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 https://github.com/astral-sh/uv/issues/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> {
@@ -402,15 +405,21 @@ 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(
+        // 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(),
+        };
 
-        // Setup the build environment.
+        // 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,
@@ -422,7 +431,10 @@ impl SourceBuild {
             build_context
                 .install(&resolved_requirements, &venv)
                 .await
-            .map_err(|err| Error::RequirementsInstall("build-system.requires (install)", err))?;
+                .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
@@ -454,6 +466,9 @@ impl SourceBuild {
             OsString::from(venv.scripts())
         };
 
+        // 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,
@@ -468,6 +483,7 @@ impl SourceBuild {
                 )
                 .await?;
             }
+        }
 
         Ok(Self {
             temp_dir,

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() {
+            if !reinstalls.is_empty() {
-                for dist_info in extraneous.iter().chain(reinstalls.iter()) {
+                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 {
+    pub fn from_interpreter(interpreter: Interpreter) -> Self {
-        Self { root, interpreter }
+        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))
-    Ok(PythonEnvironment::from_interpreter(interpreter, root))
 }

crates/uv/src/commands/pip_compile.rs

@@ -24,13 +24,13 @@ use uv_client::{Connectivity, FlatIndex, FlatIndexClient, RegistryClientBuilder}
 use uv_dispatch::BuildDispatch;
 use uv_fs::Simplified;
 use uv_installer::{Downloader, NoBinary};
-use uv_interpreter::{Interpreter, PythonVersion};
+use uv_interpreter::{Interpreter, PythonEnvironment, PythonVersion};
 use uv_normalize::{ExtraName, PackageName};
 use uv_resolver::{
     AnnotationStyle, DependencyMode, DisplayResolutionGraph, InMemoryIndex, Manifest,
     OptionsBuilder, PreReleaseMode, PythonRequirement, ResolutionMode, Resolver,
 };
-use uv_traits::{ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
+use uv_traits::{BuildIsolation, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
 use uv_warnings::warn_user;
 
 use crate::commands::reporters::{DownloadReporter, ResolverReporter};
@@ -62,6 +62,7 @@ pub(crate) async fn pip_compile(
     setup_py: SetupPyStrategy,
     config_settings: ConfigSettings,
     connectivity: Connectivity,
+    no_build_isolation: bool,
     no_build: &NoBuild,
     python_version: Option<PythonVersion>,
     exclude_newer: Option<DateTime<Utc>>,
@@ -137,6 +138,7 @@ pub(crate) async fn pip_compile(
         interpreter.python_version(),
         interpreter.sys_executable().simplified_display().cyan()
     );
+
     if let Some(python_version) = python_version.as_ref() {
         // If the requested version does not match the version we're using warn the user
         // _unless_ they have not specified a patch version and that is the only difference
@@ -203,6 +205,15 @@ pub(crate) async fn pip_compile(
     // Track in-flight downloads, builds, etc., across resolutions.
     let in_flight = InFlight::default();
 
+    // Determine whether to enable build isolation.
+    let venv;
+    let build_isolation = if no_build_isolation {
+        venv = PythonEnvironment::from_interpreter(interpreter.clone());
+        BuildIsolation::Shared(&venv)
+    } else {
+        BuildIsolation::Isolated
+    };
+
     let build_dispatch = BuildDispatch::new(
         &client,
         &cache,
@@ -213,6 +224,7 @@ pub(crate) async fn pip_compile(
         &in_flight,
         setup_py,
         &config_settings,
+        build_isolation,
         no_build,
         &NoBinary::None,
     )

crates/uv/src/commands/pip_install.rs

@@ -32,7 +32,7 @@ use uv_resolver::{
     DependencyMode, InMemoryIndex, Manifest, Options, OptionsBuilder, PreReleaseMode,
     ResolutionGraph, ResolutionMode, Resolver,
 };
-use uv_traits::{ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
+use uv_traits::{BuildIsolation, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
 
 use crate::commands::reporters::{DownloadReporter, InstallReporter, ResolverReporter};
 use crate::commands::{compile_bytecode, elapsed, ChangeEvent, ChangeEventKind, ExitStatus};
@@ -59,6 +59,7 @@ pub(crate) async fn pip_install(
     setup_py: SetupPyStrategy,
     connectivity: Connectivity,
     config_settings: &ConfigSettings,
+    no_build_isolation: bool,
     no_build: &NoBuild,
     no_binary: &NoBinary,
     strict: bool,
@@ -190,6 +191,13 @@ pub(crate) async fn pip_install(
         FlatIndex::from_entries(entries, tags)
     };
 
+    // Determine whether to enable build isolation.
+    let build_isolation = if no_build_isolation {
+        BuildIsolation::Shared(&venv)
+    } else {
+        BuildIsolation::Isolated
+    };
+
     // Create a shared in-memory index.
     let index = InMemoryIndex::default();
 
@@ -206,6 +214,7 @@ pub(crate) async fn pip_install(
         &in_flight,
         setup_py,
         config_settings,
+        build_isolation,
         no_build,
         no_binary,
     )
@@ -289,6 +298,7 @@ pub(crate) async fn pip_install(
             &in_flight,
             setup_py,
             config_settings,
+            build_isolation,
             no_build,
             no_binary,
         )

crates/uv/src/commands/pip_sync.rs

@@ -20,7 +20,7 @@ use uv_installer::{
 };
 use uv_interpreter::{Interpreter, PythonEnvironment};
 use uv_resolver::InMemoryIndex;
-use uv_traits::{ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
+use uv_traits::{BuildIsolation, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
 
 use crate::commands::reporters::{DownloadReporter, FinderReporter, InstallReporter};
 use crate::commands::{compile_bytecode, elapsed, ChangeEvent, ChangeEventKind, ExitStatus};
@@ -38,6 +38,7 @@ pub(crate) async fn pip_sync(
     setup_py: SetupPyStrategy,
     connectivity: Connectivity,
     config_settings: &ConfigSettings,
+    no_build_isolation: bool,
     no_build: &NoBuild,
     no_binary: &NoBinary,
     strict: bool,
@@ -135,6 +136,13 @@ pub(crate) async fn pip_sync(
     // Track in-flight downloads, builds, etc., across resolutions.
     let in_flight = InFlight::default();
 
+    // Determine whether to enable build isolation.
+    let build_isolation = if no_build_isolation {
+        BuildIsolation::Shared(&venv)
+    } else {
+        BuildIsolation::Isolated
+    };
+
     // Prep the build context.
     let build_dispatch = BuildDispatch::new(
         &client,
@@ -146,6 +154,7 @@ pub(crate) async fn pip_sync(
         &in_flight,
         setup_py,
         config_settings,
+        build_isolation,
         no_build,
         no_binary,
     );

crates/uv/src/commands/venv.rs

@@ -21,7 +21,7 @@ use uv_fs::Simplified;
 use uv_installer::NoBinary;
 use uv_interpreter::{find_default_python, find_requested_python, Error};
 use uv_resolver::{InMemoryIndex, OptionsBuilder};
-use uv_traits::{BuildContext, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
+use uv_traits::{BuildContext, BuildIsolation, ConfigSettings, InFlight, NoBuild, SetupPyStrategy};
 
 use crate::commands::ExitStatus;
 use crate::printer::Printer;
@@ -172,6 +172,7 @@ async fn venv_impl(
             &in_flight,
             SetupPyStrategy::default(),
             &config_settings,
+            BuildIsolation::Isolated,
             &NoBuild::All,
             &NoBinary::None,
         )

crates/uv/src/compat/mod.rs

@@ -30,9 +30,6 @@ pub(crate) struct PipCompileCompatArgs {
     #[clap(long, hide = true)]
     build_isolation: bool,
 
-    #[clap(long, hide = true)]
-    no_build_isolation: bool,
-
     #[clap(long, hide = true)]
     resolver: Option<Resolver>,
 
@@ -117,12 +114,6 @@ impl CompatArgs for PipCompileCompatArgs {
             );
         }
 
-        if self.no_build_isolation {
-            return Err(anyhow!(
-                "pip-compile's `--no-build-isolation` is unsupported (uv always uses build isolation)."
-            ));
-        }
-
         if let Some(resolver) = self.resolver {
             match resolver {
                 Resolver::Backtracking => {

crates/uv/src/main.rs

@@ -370,6 +370,12 @@ struct PipCompileArgs {
     #[clap(long)]
     legacy_setup_py: bool,
 
+    /// Disable isolation when building source distributions.
+    ///
+    /// Assumes that build dependencies specified by PEP 518 are already installed.
+    #[clap(long)]
+    no_build_isolation: bool,
+
     /// Don't build source distributions.
     ///
     /// When enabled, resolving will not run arbitrary code. The cached wheels of already-built
@@ -550,6 +556,12 @@ struct PipSyncArgs {
     #[clap(long)]
     legacy_setup_py: bool,
 
+    /// Disable isolation when building source distributions.
+    ///
+    /// Assumes that build dependencies specified by PEP 518 are already installed.
+    #[clap(long)]
+    no_build_isolation: bool,
+
     /// Don't build source distributions.
     ///
     /// When enabled, resolving will not run arbitrary code. The cached wheels of already-built
@@ -790,6 +802,12 @@ struct PipInstallArgs {
     #[clap(long)]
     legacy_setup_py: bool,
 
+    /// Disable isolation when building source distributions.
+    ///
+    /// Assumes that build dependencies specified by PEP 518 are already installed.
+    #[clap(long)]
+    no_build_isolation: bool,
+
     /// Don't build source distributions.
     ///
     /// When enabled, resolving will not run arbitrary code. The cached wheels of already-built
@@ -1358,6 +1376,7 @@ async fn run() -> Result<ExitStatus> {
                 } else {
                     Connectivity::Online
                 },
+                args.no_build_isolation,
                 &no_build,
                 args.python_version,
                 args.exclude_newer,
@@ -1411,6 +1430,7 @@ async fn run() -> Result<ExitStatus> {
                     Connectivity::Online
                 },
                 &config_settings,
+                args.no_build_isolation,
                 &no_build,
                 &no_binary,
                 args.strict,
@@ -1504,6 +1524,7 @@ async fn run() -> Result<ExitStatus> {
                     Connectivity::Online
                 },
                 &config_settings,
+                args.no_build_isolation,
                 &no_build,
                 &no_binary,
                 args.strict,

crates/uv/tests/pip_install.rs

@@ -2348,3 +2348,74 @@ requires-python = "<=3.8"
 
     Ok(())
 }
+
+/// Install with `--no-build-isolation`, to disable isolation during PEP 517 builds.
+#[test]
+fn no_build_isolation() -> Result<()> {
+    let context = TestContext::new("3.12");
+    let requirements_in = context.temp_dir.child("requirements.in");
+    requirements_in.write_str("anyio @ https://files.pythonhosted.org/packages/db/4d/3970183622f0330d3c23d9b8a5f52e365e50381fd484d08e3285104333d3/anyio-4.3.0.tar.gz")?;
+
+    // We expect the build to fail, because `setuptools` is not installed.
+    let filters = std::iter::once((r"exit code: 1", "exit status: 1"))
+        .chain(INSTA_FILTERS.to_vec())
+        .collect::<Vec<_>>();
+    uv_snapshot!(filters, command(&context)
+        .arg("-r")
+        .arg("requirements.in")
+        .arg("--no-build-isolation"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Failed to download and build: anyio @ https://files.pythonhosted.org/packages/db/4d/3970183622f0330d3c23d9b8a5f52e365e50381fd484d08e3285104333d3/anyio-4.3.0.tar.gz
+      Caused by: Failed to build: anyio @ https://files.pythonhosted.org/packages/db/4d/3970183622f0330d3c23d9b8a5f52e365e50381fd484d08e3285104333d3/anyio-4.3.0.tar.gz
+      Caused by: Build backend failed to determine metadata through `prepare_metadata_for_build_wheel` with exit status: 1
+    --- stdout:
+
+    --- stderr:
+    Traceback (most recent call last):
+      File "<string>", line 8, in <module>
+    ModuleNotFoundError: No module named 'setuptools'
+    ---
+    "###
+    );
+
+    // Install `setuptools` and `wheel`.
+    uv_snapshot!(command(&context)
+        .arg("setuptools")
+        .arg("wheel"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 2 packages in [TIME]
+    Downloaded 2 packages in [TIME]
+    Installed 2 packages in [TIME]
+     + setuptools==68.2.2
+     + wheel==0.41.3
+    "###);
+
+    // We expect the build to succeed, since `setuptools` is now installed.
+    uv_snapshot!(command(&context)
+        .arg("-r")
+        .arg("requirements.in")
+        .arg("--no-build-isolation"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    Downloaded 3 packages in [TIME]
+    Installed 3 packages in [TIME]
+     + anyio==0.0.0 (from https://files.pythonhosted.org/packages/db/4d/3970183622f0330d3c23d9b8a5f52e365e50381fd484d08e3285104333d3/anyio-4.3.0.tar.gz)
+     + idna==3.4
+     + sniffio==1.3.0
+    "###
+    );
+
+    Ok(())
+}