Move warnings for conflicting modules into preview

crates/uv-configuration/src/preview.rs

@@ -16,6 +16,7 @@ bitflags::bitflags! {
         const ADD_BOUNDS = 1 << 4;
         const PACKAGE_CONFLICTS = 1 << 5;
         const EXTRA_BUILD_DEPENDENCIES = 1 << 6;
+        const DETECT_MODULE_CONFLICTS = 1 << 7;
     }
 }
 
@@ -32,6 +33,7 @@ impl PreviewFeatures {
             Self::ADD_BOUNDS => "add-bounds",
             Self::PACKAGE_CONFLICTS => "package-conflicts",
             Self::EXTRA_BUILD_DEPENDENCIES => "extra-build-dependencies",
+            Self::DETECT_MODULE_CONFLICTS => "detect-module-conflicts",
             _ => panic!("`flag_as_str` can only be used for exactly one feature flag"),
         }
     }
@@ -76,6 +78,7 @@ impl FromStr for PreviewFeatures {
                 "add-bounds" => Self::ADD_BOUNDS,
                 "package-conflicts" => Self::PACKAGE_CONFLICTS,
                 "extra-build-dependencies" => Self::EXTRA_BUILD_DEPENDENCIES,
+                "detect-module-conflicts" => Self::DETECT_MODULE_CONFLICTS,
                 _ => {
                     warn_user_once!("Unknown preview feature: `{part}`");
                     continue;
@@ -246,6 +249,10 @@ mod tests {
             PreviewFeatures::EXTRA_BUILD_DEPENDENCIES.flag_as_str(),
             "extra-build-dependencies"
         );
+        assert_eq!(
+            PreviewFeatures::DETECT_MODULE_CONFLICTS.flag_as_str(),
+            "detect-module-conflicts"
+        );
     }
 
     #[test]

crates/uv-dispatch/src/lib.rs

@@ -390,7 +390,7 @@ impl BuildContext for BuildDispatch<'_> {
                 if wheels.len() == 1 { "" } else { "s" },
                 wheels.iter().map(ToString::to_string).join(", ")
             );
-            wheels = Installer::new(venv)
+            wheels = Installer::new(venv, self.preview)
                 .with_link_mode(self.link_mode)
                 .with_cache(self.cache)
                 .install(wheels)

crates/uv-install-wheel/Cargo.toml

@@ -22,6 +22,7 @@ name = "uv_install_wheel"
 
 [dependencies]
 uv-cache-info = { workspace = true }
+uv-configuration = { workspace = true }
 uv-distribution-filename = { workspace = true }
 uv-fs = { workspace = true }
 uv-normalize = { workspace = true }

crates/uv-install-wheel/src/linker.rs

@@ -10,20 +10,33 @@ use std::sync::{Arc, Mutex};
 use std::time::SystemTime;
 use tempfile::tempdir_in;
 use tracing::{debug, instrument, trace};
+use uv_configuration::{Preview, PreviewFeatures};
 use uv_distribution_filename::WheelFilename;
 use uv_fs::Simplified;
 use uv_warnings::{warn_user, warn_user_once};
 use walkdir::WalkDir;
 
+#[allow(clippy::struct_field_names)]
 #[derive(Debug, Default)]
 pub struct Locks {
     /// The parent directory of a file in a synchronized copy
     copy_dir_locks: Mutex<FxHashMap<PathBuf, Arc<Mutex<()>>>>,
     /// Top level modules (excluding namespaces) we write to.
     modules: Mutex<FxHashMap<OsString, WheelFilename>>,
+    /// Preview settings for feature flags.
+    preview: Preview,
 }
 
 impl Locks {
+    /// Create a new Locks instance with the given preview settings.
+    pub fn new(preview: Preview) -> Self {
+        Self {
+            copy_dir_locks: Mutex::new(FxHashMap::default()),
+            modules: Mutex::new(FxHashMap::default()),
+            preview,
+        }
+    }
+
     /// Warn when a module exists in multiple packages.
     fn warn_module_conflict(&self, module: &OsStr, wheel_a: &WheelFilename) {
         if let Some(wheel_b) = self
@@ -32,6 +45,14 @@ impl Locks {
             .unwrap()
             .insert(module.to_os_string(), wheel_a.clone())
         {
+            // Only warn if the preview feature is enabled
+            if !self
+                .preview
+                .is_enabled(PreviewFeatures::DETECT_MODULE_CONFLICTS)
+            {
+                return;
+            }
+
             // Sort for consistent output, at least with two packages
             let (wheel_a, wheel_b) = if wheel_b.name > wheel_a.name {
                 (&wheel_b, wheel_a)

crates/uv-installer/src/installer.rs

@@ -7,7 +7,7 @@ use tokio::sync::oneshot;
 use tracing::instrument;
 
 use uv_cache::Cache;
-use uv_configuration::RAYON_INITIALIZE;
+use uv_configuration::{Preview, RAYON_INITIALIZE};
 use uv_distribution_types::CachedDist;
 use uv_install_wheel::{Layout, LinkMode};
 use uv_python::PythonEnvironment;
@@ -21,18 +21,21 @@ pub struct Installer<'a> {
     name: Option<String>,
     /// The metadata associated with the [`Installer`].
     metadata: bool,
+    /// Preview settings for the installer.
+    preview: Preview,
 }
 
 impl<'a> Installer<'a> {
     /// Initialize a new installer.
-    pub fn new(venv: &'a PythonEnvironment) -> Self {
+    pub fn new(venv: &'a PythonEnvironment, preview: Preview) -> Self {
         Self {
             venv,
             link_mode: LinkMode::default(),
             cache: None,
             reporter: None,
             name: Some("uv".to_string()),
             metadata: true,
+            preview,
         }
     }
 
@@ -88,6 +91,7 @@ impl<'a> Installer<'a> {
             reporter,
             name: installer_name,
             metadata: installer_metadata,
+            preview,
         } = self;
 
         if cache.is_some_and(Cache::is_temporary) {
@@ -113,6 +117,7 @@ impl<'a> Installer<'a> {
                 reporter.as_ref(),
                 relocatable,
                 installer_metadata,
+                preview,
             );
 
             // This may fail if the main task was cancelled.
@@ -143,6 +148,7 @@ impl<'a> Installer<'a> {
             self.reporter.as_ref(),
             self.venv.relocatable(),
             self.metadata,
+            self.preview,
         )
     }
 }
@@ -157,10 +163,11 @@ fn install(
     reporter: Option<&Arc<dyn Reporter>>,
     relocatable: bool,
     installer_metadata: bool,
+    preview: Preview,
 ) -> Result<Vec<CachedDist>> {
     // Initialize the threadpool with the user settings.
     LazyLock::force(&RAYON_INITIALIZE);
-    let locks = uv_install_wheel::Locks::default();
+    let locks = uv_install_wheel::Locks::new(preview);
     wheels.par_iter().try_for_each(|wheel| {
         uv_install_wheel::install_wheel(
             layout,

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

@@ -611,6 +611,7 @@ pub(crate) async fn pip_install(
         installer_metadata,
         dry_run,
         printer,
+        preview,
     )
     .await
     {

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

@@ -450,6 +450,7 @@ pub(crate) async fn install(
     installer_metadata: bool,
     dry_run: DryRun,
     printer: Printer,
+    preview: uv_configuration::Preview,
 ) -> Result<Changelog, Error> {
     let start = std::time::Instant::now();
 
@@ -571,7 +572,7 @@ pub(crate) async fn install(
     let mut installs = wheels.into_iter().chain(cached).collect::<Vec<_>>();
     if !installs.is_empty() {
         let start = std::time::Instant::now();
-        installs = uv_installer::Installer::new(venv)
+        installs = uv_installer::Installer::new(venv, preview)
             .with_link_mode(link_mode)
             .with_cache(cache)
             .with_installer_metadata(installer_metadata)

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

@@ -550,6 +550,7 @@ pub(crate) async fn pip_sync(
         installer_metadata,
         dry_run,
         printer,
+        preview,
     )
     .await
     {

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

@@ -2173,6 +2173,7 @@ pub(crate) async fn sync_environment(
         installer_metadata,
         dry_run,
         printer,
+        preview,
     )
     .await?;
 
@@ -2434,6 +2435,7 @@ pub(crate) async fn update_environment(
         installer_metadata,
         dry_run,
         printer,
+        preview,
     )
     .await?;
 

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

@@ -809,6 +809,7 @@ pub(super) async fn do_sync(
         installer_metadata,
         dry_run,
         printer,
+        preview,
     )
     .await?;
 

crates/uv/tests/it/pip_install.rs

@@ -12486,7 +12486,7 @@ fn overlapping_packages_warning() -> Result<()> {
         .child("__init__.py")
         .touch()?;
 
-    // Check that overlapping packages show a warning
+    // Check that overlapping packages don't show a warning by default
     uv_snapshot!(context.filters(), context.pip_install()
         .arg("--no-deps")
         .arg(&built_by_uv)
@@ -12495,6 +12495,29 @@ fn overlapping_packages_warning() -> Result<()> {
     exit_code: 0
     ----- stdout -----
 
+    ----- stderr -----
+    Resolved 2 packages in [TIME]
+    Prepared 2 packages in [TIME]
+    Installed 2 packages in [TIME]
+     + also-built-by-uv==0.1.0 (from file://[TEMP_DIR]/also-built-by-uv)
+     + built-by-uv==0.1.0 (from file://[WORKSPACE]/scripts/packages/built-by-uv)
+    "
+    );
+
+    // Clean up for the next test
+    context.venv().arg("--clear").assert().success();
+
+    // Check that overlapping packages show a warning when preview feature is enabled
+    uv_snapshot!(context.filters(), context.pip_install()
+        .arg("--no-deps")
+        .arg("--preview-features")
+        .arg("detect-module-conflicts")
+        .arg(&built_by_uv)
+        .arg(also_build_by_uv.path()), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
     ----- stderr -----
     Resolved 2 packages in [TIME]
     Prepared 2 packages in [TIME]

crates/uv/tests/it/show_settings.rs

@@ -7720,7 +7720,7 @@ fn preview_features() {
         show_settings: true,
         preview: Preview {
             flags: PreviewFeatures(
-                PYTHON_INSTALL_DEFAULT | PYTHON_UPGRADE | JSON_OUTPUT | PYLOCK | ADD_BOUNDS | PACKAGE_CONFLICTS | EXTRA_BUILD_DEPENDENCIES,
+                PYTHON_INSTALL_DEFAULT | PYTHON_UPGRADE | JSON_OUTPUT | PYLOCK | ADD_BOUNDS | PACKAGE_CONFLICTS | EXTRA_BUILD_DEPENDENCIES | DETECT_MODULE_CONFLICTS,
             ),
         },
         python_preference: Managed,
@@ -7946,7 +7946,7 @@ fn preview_features() {
         show_settings: true,
         preview: Preview {
             flags: PreviewFeatures(
-                PYTHON_INSTALL_DEFAULT | PYTHON_UPGRADE | JSON_OUTPUT | PYLOCK | ADD_BOUNDS | PACKAGE_CONFLICTS | EXTRA_BUILD_DEPENDENCIES,
+                PYTHON_INSTALL_DEFAULT | PYTHON_UPGRADE | JSON_OUTPUT | PYLOCK | ADD_BOUNDS | PACKAGE_CONFLICTS | EXTRA_BUILD_DEPENDENCIES | DETECT_MODULE_CONFLICTS,
             ),
         },
         python_preference: Managed,