Check version compatibility for uv python pin without args

crates/uv/src/commands/python/pin.rs

@@ -35,6 +35,25 @@ pub(crate) async fn pin(
         // Display the current pinned Python version
         if let Some(pins) = requests_from_version_file().await? {
             for pin in pins {
+                let python = match PythonInstallation::find(
+                    &pin,
+                    EnvironmentPreference::OnlySystem,
+                    python_preference,
+                    cache,
+                ) {
+                    Ok(python) => Some(python),
+                    // If no matching Python version is found, don't fail unless `resolved` was requested
+                    Err(uv_python::Error::MissingPython(err)) if !resolved => {
+                        warn_user_once!("{}", err);
+                        None
+                    }
+                    Err(err) => return Err(err.into()),
+                };
+                if !isolated {
+                    if let Some(ref python) = python {
+                        assert_python_compatibility(python).await?;
+                    }
+                }
                 writeln!(printer.stdout(), "{}", pin.to_canonical_string())?;
             }
             return Ok(ExitStatus::Success);
@@ -59,35 +78,8 @@ pub(crate) async fn pin(
     };
 
     if !isolated {
-        if let Ok(project) = VirtualProject::discover(&std::env::current_dir()?, None).await {
-            let (requires_python, project_type) = match project {
-                VirtualProject::Project(project_workspace) => {
-                    debug!(
-                        "Discovered project `{}` at: {}",
-                        project_workspace.project_name(),
-                        project_workspace.workspace().install_path().display()
-                    );
-                    let requires_python = find_requires_python(project_workspace.workspace())?;
-                    (requires_python, "project")
-                }
-                VirtualProject::Virtual(workspace) => {
-                    debug!(
-                        "Discovered virtual workspace at: {}",
-                        workspace.install_path().display()
-                    );
-                    let requires_python = find_requires_python(&workspace)?;
-                    (requires_python, "virtual")
-                }
-            };
-            let python_version = python
-                .as_ref()
-                .map(uv_python::PythonInstallation::python_version);
-            if let (Some(requires_python), Some(python_version)) = (requires_python, python_version)
-            {
-                if !requires_python.contains(python_version) {
-                    anyhow::bail!("The pinned Python version is incompatible with the {project_type}'s `Requires-Python` of {requires_python}.");
-                }
-            }
+        if let Some(ref python) = python {
+            assert_python_compatibility(python).await?;
         }
     }
 
@@ -117,3 +109,39 @@ pub(crate) async fn pin(
 
     Ok(ExitStatus::Success)
 }
+
+/// Checks if the pinned Python version is compatible with the workspace/project's `Requires-Python`.
+async fn assert_python_compatibility(python: &uv_python::PythonInstallation) -> Result<()> {
+    if let Ok(project) = VirtualProject::discover(&std::env::current_dir()?, None).await {
+        let (requires_python, project_type) = match project {
+            VirtualProject::Project(project_workspace) => {
+                debug!(
+                    "Discovered project `{}` at: {}",
+                    project_workspace.project_name(),
+                    project_workspace.workspace().install_path().display()
+                );
+                let requires_python = find_requires_python(project_workspace.workspace())?;
+                (requires_python, "project")
+            }
+            VirtualProject::Virtual(workspace) => {
+                debug!(
+                    "Discovered virtual workspace at: {}",
+                    workspace.install_path().display()
+                );
+                let requires_python = find_requires_python(&workspace)?;
+                (requires_python, "virtual")
+            }
+        };
+
+        if let Some(requires_python) = requires_python {
+            if !requires_python.contains(python.python_version()) {
+                anyhow::bail!(
+                    "The pinned Python version is incompatible with the {}'s `Requires-Python` of {}.",
+                    project_type,
+                    requires_python
+                );
+            }
+        }
+    }
+    Ok(())
+}

crates/uv/tests/python_pin.rs

@@ -232,32 +232,32 @@ fn python_pin_no_python() {
 
 #[test]
 fn python_pin_compatible_with_requires_python() -> anyhow::Result<()> {
-    let context: TestContext = TestContext::new_with_versions(&["3.11", "3.12"]);
+    let context: TestContext = TestContext::new_with_versions(&["3.10", "3.11"]);
     let pyproject_toml = context.temp_dir.child("pyproject.toml");
     pyproject_toml.write_str(
         r#"
         [project]
         name = "project"
         version = "0.1.0"
-        requires-python = ">=3.12"
+        requires-python = ">=3.11"
         dependencies = ["iniconfig"]
         "#,
     )?;
 
-    uv_snapshot!(context.filters(), context.python_pin().arg("3.11"), @r###"
+    uv_snapshot!(context.filters(), context.python_pin().arg("3.10"), @r###"
         success: false
         exit_code: 2
         ----- stdout -----
 
         ----- stderr -----
-        error: The pinned Python version is incompatible with the project's `Requires-Python` of >=3.12.
+        error: The pinned Python version is incompatible with the project's `Requires-Python` of >=3.11.
         "###);
 
-    uv_snapshot!(context.filters(), context.python_pin().arg("3.12"), @r###"
+    uv_snapshot!(context.filters(), context.python_pin().arg("3.11"), @r###"
         success: true
         exit_code: 0
         ----- stdout -----
-        Pinned to `3.12`
+        Pinned to `3.11`
 
         ----- stderr -----
         "###);
@@ -268,9 +268,48 @@ fn python_pin_compatible_with_requires_python() -> anyhow::Result<()> {
         filters => context.filters(),
     }, {
         assert_snapshot!(python_version, @r###"
-        3.12
+        3.11
         "###);
     });
+
+    // Updating `requires-python` should affect `uv python pin` compatibilities.
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["iniconfig"]
+        "#,
+    )?;
+
+    uv_snapshot!(context.filters(), context.python_pin(), @r###"
+        success: false
+        exit_code: 2
+        ----- stdout -----
+
+        ----- stderr -----
+        error: The pinned Python version is incompatible with the project's `Requires-Python` of >=3.12.
+        "###);
+
+    Ok(())
+}
+
+#[test]
+fn warning_pinned_python_version_not_installed() -> anyhow::Result<()> {
+    let context: TestContext = TestContext::new_with_versions(&["3.10", "3.11"]);
+    let python_version_file = context.temp_dir.child(PYTHON_VERSION_FILENAME);
+    python_version_file.write_str(r"3.12")?;
+    uv_snapshot!(context.filters(), context.python_pin(), @r###"
+        success: true
+        exit_code: 0
+        ----- stdout -----
+        3.12
+
+        ----- stderr -----
+        warning: No interpreter found for Python 3.12 in system path
+        "###);
+
     Ok(())
 }