Add support for --no-build-isolation (#2258)

## Summary

This PR adds support for pip's `--no-build-isolation`. When enabled,
build requirements won't be installed during PEP 517-style builds, but
the source environment _will_ be used when executing the build steps
themselves.

Closes #1715.

PIP_COMPATIBILITY.md

@@ -307,7 +307,6 @@ the implementation, and tend to be tracked in individual issues. For example:
 
 - [`--trusted-host`](https://github.com/astral-sh/uv/issues/1339)
 - [`--user`](https://github.com/astral-sh/uv/issues/2077)
-- [`--no-build-isolation`](https://github.com/astral-sh/uv/issues/1715)
 
 If you encounter a missing option or subcommand, please search the issue tracker to see if it has
 already been reported, and if not, consider opening a new issue. Feel free to upvote any existing

crates/uv-build/src/lib.rs

@@ -31,7 +31,9 @@ use distribution_types::Resolution;
 use pep508_rs::Requirement;
 use uv_fs::Simplified;
 use uv_interpreter::{Interpreter, PythonEnvironment};
-use uv_traits::{BuildContext, BuildKind, ConfigSettings, SetupPyStrategy, SourceBuildTrait};
+use uv_traits::{
+    BuildContext, BuildIsolation, BuildKind, ConfigSettings, SetupPyStrategy, SourceBuildTrait,
+};
 
 /// e.g. `pygraphviz/graphviz_wrap.c:3020:10: fatal error: graphviz/cgraph.h: No such file or directory`
 static MISSING_HEADER_RE: Lazy<Regex> = Lazy::new(|| {
@@ -357,6 +359,7 @@ impl SourceBuild {
         package_id: String,
         setup_py: SetupPyStrategy,
         config_settings: ConfigSettings,
+        build_isolation: BuildIsolation<'_>,
         build_kind: BuildKind,
         mut environment_variables: FxHashMap<OsString, OsString>,
     ) -> Result<Self, Error> {
@@ -402,27 +405,36 @@ impl SourceBuild {
         let pep517_backend = Self::get_pep517_backend(setup_py, &source_tree, &default_backend)
             .map_err(|err| *err)?;
 
-        let venv = uv_virtualenv::create_venv(
-            &temp_dir.path().join(".venv"),
-            interpreter.clone(),
-            uv_virtualenv::Prompt::None,
-            false,
-            Vec::new(),
-        )?;
-
-        // Setup the build environment.
-        let resolved_requirements = Self::get_resolved_requirements(
-            build_context,
-            source_build_context,
-            &default_backend,
-            pep517_backend.as_ref(),
-        )
-        .await?;
+        // Create a virtual environment, or install into the shared environment if requested.
+        let venv = match build_isolation {
+            BuildIsolation::Isolated => uv_virtualenv::create_venv(
+                &temp_dir.path().join(".venv"),
+                interpreter.clone(),
+                uv_virtualenv::Prompt::None,
+                false,
+                Vec::new(),
+            )?,
+            BuildIsolation::Shared(venv) => venv.clone(),
+        };
 
-        build_context
-            .install(&resolved_requirements, &venv)
-            .await
-            .map_err(|err| Error::RequirementsInstall("build-system.requires (install)", err))?;
+        // Setup the build environment. If build isolation is disabled, we assume the build
+        // environment is already setup.
+        if build_isolation.is_isolated() {
+            let resolved_requirements = Self::get_resolved_requirements(
+                build_context,
+                source_build_context,
+                &default_backend,
+                pep517_backend.as_ref(),
+            )
+            .await?;
+
+            build_context
+                .install(&resolved_requirements, &venv)
+                .await
+                .map_err(|err| {
+                    Error::RequirementsInstall("build-system.requires (install)", err)
+                })?;
+        }
 
         // Figure out what the modified path should be
         // Remove the PATH variable from the environment variables if it's there
@@ -454,19 +466,23 @@ impl SourceBuild {
             OsString::from(venv.scripts())
         };
 
-        if let Some(pep517_backend) = &pep517_backend {
-            create_pep517_build_environment(
-                &source_tree,
-                &venv,
-                pep517_backend,
-                build_context,
-                &package_id,
-                build_kind,
-                &config_settings,
-                &environment_variables,
-                &modified_path,
-            )
-            .await?;
+        // Create the PEP 517 build environment. If build isolation is disabled, we assume the build
+        // environment is already setup.
+        if build_isolation.is_isolated() {
+            if let Some(pep517_backend) = &pep517_backend {
+                create_pep517_build_environment(
+                    &source_tree,
+                    &venv,
+                    pep517_backend,
+                    build_context,
+                    &package_id,
+                    build_kind,
+                    &config_settings,
+                    &environment_variables,
+                    &modified_path,
+                )
+                .await?;
+            }
         }
 
         Ok(Self {

crates/uv-dev/src/build.rs

@@ -15,7 +15,9 @@ use uv_dispatch::BuildDispatch;
 use uv_installer::NoBinary;
 use uv_interpreter::PythonEnvironment;
 use uv_resolver::InMemoryIndex;
-use uv_traits::{BuildContext, BuildKind, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
+use uv_traits::{
+    BuildContext, BuildIsolation, BuildKind, ConfigSettings, InFlight, NoBuild, SetupPyStrategy,
+};
 
 #[derive(Parser)]
 pub(crate) struct BuildArgs {
@@ -74,6 +76,7 @@ pub(crate) async fn build(args: BuildArgs) -> Result<PathBuf> {
         &in_flight,
         setup_py,
         &config_settings,
+        BuildIsolation::Isolated,
         &NoBuild::None,
         &NoBinary::None,
     );
@@ -87,6 +90,7 @@ pub(crate) async fn build(args: BuildArgs) -> Result<PathBuf> {
         args.sdist.display().to_string(),
         setup_py,
         config_settings.clone(),
+        BuildIsolation::Isolated,
         build_kind,
         FxHashMap::default(),
     )

crates/uv-dev/src/install_many.rs

@@ -24,7 +24,7 @@ use uv_installer::{Downloader, NoBinary};
 use uv_interpreter::PythonEnvironment;
 use uv_normalize::PackageName;
 use uv_resolver::{DistFinder, InMemoryIndex};
-use uv_traits::{BuildContext, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
+use uv_traits::{BuildContext, BuildIsolation, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
 
 #[derive(Parser)]
 pub(crate) struct InstallManyArgs {
@@ -81,6 +81,7 @@ pub(crate) async fn install_many(args: InstallManyArgs) -> Result<()> {
         &in_flight,
         setup_py,
         &config_settings,
+        BuildIsolation::Isolated,
         &no_build,
         &NoBinary::None,
     );

crates/uv-dev/src/resolve_cli.rs

@@ -18,7 +18,7 @@ use uv_dispatch::BuildDispatch;
 use uv_installer::NoBinary;
 use uv_interpreter::PythonEnvironment;
 use uv_resolver::{InMemoryIndex, Manifest, Options, Resolver};
-use uv_traits::{ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
+use uv_traits::{BuildIsolation, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
 
 #[derive(ValueEnum, Default, Clone)]
 pub(crate) enum ResolveCliFormat {
@@ -85,6 +85,7 @@ pub(crate) async fn resolve_cli(args: ResolveCliArgs) -> Result<()> {
         &in_flight,
         SetupPyStrategy::default(),
         &config_settings,
+        BuildIsolation::Isolated,
         &no_build,
         &NoBinary::None,
     );

crates/uv-dev/src/resolve_many.rs

@@ -21,7 +21,7 @@ use uv_installer::NoBinary;
 use uv_interpreter::PythonEnvironment;
 use uv_normalize::PackageName;
 use uv_resolver::InMemoryIndex;
-use uv_traits::{BuildContext, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
+use uv_traits::{BuildContext, BuildIsolation, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
 
 #[derive(Parser)]
 pub(crate) struct ResolveManyArgs {
@@ -109,6 +109,7 @@ pub(crate) async fn resolve_many(args: ResolveManyArgs) -> Result<()> {
                     &in_flight,
                     setup_py,
                     &config_settings,
+                    BuildIsolation::Isolated,
                     &no_build,
                     &NoBinary::None,
                 );

crates/uv-dispatch/src/lib.rs

@@ -20,7 +20,9 @@ use uv_client::{FlatIndex, RegistryClient};
 use uv_installer::{Downloader, Installer, NoBinary, Plan, Planner, Reinstall, SitePackages};
 use uv_interpreter::{Interpreter, PythonEnvironment};
 use uv_resolver::{InMemoryIndex, Manifest, Options, Resolver};
-use uv_traits::{BuildContext, BuildKind, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
+use uv_traits::{
+    BuildContext, BuildIsolation, BuildKind, ConfigSettings, InFlight, NoBuild, SetupPyStrategy,
+};
 
 /// The main implementation of [`BuildContext`], used by the CLI, see [`BuildContext`]
 /// documentation.
@@ -33,6 +35,7 @@ pub struct BuildDispatch<'a> {
     index: &'a InMemoryIndex,
     in_flight: &'a InFlight,
     setup_py: SetupPyStrategy,
+    build_isolation: BuildIsolation<'a>,
     no_build: &'a NoBuild,
     no_binary: &'a NoBinary,
     config_settings: &'a ConfigSettings,
@@ -53,6 +56,7 @@ impl<'a> BuildDispatch<'a> {
         in_flight: &'a InFlight,
         setup_py: SetupPyStrategy,
         config_settings: &'a ConfigSettings,
+        build_isolation: BuildIsolation<'a>,
         no_build: &'a NoBuild,
         no_binary: &'a NoBinary,
     ) -> Self {
@@ -66,6 +70,7 @@ impl<'a> BuildDispatch<'a> {
             in_flight,
             setup_py,
             config_settings,
+            build_isolation,
             no_build,
             no_binary,
             source_build_context: SourceBuildContext::default(),
@@ -107,6 +112,10 @@ impl<'a> BuildContext for BuildDispatch<'a> {
         self.interpreter
     }
 
+    fn build_isolation(&self) -> BuildIsolation {
+        self.build_isolation
+    }
+
     fn no_build(&self) -> &NoBuild {
         self.no_build
     }
@@ -180,7 +189,7 @@ impl<'a> BuildContext for BuildDispatch<'a> {
                 local,
                 remote,
                 reinstalls,
-                extraneous,
+                extraneous: _,
             } = Planner::with_requirements(&resolution.requirements()).build(
                 site_packages,
                 &Reinstall::None,
@@ -191,6 +200,12 @@ impl<'a> BuildContext for BuildDispatch<'a> {
                 tags,
             )?;
 
+            // Nothing to do.
+            if remote.is_empty() && local.is_empty() && reinstalls.is_empty() {
+                debug!("No build requirements to install for build");
+                return Ok(());
+            }
+
             // Resolve any registry-based requirements.
             let remote = remote
                 .iter()
@@ -207,7 +222,7 @@ impl<'a> BuildContext for BuildDispatch<'a> {
                 vec![]
             } else {
                 // TODO(konstin): Check that there is no endless recursion.
-                let downloader = Downloader::new(self.cache(), tags, self.client, self);
+                let downloader = Downloader::new(self.cache, tags, self.client, self);
                 debug!(
                     "Downloading and building requirement{} for build: {}",
                     if remote.len() == 1 { "" } else { "s" },
@@ -221,8 +236,8 @@ impl<'a> BuildContext for BuildDispatch<'a> {
             };
 
             // Remove any unnecessary packages.
-            if !extraneous.is_empty() || !reinstalls.is_empty() {
-                for dist_info in extraneous.iter().chain(reinstalls.iter()) {
+            if !reinstalls.is_empty() {
+                for dist_info in &reinstalls {
                     let summary = uv_installer::uninstall(dist_info)
                         .await
                         .context("Failed to uninstall build dependencies")?;
@@ -295,6 +310,7 @@ impl<'a> BuildContext for BuildDispatch<'a> {
             package_id.to_string(),
             self.setup_py,
             self.config_settings.clone(),
+            self.build_isolation,
             build_kind,
             self.build_extra_env_vars.clone(),
         )

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

@@ -949,6 +949,8 @@ impl<'a, T: BuildContext> SourceDistCachedBuilder<'a, T> {
         editable_wheel_dir: &Path,
     ) -> Result<(Dist, String, WheelFilename, Metadata21), Error> {
         debug!("Building (editable) {editable}");
+
+        // Build the wheel.
         let disk_filename = self
             .build_context
             .setup_build(

crates/uv-interpreter/src/python_environment.rs

@@ -65,8 +65,11 @@ impl PythonEnvironment {
     }
 
     /// Create a [`PythonEnvironment`] from an existing [`Interpreter`] and root directory.
-    pub fn from_interpreter(interpreter: Interpreter, root: PathBuf) -> Self {
-        Self { root, interpreter }
+    pub fn from_interpreter(interpreter: Interpreter) -> Self {
+        Self {
+            root: interpreter.prefix().to_path_buf(),
+            interpreter,
+        }
     }
 
     /// Returns the location of the Python interpreter.
@@ -100,7 +103,7 @@ impl PythonEnvironment {
         self.interpreter.scripts()
     }
 
-    /// Lock the virtual environment to prevent concurrent writes.
+    /// Grab a file lock for the virtual environment to prevent concurrent writes across processes.
     pub fn lock(&self) -> Result<LockedFile, std::io::Error> {
         if self.interpreter.is_virtualenv() {
             // If the environment a virtualenv, use a virtualenv-specific lock file.

crates/uv-resolver/tests/resolver.rs

@@ -21,7 +21,9 @@ use uv_resolver::{
     DisplayResolutionGraph, InMemoryIndex, Manifest, Options, OptionsBuilder, PreReleaseMode,
     ResolutionGraph, ResolutionMode, Resolver,
 };
-use uv_traits::{BuildContext, BuildKind, NoBinary, NoBuild, SetupPyStrategy, SourceBuildTrait};
+use uv_traits::{
+    BuildContext, BuildIsolation, BuildKind, NoBinary, NoBuild, SetupPyStrategy, SourceBuildTrait,
+};
 
 // Exclude any packages uploaded after this date.
 static EXCLUDE_NEWER: Lazy<DateTime<Utc>> = Lazy::new(|| {
@@ -57,6 +59,10 @@ impl BuildContext for DummyContext {
         &self.interpreter
     }
 
+    fn build_isolation(&self) -> BuildIsolation {
+        BuildIsolation::Isolated
+    }
+
     fn no_build(&self) -> &NoBuild {
         &NoBuild::None
     }

crates/uv-traits/src/lib.rs

@@ -54,16 +54,19 @@ use uv_normalize::PackageName;
 /// `uv-build` to depend on `uv-resolver` which having actual crate dependencies between
 /// them.
 
-// TODO(konstin): Proper error types
 pub trait BuildContext: Sync {
     type SourceDistBuilder: SourceBuildTrait + Send + Sync;
 
+    /// Return a reference to the cache.
     fn cache(&self) -> &Cache;
 
     /// All (potentially nested) source distribution builds use the same base python and can reuse
     /// it's metadata (e.g. wheel compatibility tags).
     fn interpreter(&self) -> &Interpreter;
 
+    /// Whether to enforce build isolation when building source distributions.
+    fn build_isolation(&self) -> BuildIsolation;
+
     /// Whether source distribution building is disabled. This [`BuildContext::setup_build`] calls
     /// will fail in this case. This method exists to avoid fetching source distributions if we know
     /// we can't build them
@@ -137,6 +140,20 @@ pub struct InFlight {
     pub downloads: OnceMap<DistributionId, Result<CachedDist, String>>,
 }
 
+/// Whether to enforce build isolation when building source distributions.
+#[derive(Debug, Copy, Clone)]
+pub enum BuildIsolation<'a> {
+    Isolated,
+    Shared(&'a PythonEnvironment),
+}
+
+impl<'a> BuildIsolation<'a> {
+    /// Returns `true` if build isolation is enforced.
+    pub fn is_isolated(&self) -> bool {
+        matches!(self, Self::Isolated)
+    }
+}
+
 /// The strategy to use when building source distributions that lack a `pyproject.toml`.
 #[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
 pub enum SetupPyStrategy {

crates/uv-virtualenv/src/lib.rs

@@ -64,6 +64,5 @@ pub fn create_venv(
 
     // Create the corresponding `PythonEnvironment`.
     let interpreter = interpreter.with_virtualenv(virtualenv);
-    let root = interpreter.prefix().to_path_buf();
-    Ok(PythonEnvironment::from_interpreter(interpreter, root))
+    Ok(PythonEnvironment::from_interpreter(interpreter))
 }