Move preference behavior out of resolve (#3919)

## Summary

Decoupling this behavior to give more control to clients. No change in
behavior.

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

@@ -26,7 +26,7 @@ use uv_normalize::PackageName;
 use uv_requirements::{RequirementsSource, RequirementsSpecification};
 use uv_resolver::{
     DependencyMode, ExcludeNewer, FlatIndex, InMemoryIndex, Lock, OptionsBuilder, PreReleaseMode,
-    ResolutionMode,
+    Preference, ResolutionMode,
 };
 use uv_types::{BuildIsolation, HashStrategy, InFlight};
 
@@ -255,6 +255,12 @@ pub(crate) async fn pip_install(
         HashStrategy::None
     };
 
+    // When resolving, prefer current site packages.
+    let preferences = site_packages
+        .iter()
+        .map(Preference::from_installed)
+        .collect::<Vec<_>>();
+
     // Incorporate any index locations from the provided sources.
     let index_locations =
         index_locations.combine(index_url, extra_index_urls, find_links, no_index);
@@ -340,6 +346,7 @@ pub(crate) async fn pip_install(
             source_trees,
             project,
             extras,
+            preferences,
             site_packages.clone(),
             &hasher,
             &reinstall,

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

@@ -110,6 +110,7 @@ pub(crate) async fn resolve<InstalledPackages: InstalledPackagesProvider>(
     source_trees: Vec<PathBuf>,
     project: Option<PackageName>,
     extras: &ExtrasSpecification,
+    preferences: Vec<Preference>,
     installed_packages: InstalledPackages,
     hasher: &HashStrategy,
     reinstall: &Reinstall,
@@ -196,11 +197,10 @@ pub(crate) async fn resolve<InstalledPackages: InstalledPackagesProvider>(
     // TODO(zanieb): Consider consuming these instead of cloning
     let exclusions = Exclusions::new(reinstall.clone(), upgrade.clone());
 
-    // Prefer current site packages; filter out packages that are marked for reinstall or upgrade.
-    let preferences = installed_packages
-        .iter()
+    // Filter out any excluded distributions from the preferences.
+    let preferences = preferences
+        .into_iter()
         .filter(|dist| !exclusions.contains(dist.name()))
-        .map(Preference::from_installed)
         .collect::<Vec<_>>();
 
     // Create a manifest of the requirements.

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

@@ -24,7 +24,7 @@ use uv_interpreter::{PythonEnvironment, PythonVersion, SystemPython, Target};
 use uv_requirements::{RequirementsSource, RequirementsSpecification};
 use uv_resolver::{
     DependencyMode, ExcludeNewer, FlatIndex, InMemoryIndex, OptionsBuilder, PreReleaseMode,
-    ResolutionMode,
+    Preference, ResolutionMode,
 };
 use uv_types::{BuildIsolation, HashStrategy, InFlight};
 
@@ -275,6 +275,12 @@ pub(crate) async fn pip_sync(
     // Determine the set of installed packages.
     let site_packages = SitePackages::from_executable(&venv)?;
 
+    // When resolving, prefer current site packages.
+    let preferences = site_packages
+        .iter()
+        .map(Preference::from_installed)
+        .collect::<Vec<_>>();
+
     let options = OptionsBuilder::new()
         .resolution_mode(resolution_mode)
         .prerelease_mode(prerelease_mode)
@@ -290,6 +296,7 @@ pub(crate) async fn pip_sync(
         source_trees,
         project,
         &extras,
+        preferences,
         site_packages.clone(),
         &hasher,
         reinstall,

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

@@ -96,6 +96,7 @@ pub(super) async fn do_lock(
     let link_mode = LinkMode::default();
     let no_binary = NoBinary::default();
     let no_build = NoBuild::default();
+    let preferences = Vec::default();
     let reinstall = Reinstall::default();
     let setup_py = SetupPyStrategy::default();
     let upgrade = Upgrade::default();
@@ -129,6 +130,7 @@ pub(super) async fn do_lock(
         source_trees,
         Some(project_name),
         &extras,
+        preferences,
         EmptyInstalledPackages,
         &hasher,
         &reinstall,

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

@@ -169,7 +169,11 @@ pub(crate) async fn update_environment(
 
     // TODO(charlie): Respect project configuration.
     let build_isolation = BuildIsolation::default();
+    let compile = false;
+    let concurrency = Concurrency::default();
     let config_settings = ConfigSettings::default();
+    let dry_run = false;
+    let extras = ExtrasSpecification::default();
     let flat_index = FlatIndex::default();
     let hasher = HashStrategy::default();
     let in_flight = InFlight::default();
@@ -178,14 +182,11 @@ pub(crate) async fn update_environment(
     let link_mode = LinkMode::default();
     let no_binary = NoBinary::default();
     let no_build = NoBuild::default();
-    let setup_py = SetupPyStrategy::default();
-    let concurrency = Concurrency::default();
-    let reinstall = Reinstall::default();
-    let compile = false;
-    let dry_run = false;
-    let extras = ExtrasSpecification::default();
-    let upgrade = Upgrade::default();
     let options = Options::default();
+    let preferences = Vec::default();
+    let reinstall = Reinstall::default();
+    let setup_py = SetupPyStrategy::default();
+    let upgrade = Upgrade::default();
 
     // Create a build dispatch.
     let resolve_dispatch = BuildDispatch::new(
@@ -213,6 +214,7 @@ pub(crate) async fn update_environment(
         spec.source_trees,
         spec.project,
         &extras,
+        preferences,
         site_packages.clone(),
         &hasher,
         &reinstall,