Change Operations API to always accept PythonRequirement (#4498)

## Summary

I think this is more intuitive than taking an `Option` and computing the
requirement if it's `None`.

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

@@ -211,9 +211,11 @@ pub(crate) async fn pip_compile(
     };
 
     // Determine the Python requirement, if the user requested a specific version.
-    let python_requirement = python_version
-        .as_ref()
-        .map(|python_version| PythonRequirement::from_python_version(&interpreter, python_version));
+    let python_requirement = if let Some(python_version) = python_version.as_ref() {
+        PythonRequirement::from_python_version(&interpreter, python_version)
+    } else {
+        PythonRequirement::from_interpreter(&interpreter)
+    };
 
     // Determine the environment for the resolution.
     let (tags, markers) = resolution_environment(python_version, python_platform, &interpreter)?;
@@ -316,7 +318,6 @@ pub(crate) async fn pip_compile(
         &hasher,
         &Reinstall::None,
         &upgrade,
-        &interpreter,
         Some(&tags),
         Some(&markers),
         python_requirement,

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

@@ -23,7 +23,7 @@ use uv_installer::{SatisfiesResult, SitePackages};
 use uv_requirements::{RequirementsSource, RequirementsSpecification};
 use uv_resolver::{
     DependencyMode, ExcludeNewer, FlatIndex, InMemoryIndex, OptionsBuilder, PreReleaseMode,
-    ResolutionMode,
+    PythonRequirement, ResolutionMode,
 };
 use uv_toolchain::{
     EnvironmentPreference, Prefix, PythonEnvironment, PythonVersion, Target, ToolchainRequest,
@@ -218,6 +218,13 @@ pub(crate) async fn pip_install(
 
     let interpreter = environment.interpreter();
 
+    // Determine the Python requirement, if the user requested a specific version.
+    let python_requirement = if let Some(python_version) = python_version.as_ref() {
+        PythonRequirement::from_python_version(interpreter, python_version)
+    } else {
+        PythonRequirement::from_interpreter(interpreter)
+    };
+
     // Determine the environment for the resolution.
     let (tags, markers) = resolution_environment(python_version, python_platform, interpreter)?;
 
@@ -327,10 +334,9 @@ pub(crate) async fn pip_install(
         &hasher,
         &reinstall,
         &upgrade,
-        interpreter,
         Some(&tags),
         Some(&markers),
-        None,
+        python_requirement,
         &client,
         &flat_index,
         &index,

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

@@ -37,7 +37,7 @@ use uv_resolver::{
     DependencyMode, Exclusions, FlatIndex, InMemoryIndex, Manifest, Options, Preference,
     Preferences, PythonRequirement, ResolutionGraph, Resolver,
 };
-use uv_toolchain::{Interpreter, PythonEnvironment};
+use uv_toolchain::PythonEnvironment;
 use uv_types::{HashStrategy, InFlight, InstalledPackagesProvider};
 use uv_warnings::warn_user;
 
@@ -87,10 +87,9 @@ pub(crate) async fn resolve<InstalledPackages: InstalledPackagesProvider>(
     hasher: &HashStrategy,
     reinstall: &Reinstall,
     upgrade: &Upgrade,
-    interpreter: &Interpreter,
     tags: Option<&Tags>,
     markers: Option<&MarkerEnvironment>,
-    python_requirement: Option<PythonRequirement>,
+    python_requirement: PythonRequirement,
     client: &RegistryClient,
     flat_index: &FlatIndex,
     index: &InMemoryIndex,
@@ -186,10 +185,6 @@ pub(crate) async fn resolve<InstalledPackages: InstalledPackagesProvider>(
     let overrides = Overrides::from_requirements(overrides);
     let preferences = Preferences::from_iter(preferences, markers);
 
-    // Determine the Python requirement, defaulting to that of the interpreter.
-    let python_requirement =
-        python_requirement.unwrap_or_else(|| PythonRequirement::from_interpreter(interpreter));
-
     // Determine any lookahead requirements.
     let lookaheads = match options.dependency_mode {
         DependencyMode::Transitive => {

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

@@ -22,7 +22,7 @@ use uv_installer::SitePackages;
 use uv_requirements::{RequirementsSource, RequirementsSpecification};
 use uv_resolver::{
     DependencyMode, ExcludeNewer, FlatIndex, InMemoryIndex, OptionsBuilder, PreReleaseMode,
-    ResolutionMode,
+    PythonRequirement, ResolutionMode,
 };
 use uv_toolchain::{
     EnvironmentPreference, Prefix, PythonEnvironment, PythonVersion, Target, ToolchainRequest,
@@ -169,6 +169,13 @@ pub(crate) async fn pip_sync(
 
     let interpreter = environment.interpreter();
 
+    // Determine the Python requirement, if the user requested a specific version.
+    let python_requirement = if let Some(python_version) = python_version.as_ref() {
+        PythonRequirement::from_python_version(interpreter, python_version)
+    } else {
+        PythonRequirement::from_interpreter(interpreter)
+    };
+
     // Determine the environment for the resolution.
     let (tags, markers) = resolution_environment(python_version, python_platform, interpreter)?;
 
@@ -279,10 +286,9 @@ pub(crate) async fn pip_sync(
         &hasher,
         &reinstall,
         &upgrade,
-        interpreter,
         Some(&tags),
         Some(&markers),
-        None,
+        python_requirement,
         &client,
         &flat_index,
         &index,

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

@@ -220,10 +220,9 @@ pub(super) async fn do_lock(
         &hasher,
         &Reinstall::default(),
         upgrade,
-        interpreter,
         None,
         None,
-        Some(python_requirement),
+        python_requirement,
         &client,
         &flat_index,
         &index,

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

@@ -16,7 +16,7 @@ use uv_fs::Simplified;
 use uv_git::GitResolver;
 use uv_installer::{SatisfiesResult, SitePackages};
 use uv_requirements::{RequirementsSource, RequirementsSpecification};
-use uv_resolver::{FlatIndex, InMemoryIndex, OptionsBuilder, RequiresPython};
+use uv_resolver::{FlatIndex, InMemoryIndex, OptionsBuilder, PythonRequirement, RequiresPython};
 use uv_toolchain::{
     request_from_version_file, EnvironmentPreference, Interpreter, PythonEnvironment, Toolchain,
     ToolchainPreference, ToolchainRequest, VersionRequest,
@@ -345,6 +345,7 @@ pub(crate) async fn update_environment(
     let interpreter = venv.interpreter();
     let tags = venv.interpreter().tags()?;
     let markers = venv.interpreter().markers();
+    let python_requirement = PythonRequirement::from_interpreter(interpreter);
 
     // Initialize the registry client.
     let client = RegistryClientBuilder::new(cache.clone())
@@ -421,10 +422,9 @@ pub(crate) async fn update_environment(
         &hasher,
         reinstall,
         upgrade,
-        interpreter,
         Some(tags),
         Some(markers),
-        None,
+        python_requirement,
         &client,
         &flat_index,
         &index,