildIsolation<'a>,
         link_mode: install_wheel_rs::linker::LinkMode,
@@ -88,7 +85,6 @@ impl<'a> BuildDispatch<'a> {
             git,
             in_flight,
             index_strategy,
-            setup_py,
             config_settings,
             build_isolation,
             link_mode,
@@ -326,7 +322,6 @@ impl<'a> BuildContext for BuildDispatch<'a> {
             self,
             self.source_build_context.clone(),
             version_id.to_string(),
-            self.setup_py,
             self.config_settings.clone(),
             self.build_isolation,
             build_kind,

crates/uv-settings/src/settings.rs

@@ -948,16 +948,6 @@ pub struct PipOptions {
         "#
     )]
     pub generate_hashes: Option<bool>,
-    /// Use legacy `setuptools` behavior when building source distributions without a
-    /// `pyproject.toml`.
-    #[option(
-        default = "false",
-        value_type = "bool",
-        example = r#"
-            legacy-setup-py = true
-        "#
-    )]
-    pub legacy_setup_py: Option<bool>,
     /// Settings to pass to the [PEP 517](https://peps.python.org/pep-0517/) build backend,
     /// specified as `KEY=VALUE` pairs.
     #[option(

crates/uv/src/commands/pip/compile.rs

@@ -16,7 +16,7 @@ use uv_cache::Cache;
 use uv_client::{BaseClientBuilder, Connectivity, FlatIndexClient, RegistryClientBuilder};
 use uv_configuration::{
     BuildOptions, Concurrency, ConfigSettings, ExtrasSpecification, IndexStrategy, NoBinary,
-    NoBuild, Reinstall, SetupPyStrategy, SourceStrategy, Upgrade,
+    NoBuild, Reinstall, SourceStrategy, Upgrade,
 };
 use uv_configuration::{KeyringProviderType, TargetTriple};
 use uv_dispatch::BuildDispatch;
@@ -73,7 +73,6 @@ pub(crate) async fn pip_compile(
     index_locations: IndexLocations,
     index_strategy: IndexStrategy,
     keyring_provider: KeyringProviderType,
-    setup_py: SetupPyStrategy,
     config_settings: ConfigSettings,
     connectivity: Connectivity,
     no_build_isolation: bool,
@@ -322,7 +321,6 @@ pub(crate) async fn pip_compile(
         &git,
         &in_flight,
         index_strategy,
-        setup_py,
         &config_settings,
         build_isolation,
         link_mode,

crates/uv/src/commands/pip/install.rs

@@ -14,7 +14,7 @@ use uv_cache::Cache;
 use uv_client::{BaseClientBuilder, Connectivity, FlatIndexClient, RegistryClientBuilder};
 use uv_configuration::{
     BuildOptions, Concurrency, ConfigSettings, ExtrasSpecification, HashCheckingMode,
-    IndexStrategy, Reinstall, SetupPyStrategy, SourceStrategy, Upgrade,
+    IndexStrategy, Reinstall, SourceStrategy, Upgrade,
 };
 use uv_configuration::{KeyringProviderType, TargetTriple};
 use uv_dispatch::BuildDispatch;
@@ -57,7 +57,6 @@ pub(crate) async fn pip_install(
     link_mode: LinkMode,
     compile: bool,
     hash_checking: Option<HashCheckingMode>,
-    setup_py: SetupPyStrategy,
     connectivity: Connectivity,
     config_settings: &ConfigSettings,
     no_build_isolation: bool,
@@ -312,7 +311,6 @@ pub(crate) async fn pip_install(
         &state.git,
         &state.in_flight,
         index_strategy,
-        setup_py,
         config_settings,
         build_isolation,
         link_mode,

crates/uv/src/commands/pip/sync.rs

@@ -13,7 +13,7 @@ use uv_cache::Cache;
 use uv_client::{BaseClientBuilder, Connectivity, FlatIndexClient, RegistryClientBuilder};
 use uv_configuration::{
     BuildOptions, Concurrency, ConfigSettings, ExtrasSpecification, HashCheckingMode,
-    IndexStrategy, Reinstall, SetupPyStrategy, SourceStrategy, Upgrade,
+    IndexStrategy, Reinstall, SourceStrategy, Upgrade,
 };
 use uv_configuration::{KeyringProviderType, TargetTriple};
 use uv_dispatch::BuildDispatch;
@@ -48,7 +48,6 @@ pub(crate) async fn pip_sync(
     index_locations: IndexLocations,
     index_strategy: IndexStrategy,
     keyring_provider: KeyringProviderType,
-    setup_py: SetupPyStrategy,
     allow_empty_requirements: bool,
     connectivity: Connectivity,
     config_settings: &ConfigSettings,
@@ -258,7 +257,6 @@ pub(crate) async fn pip_sync(
         &state.git,
         &state.in_flight,
         index_strategy,
-        setup_py,
         config_settings,
         build_isolation,
         link_mode,

crates/uv/src/commands/project/add.rs

@@ -11,7 +11,7 @@ use tracing::debug;
 use uv_auth::{store_credentials_from_url, Credentials};
 use uv_cache::Cache;
 use uv_client::{BaseClientBuilder, Connectivity, FlatIndexClient, RegistryClientBuilder};
-use uv_configuration::{Concurrency, ExtrasSpecification, SetupPyStrategy, SourceStrategy};
+use uv_configuration::{Concurrency, ExtrasSpecification, SourceStrategy};
 use uv_dispatch::BuildDispatch;
 use uv_distribution::DistributionDatabase;
 use uv_fs::{Simplified, CWD};
@@ -234,7 +234,6 @@ pub(crate) async fn add(
     let python_version = None;
     let python_platform = None;
     let hasher = HashStrategy::default();
-    let setup_py = SetupPyStrategy::default();
     let build_isolation = BuildIsolation::default();
 
     // Determine the environment for the resolution.
@@ -279,7 +278,6 @@ pub(crate) async fn add(
         &state.git,
         &state.in_flight,
         settings.index_strategy,
-        setup_py,
         &settings.config_setting,
         build_isolation,
         settings.link_mode,

crates/uv/src/commands/project/lock.rs

@@ -14,7 +14,7 @@ use pypi_types::Requirement;
 use uv_auth::store_credentials_from_url;
 use uv_cache::Cache;
 use uv_client::{Connectivity, FlatIndexClient, RegistryClientBuilder};
-use uv_configuration::{Concurrency, ExtrasSpecification, Reinstall, SetupPyStrategy, Upgrade};
+use uv_configuration::{Concurrency, ExtrasSpecification, Reinstall, Upgrade};
 use uv_dispatch::BuildDispatch;
 use uv_distribution::DistributionDatabase;
 use uv_fs::CWD;
@@ -383,7 +383,6 @@ async fn do_lock(
     // optional on the downstream APIs.
     let build_constraints = [];
     let extras = ExtrasSpecification::default();
-    let setup_py = SetupPyStrategy::default();
 
     // Resolve the flat indexes from `--find-links`.
     let flat_index = {
@@ -404,7 +403,6 @@ async fn do_lock(
         &state.git,
         &state.in_flight,
         index_strategy,
-        setup_py,
         config_setting,
         build_isolation,
         link_mode,

crates/uv/src/commands/project/mod.rs

@@ -11,7 +11,7 @@ use pypi_types::Requirement;
 use uv_auth::store_credentials_from_url;
 use uv_cache::Cache;
 use uv_client::{BaseClientBuilder, Connectivity, FlatIndexClient, RegistryClientBuilder};
-use uv_configuration::{Concurrency, ExtrasSpecification, Reinstall, SetupPyStrategy, Upgrade};
+use uv_configuration::{Concurrency, ExtrasSpecification, Reinstall, Upgrade};
 use uv_dispatch::BuildDispatch;
 use uv_distribution::DistributionDatabase;
 use uv_fs::Simplified;
@@ -451,7 +451,6 @@ pub(crate) async fn resolve_names(
     // TODO(charlie): These are all default values. We should consider whether we want to make them
     // optional on the downstream APIs.
     let hasher = HashStrategy::default();
-    let setup_py = SetupPyStrategy::default();
     let flat_index = FlatIndex::default();
     let build_constraints = [];
 
@@ -467,7 +466,6 @@ pub(crate) async fn resolve_names(
         &state.git,
         &state.in_flight,
         *index_strategy,
-        setup_py,
         config_setting,
         build_isolation,
         *link_mode,
@@ -576,7 +574,6 @@ pub(crate) async fn resolve_environment<'a>(
     let extras = ExtrasSpecification::default();
     let hasher = HashStrategy::default();
     let preferences = Vec::default();
-    let setup_py = SetupPyStrategy::default();
     let build_constraints = [];
 
     // When resolving from an interpreter, we assume an empty environment, so reinstalls and
@@ -603,7 +600,6 @@ pub(crate) async fn resolve_environment<'a>(
         &state.git,
         &state.in_flight,
         index_strategy,
-        setup_py,
         config_setting,
         build_isolation,
         link_mode,
@@ -705,7 +701,6 @@ pub(crate) async fn sync_environment(
     let build_constraints = [];
     let dry_run = false;
     let hasher = HashStrategy::default();
-    let setup_py = SetupPyStrategy::default();
 
     // Resolve the flat indexes from `--find-links`.
     let flat_index = {
@@ -726,7 +721,6 @@ pub(crate) async fn sync_environment(
         &state.git,
         &state.in_flight,
         index_strategy,
-        setup_py,
         config_setting,
         build_isolation,
         link_mode,
@@ -899,7 +893,6 @@ pub(crate) async fn update_environment(
     let extras = ExtrasSpecification::default();
     let hasher = HashStrategy::default();
     let preferences = Vec::default();
-    let setup_py = SetupPyStrategy::default();
 
     // Resolve the flat indexes from `--find-links`.
     let flat_index = {
@@ -920,7 +913,6 @@ pub(crate) async fn update_environment(
         &state.git,
         &state.in_flight,
         *index_strategy,
-        setup_py,
         config_setting,
         build_isolation,
         *link_mode,

crates/uv/src/commands/project/sync.rs

@@ -4,7 +4,7 @@ use pep508_rs::MarkerTree;
 use uv_auth::store_credentials_from_url;
 use uv_cache::Cache;
 use uv_client::{Connectivity, FlatIndexClient, RegistryClientBuilder};
-use uv_configuration::{Concurrency, ExtrasSpecification, HashCheckingMode, SetupPyStrategy};
+use uv_configuration::{Concurrency, ExtrasSpecification, HashCheckingMode};
 use uv_dispatch::BuildDispatch;
 use uv_fs::CWD;
 use uv_installer::SitePackages;
@@ -216,7 +216,6 @@ pub(super) async fn do_sync(
     // optional on the downstream APIs.
     let build_constraints = [];
     let dry_run = false;
-    let setup_py = SetupPyStrategy::default();
 
     // Extract the hashes from the lockfile.
     let hasher = HashStrategy::from_resolution(&resolution, HashCheckingMode::Verify)?;
@@ -240,7 +239,6 @@ pub(super) async fn do_sync(
         &state.git,
         &state.in_flight,
         index_strategy,
-        setup_py,
         config_setting,
         build_isolation,
         link_mode,

crates/uv/src/commands/venv.rs

@@ -17,7 +17,7 @@ use uv_cache::Cache;
 use uv_client::{BaseClientBuilder, Connectivity, FlatIndexClient, RegistryClientBuilder};
 use uv_configuration::{
     BuildOptions, Concurrency, ConfigSettings, IndexStrategy, KeyringProviderType, NoBinary,
-    NoBuild, SetupPyStrategy, SourceStrategy,
+    NoBuild, SourceStrategy,
 };
 use uv_dispatch::BuildDispatch;
 use uv_fs::{Simplified, CWD};
@@ -274,7 +274,6 @@ async fn venv_impl(
         // For seed packages, assume a bunch of default settings are sufficient.
         let build_constraints = [];
         let config_settings = ConfigSettings::default();
-        let setup_py = SetupPyStrategy::default();
         let sources = SourceStrategy::Disabled;
 
         // Do not allow builds
@@ -292,7 +291,6 @@ async fn venv_impl(
             &state.git,
             &state.in_flight,
             index_strategy,
-            setup_py,
             &config_settings,
             BuildIsolation::Isolated,
             link_mode,

crates/uv/src/lib.rs

@@ -306,7 +306,6 @@ async fn run(cli: Cli) -> Result<ExitStatus> {
                 args.settings.index_locations,
                 args.settings.index_strategy,
                 args.settings.keyring_provider,
-                args.settings.setup_py,
                 args.settings.config_setting,
                 globals.connectivity,
                 args.settings.no_build_isolation,
@@ -373,7 +372,6 @@ async fn run(cli: Cli) -> Result<ExitStatus> {
                 args.settings.index_locations,
                 args.settings.index_strategy,
                 args.settings.keyring_provider,
-                args.settings.setup_py,
                 args.settings.allow_empty_requirements,
                 globals.connectivity,
                 &args.settings.config_setting,
@@ -461,7 +459,6 @@ async fn run(cli: Cli) -> Result<ExitStatus> {
                 args.settings.link_mode,
                 args.settings.compile_bytecode,
                 args.settings.hash_checking,
-                args.settings.setup_py,
                 globals.connectivity,
                 &args.settings.config_setting,
                 args.settings.no_build_isolation,

crates/uv/src/settings.rs

@@ -23,8 +23,8 @@ use uv_cli::{
 use uv_client::Connectivity;
 use uv_configuration::{
     BuildOptions, Concurrency, ConfigSettings, ExtrasSpecification, HashCheckingMode,
-    IndexStrategy, KeyringProviderType, NoBinary, NoBuild, PreviewMode, Reinstall, SetupPyStrategy,
+    IndexStrategy, KeyringProviderType, NoBinary, NoBuild, PreviewMode, Reinstall, SourceStrategy,
-    SourceStrategy, TargetTriple, Upgrade,
+    TargetTriple, Upgrade,
 };
 use uv_normalize::PackageName;
 use uv_python::{Prefix, PythonDownloads, PythonPreference, PythonVersion, Target};
@@ -937,8 +937,6 @@ impl PipCompileSettings {
             no_system,
             generate_hashes,
             no_generate_hashes,
-            legacy_setup_py,
-            no_legacy_setup_py,
             no_build,
             build,
             no_binary,
@@ -1023,7 +1021,6 @@ impl PipCompileSettings {
                     no_header: flag(no_header, header),
                     custom_compile_command,
                     generate_hashes: flag(generate_hashes, no_generate_hashes),
-                    legacy_setup_py: flag(legacy_setup_py, no_legacy_setup_py),
                     python_version,
                     python_platform,
                     universal: flag(universal, no_universal),
@@ -1076,8 +1073,6 @@ impl PipSyncSettings {
             prefix,
             allow_empty_requirements,
             no_allow_empty_requirements,
-            legacy_setup_py,
-            no_legacy_setup_py,
             no_build,
             build,
             no_binary,
@@ -1118,7 +1113,6 @@ impl PipSyncSettings {
                         allow_empty_requirements,
                         no_allow_empty_requirements,
                     ),
-                    legacy_setup_py: flag(legacy_setup_py, no_legacy_setup_py),
                     python_version,
                     python_platform,
                     strict: flag(strict, no_strict),
@@ -1175,8 +1169,6 @@ impl PipInstallSettings {
             no_break_system_packages,
             target,
             prefix,
-            legacy_setup_py,
-            no_legacy_setup_py,
             no_build,
             build,
             no_binary,
@@ -1251,7 +1243,6 @@ impl PipInstallSettings {
                     extra,
                     all_extras: flag(all_extras, no_all_extras),
                     no_deps: flag(no_deps, deps),
-                    legacy_setup_py: flag(legacy_setup_py, no_legacy_setup_py),
                     python_version,
                     python_platform,
                     require_hashes: flag(require_hashes, no_require_hashes),
@@ -1839,7 +1830,6 @@ pub(crate) struct PipSettings {
     pub(crate) no_header: bool,
     pub(crate) custom_compile_command: Option<String>,
     pub(crate) generate_hashes: bool,
-    pub(crate) setup_py: SetupPyStrategy,
     pub(crate) config_setting: ConfigSettings,
     pub(crate) python_version: Option<PythonVersion>,
     pub(crate) python_platform: Option<TargetTriple>,
@@ -1898,7 +1888,6 @@ impl PipSettings {
             no_header,
             custom_compile_command,
             generate_hashes,
-            legacy_setup_py,
             config_settings,
             python_version,
             python_platform,
@@ -2025,15 +2014,6 @@ impl PipSettings {
                 .allow_empty_requirements
                 .combine(allow_empty_requirements)
                 .unwrap_or_default(),
-            setup_py: if args
-                .legacy_setup_py
-                .combine(legacy_setup_py)
-                .unwrap_or_default()
-            {
-                SetupPyStrategy::Setuptools
-            } else {
-                SetupPyStrategy::Pep517
-            },
             no_build_isolation: args
                 .no_build_isolation
                 .combine(no_build_isolation)

crates/uv/tests/pip_compile.rs

@@ -4119,7 +4119,7 @@ fn trailing_slash() -> Result<()> {
     Ok(())
 }
 
-/// Resolve a project without a `pyproject.toml`, using the PEP 517 build backend (default).
+/// Resolve a project without a `pyproject.toml`, using the PEP 517 build backend.
 #[test]
 fn compile_legacy_sdist_pep_517() -> Result<()> {
     let context = TestContext::new("3.12");
@@ -4150,38 +4150,6 @@ fn compile_legacy_sdist_pep_517() -> Result<()> {
     Ok(())
 }
 
-/// Resolve a project without a `pyproject.toml`, using `setuptools` directly.
-#[test]
-fn compile_legacy_sdist_setuptools() -> Result<()> {
-    let context = TestContext::new("3.12");
-    let requirements_in = context.temp_dir.child("requirements.in");
-    requirements_in.write_str("flake8 @ https://files.pythonhosted.org/packages/66/53/3ad4a3b74d609b3b9008a10075c40e7c8909eae60af53623c3888f7a529a/flake8-6.0.0.tar.gz")?;
-
-    uv_snapshot!(context.filters(), context.pip_compile()
-            .arg("requirements.in")
-            .arg("--legacy-setup-py"), @r###"
-    success: true
-    exit_code: 0
-    ----- stdout -----
-    # This file was autogenerated by uv via the following command:
-    #    uv pip compile --cache-dir [CACHE_DIR] requirements.in --legacy-setup-py
-    flake8 @ https://files.pythonhosted.org/packages/66/53/3ad4a3b74d609b3b9008a10075c40e7c8909eae60af53623c3888f7a529a/flake8-6.0.0.tar.gz
-        # via -r requirements.in
-    mccabe==0.7.0
-        # via flake8
-    pycodestyle==2.10.0
-        # via flake8
-    pyflakes==3.0.1
-        # via flake8
-
-    ----- stderr -----
-    Resolved 4 packages in [TIME]
-    "###
-    );
-
-    Ok(())
-}
-
 /// Include hashes from the registry in the generated output.
 #[test]
 fn generate_hashes_registry() -> Result<()> {

crates/uv/tests/pip_sync.rs

@@ -2610,7 +2610,7 @@ fn incompatible_wheel() -> Result<()> {
     Ok(())
 }
 
-/// Install a project without a `pyproject.toml`, using the PEP 517 build backend (default).
+/// Install a project without a `pyproject.toml`, using the PEP 517 build backend.
 #[test]
 fn sync_legacy_sdist_pep_517() -> Result<()> {
     let context = TestContext::new("3.12");
@@ -2635,32 +2635,6 @@ fn sync_legacy_sdist_pep_517() -> Result<()> {
     Ok(())
 }
 
-/// Install a project without a `pyproject.toml`, using `setuptools` directly.
-#[test]
-fn sync_legacy_sdist_setuptools() -> Result<()> {
-    let context = TestContext::new("3.12");
-
-    let requirements_in = context.temp_dir.child("requirements.in");
-    requirements_in.write_str("flake8 @ https://files.pythonhosted.org/packages/66/53/3ad4a3b74d609b3b9008a10075c40e7c8909eae60af53623c3888f7a529a/flake8-6.0.0.tar.gz")?;
-
-    uv_snapshot!(context.pip_sync()
-        .arg("requirements.in")
-        .arg("--legacy-setup-py"), @r###"
-    success: true
-    exit_code: 0
-    ----- stdout -----
-
-    ----- stderr -----
-    Resolved 1 package in [TIME]
-    Prepared 1 package in [TIME]
-    Installed 1 package in [TIME]
-     + flake8==6.0.0 (from https://files.pythonhosted.org/packages/66/53/3ad4a3b74d609b3b9008a10075c40e7c8909eae60af53623c3888f7a529a/flake8-6.0.0.tar.gz)
-    "###
-    );
-
-    Ok(())
-}
-
 /// Sync using `--find-links` with a local directory.
 #[test]
 fn find_links() -> Result<()> {

crates/uv/tests/show_settings.rs

@@ -143,7 +143,6 @@ fn resolve_uv_toml() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: true,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -279,7 +278,6 @@ fn resolve_uv_toml() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: true,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -416,7 +414,6 @@ fn resolve_uv_toml() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -585,7 +582,6 @@ fn resolve_pyproject_toml() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: true,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -700,7 +696,6 @@ fn resolve_pyproject_toml() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -847,7 +842,6 @@ fn resolve_pyproject_toml() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: true,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -1031,7 +1025,6 @@ fn resolve_index_url() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -1214,7 +1207,6 @@ fn resolve_index_url() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -1375,7 +1367,6 @@ fn resolve_find_links() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -1512,7 +1503,6 @@ fn resolve_top_level() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -1687,7 +1677,6 @@ fn resolve_top_level() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -1845,7 +1834,6 @@ fn resolve_top_level() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -1982,7 +1970,6 @@ fn resolve_user_configuration() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -2102,7 +2089,6 @@ fn resolve_user_configuration() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: true,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -2222,7 +2208,6 @@ fn resolve_user_configuration() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -2344,7 +2329,6 @@ fn resolve_user_configuration() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -2636,7 +2620,6 @@ fn resolve_poetry_toml() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -2807,7 +2790,6 @@ fn resolve_both() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: true,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -2970,7 +2952,6 @@ fn resolve_config_file() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: true,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -3185,7 +3166,6 @@ fn resolve_skip_empty() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),
@@ -3308,7 +3288,6 @@ fn resolve_skip_empty() -> anyhow::Result<()> {
             no_header: false,
             custom_compile_command: None,
             generate_hashes: false,
-            setup_py: Pep517,
             config_setting: ConfigSettings(
                 {},
             ),

docs/reference/cli.md

@@ -3678,8 +3678,6 @@ uv pip compile [OPTIONS] <SRC_FILE>...
 
 <li><code>subprocess</code>:  Use the <code>keyring</code> command for credential lookup</li>
 </ul>
-</dd><dt><code>--legacy-setup-py</code></dt><dd><p>Use legacy <code>setuptools</code> behavior when building source distributions without a <code>pyproject.toml</code></p>
-
 </dd><dt><code>--link-mode</code> <i>link-mode</i></dt><dd><p>The method to use when installing packages from the global cache.</p>
 
 <p>This option is only used when building source distributions.</p>
@@ -4021,8 +4019,6 @@ uv pip sync [OPTIONS] <SRC_FILE>...
 
 <li><code>subprocess</code>:  Use the <code>keyring</code> command for credential lookup</li>
 </ul>
-</dd><dt><code>--legacy-setup-py</code></dt><dd><p>Use legacy <code>setuptools</code> behavior when building source distributions without a <code>pyproject.toml</code></p>
-
 </dd><dt><code>--link-mode</code> <i>link-mode</i></dt><dd><p>The method to use when installing packages from the global cache.</p>
 
 <p>Defaults to <code>clone</code> (also known as Copy-on-Write) on macOS, and <code>hardlink</code> on Linux and Windows.</p>
@@ -4320,8 +4316,6 @@ uv pip install [OPTIONS] <PACKAGE|--requirement <REQUIREMENT>|--editable <EDITAB
 
 <li><code>subprocess</code>:  Use the <code>keyring</code> command for credential lookup</li>
 </ul>
-</dd><dt><code>--legacy-setup-py</code></dt><dd><p>Use legacy <code>setuptools</code> behavior when building source distributions without a <code>pyproject.toml</code></p>
-
 </dd><dt><code>--link-mode</code> <i>link-mode</i></dt><dd><p>The method to use when installing packages from the global cache.</p>
 
 <p>Defaults to <code>clone</code> (also known as Copy-on-Write) on macOS, and <code>hardlink</code> on Linux and Windows.</p>

docs/reference/settings.md

@@ -1625,33 +1625,6 @@ use the `keyring` CLI to handle authentication.
 
 ---
 
-#### [`legacy-setup-py`](#pip_legacy-setup-py) {: #pip_legacy-setup-py }
-<span id="legacy-setup-py"></span>
-
-Use legacy `setuptools` behavior when building source distributions without a
-`pyproject.toml`.
-
-**Default value**: `false`
-
-**Type**: `bool`
-
-**Example usage**:
-
-=== "pyproject.toml"
-
-    ```toml
-    [tool.uv.pip]
-    legacy-setup-py = true
-    ```
-=== "uv.toml"
-
-    ```toml
-    [pip]
-    legacy-setup-py = true
-    ```
-
----
-
 #### [`link-mode`](#pip_link-mode) {: #pip_link-mode }
 <span id="link-mode"></span>
 

uv.schema.json

@@ -721,13 +721,6 @@
             }
           ]
         },
-        "legacy-setup-py": {
-          "description": "Use legacy `setuptools` behavior when building source distributions without a `pyproject.toml`.",
-          "type": [
-            "boolean",
-            "null"
-          ]
-        },
         "link-mode": {
           "description": "The method to use when installing packages from the global cache.\n\nDefaults to `clone` (also known as Copy-on-Write) on macOS, and `hardlink` on Linux and Windows.",
           "anyOf": [