Prefer system Python installations over managed ones when --system is used

Author: zanieb

crates/uv-dev/src/compile.rs

@@ -5,7 +5,7 @@ use tracing::info;
 
 use uv_cache::{Cache, CacheArgs};
 use uv_configuration::{Concurrency, Preview};
-use uv_python::{EnvironmentPreference, PythonEnvironment, PythonRequest};
+use uv_python::{EnvironmentPreference, PythonEnvironment, PythonPreference, PythonRequest};
 
 #[derive(Parser)]
 pub(crate) struct CompileArgs {
@@ -25,6 +25,7 @@ pub(crate) async fn compile(args: CompileArgs) -> anyhow::Result<()> {
         let interpreter = PythonEnvironment::find(
             &PythonRequest::default(),
             EnvironmentPreference::OnlyVirtual,
+            PythonPreference::default(),
             &cache,
             Preview::default(),
         )?

crates/uv-python/src/discovery.rs

@@ -2093,6 +2093,30 @@ impl PythonPreference {
             Self::Managed | Self::System | Self::OnlyManaged => true,
         }
     }
+
+    /// Returns a new preference when the `--system` flag is used.
+    ///
+    /// This will convert [`PythonPreference::Managed`] to [`PythonPreference::System`] when system
+    /// is set.
+    #[must_use]
+    pub fn with_system_flag(self, system: bool) -> Self {
+        match self {
+            // TODO(zanieb): It's not clear if we want to allow `--system` to override
+            // `--managed-python`. We should probably make this `from_system_flag` and refactor
+            // handling of the `PythonPreference` to use an `Option` so we can tell if the user
+            // provided it?
+            Self::OnlyManaged => self,
+            Self::Managed => {
+                if system {
+                    Self::System
+                } else {
+                    self
+                }
+            }
+            Self::System => self,
+            Self::OnlySystem => self,
+        }
+    }
 }
 
 impl PythonDownloads {

crates/uv-python/src/environment.rs

@@ -152,19 +152,16 @@ impl PythonEnvironment {
     pub fn find(
         request: &PythonRequest,
         preference: EnvironmentPreference,
+        python_preference: PythonPreference,
         cache: &Cache,
         preview: Preview,
     ) -> Result<Self, Error> {
-        let installation = match find_python_installation(
-            request,
-            preference,
-            PythonPreference::default(),
-            cache,
-            preview,
-        )? {
-            Ok(installation) => installation,
-            Err(err) => return Err(EnvironmentNotFound::from(err).into()),
-        };
+        let installation =
+            match find_python_installation(request, preference, python_preference, cache, preview)?
+            {
+                Ok(installation) => installation,
+                Err(err) => return Err(EnvironmentNotFound::from(err).into()),
+            };
         Ok(Self::from_installation(installation))
     }
 

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

@@ -8,6 +8,7 @@ use uv_cache::Cache;
 use uv_configuration::Preview;
 use uv_distribution_types::{Diagnostic, InstalledDist};
 use uv_installer::{SitePackages, SitePackagesDiagnostic};
+use uv_python::PythonPreference;
 use uv_python::{EnvironmentPreference, PythonEnvironment, PythonRequest};
 
 use crate::commands::pip::operations::report_target_environment;
@@ -28,6 +29,7 @@ pub(crate) fn pip_check(
     let environment = PythonEnvironment::find(
         &python.map(PythonRequest::parse).unwrap_or_default(),
         EnvironmentPreference::from_system_flag(system, false),
+        PythonPreference::default().with_system_flag(system),
         cache,
         preview,
     )?;

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

@@ -283,6 +283,7 @@ pub(crate) async fn pip_compile(
 
     // Find an interpreter to use for building distributions
     let environment_preference = EnvironmentPreference::from_system_flag(system, false);
+    let python_preference = python_preference.with_system_flag(system);
     let interpreter = if let Some(python) = python.as_ref() {
         let request = PythonRequest::parse(python);
         PythonInstallation::find(

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

@@ -9,6 +9,7 @@ use uv_cache::Cache;
 use uv_configuration::Preview;
 use uv_distribution_types::{Diagnostic, InstalledDist, Name};
 use uv_installer::SitePackages;
+use uv_python::PythonPreference;
 use uv_python::{EnvironmentPreference, PythonEnvironment, PythonRequest};
 
 use crate::commands::ExitStatus;
@@ -30,6 +31,7 @@ pub(crate) fn pip_freeze(
     let environment = PythonEnvironment::find(
         &python.map(PythonRequest::parse).unwrap_or_default(),
         EnvironmentPreference::from_system_flag(system, false),
+        PythonPreference::default().with_system_flag(system),
         cache,
         preview,
     )?;

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

@@ -193,7 +193,7 @@ pub(crate) async fn pip_install(
                 .map(PythonRequest::parse)
                 .unwrap_or_default(),
             EnvironmentPreference::from_system_flag(system, false),
-            python_preference,
+            python_preference.with_system_flag(system),
             &cache,
             preview,
         )?;
@@ -206,6 +206,7 @@ pub(crate) async fn pip_install(
                 .map(PythonRequest::parse)
                 .unwrap_or_default(),
             EnvironmentPreference::from_system_flag(system, true),
+            PythonPreference::default().with_system_flag(system),
             &cache,
             preview,
         )?;

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

@@ -25,7 +25,7 @@ use uv_installer::SitePackages;
 use uv_normalize::PackageName;
 use uv_pep440::Version;
 use uv_python::PythonRequest;
-use uv_python::{EnvironmentPreference, PythonEnvironment};
+use uv_python::{EnvironmentPreference, PythonEnvironment, PythonPreference};
 use uv_resolver::{ExcludeNewer, PrereleaseMode};
 
 use crate::commands::ExitStatus;
@@ -65,6 +65,7 @@ pub(crate) async fn pip_list(
     let environment = PythonEnvironment::find(
         &python.map(PythonRequest::parse).unwrap_or_default(),
         EnvironmentPreference::from_system_flag(system, false),
+        PythonPreference::default().with_system_flag(system),
         cache,
         preview,
     )?;

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

@@ -13,7 +13,7 @@ use uv_fs::Simplified;
 use uv_install_wheel::read_record_file;
 use uv_installer::SitePackages;
 use uv_normalize::PackageName;
-use uv_python::{EnvironmentPreference, PythonEnvironment, PythonRequest};
+use uv_python::{EnvironmentPreference, PythonEnvironment, PythonPreference, PythonRequest};
 
 use crate::commands::ExitStatus;
 use crate::commands::pip::operations::report_target_environment;
@@ -47,6 +47,7 @@ pub(crate) fn pip_show(
     let environment = PythonEnvironment::find(
         &python.map(PythonRequest::parse).unwrap_or_default(),
         EnvironmentPreference::from_system_flag(system, false),
+        PythonPreference::default().with_system_flag(system),
         cache,
         preview,
     )?;

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

@@ -170,7 +170,7 @@ pub(crate) async fn pip_sync(
                 .map(PythonRequest::parse)
                 .unwrap_or_default(),
             EnvironmentPreference::from_system_flag(system, false),
-            python_preference,
+            python_preference.with_system_flag(system),
             &cache,
             preview,
         )?;
@@ -183,6 +183,7 @@ pub(crate) async fn pip_sync(
                 .map(PythonRequest::parse)
                 .unwrap_or_default(),
             EnvironmentPreference::from_system_flag(system, true),
+            PythonPreference::default().with_system_flag(system),
             &cache,
             preview,
         )?;