Check for matching Python implementation during uv python upgrade (#16420)

Closes https://github.com/astral-sh/uv/issues/16416

crates/uv-pep440/src/version.rs

@@ -615,6 +615,13 @@ impl Version {
         Self::new(self.release().iter().copied())
     }
 
+    /// Return the version with any segments apart from the minor version of the release removed.
+    #[inline]
+    #[must_use]
+    pub fn only_minor_release(&self) -> Self {
+        Self::new(self.release().iter().take(2).copied())
+    }
+
     /// Return the version with any segments apart from the release removed, with trailing zeroes
     /// trimmed.
     #[inline]

crates/uv-pep440/src/version_specifier.rs

@@ -394,6 +394,15 @@ impl VersionSpecifier {
         }
     }
 
+    /// Remove all parts of the version beyond the minor segment of the release.
+    #[must_use]
+    pub fn only_minor_release(&self) -> Self {
+        Self {
+            operator: self.operator,
+            version: self.version.only_minor_release(),
+        }
+    }
+
     /// `==<version>`
     pub fn equals_version(version: Version) -> Self {
         Self {

crates/uv-python/src/discovery.rs

@@ -37,7 +37,7 @@ use crate::virtualenv::{
 };
 #[cfg(windows)]
 use crate::windows_registry::{WindowsPython, registry_pythons};
-use crate::{BrokenSymlink, Interpreter, PythonInstallationKey, PythonVersion};
+use crate::{BrokenSymlink, Interpreter, PythonVersion};
 
 /// A request to find a Python installation.
 ///
@@ -2457,9 +2457,26 @@ impl fmt::Display for ExecutableName {
 }
 
 impl VersionRequest {
-    /// Derive a [`VersionRequest::MajorMinor`] from a [`PythonInstallationKey`]
-    pub fn major_minor_request_from_key(key: &PythonInstallationKey) -> Self {
-        Self::MajorMinor(key.major, key.minor, key.variant)
+    /// Drop any patch or prerelease information from the version request.
+    #[must_use]
+    pub fn only_minor(self) -> Self {
+        match self {
+            Self::Any => self,
+            Self::Default => self,
+            Self::Range(specifiers, variant) => Self::Range(
+                specifiers
+                    .into_iter()
+                    .map(|s| s.only_minor_release())
+                    .collect(),
+                variant,
+            ),
+            Self::Major(..) => self,
+            Self::MajorMinor(..) => self,
+            Self::MajorMinorPatch(major, minor, _, variant)
+            | Self::MajorMinorPrerelease(major, minor, _, variant) => {
+                Self::MajorMinor(major, minor, variant)
+            }
+        }
     }
 
     /// Return possible executable names for the given version request.

crates/uv-python/src/downloads.rs

@@ -411,6 +411,10 @@ impl PythonDownloadRequest {
         self.libc.as_ref()
     }
 
+    pub fn take_version(&mut self) -> Option<VersionRequest> {
+        self.version.take()
+    }
+
     /// Iterate over all [`PythonDownload`]'s that match this request.
     pub fn iter_downloads<'a>(
         &'a self,

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

@@ -210,15 +210,19 @@ pub(crate) async fn install(
     let requests: Vec<_> = if targets.is_empty() {
         if upgrade {
             is_unspecified_upgrade = true;
+            // On upgrade, derive requests for all of the existing installations
             let mut minor_version_requests = IndexSet::<InstallRequest>::default();
             for installation in &existing_installations {
-                let request = VersionRequest::major_minor_request_from_key(installation.key());
-                if let Ok(request) = InstallRequest::new(
-                    PythonRequest::Version(request),
+                let mut request = PythonDownloadRequest::from(installation);
+                // We should always have a version in the request from an existing installation
+                let version = request.take_version().unwrap();
+                // Drop the patch and prerelease parts from the request
+                request = request.with_version(version.only_minor());
+                let install_request = InstallRequest::new(
+                    PythonRequest::Key(request),
                     python_downloads_json_url.as_deref(),
-                ) {
-                    minor_version_requests.insert(request);
-                }
+                )?;
+                minor_version_requests.insert(install_request);
             }
             minor_version_requests.into_iter().collect::<Vec<_>>()
         } else {
@@ -284,13 +288,14 @@ pub(crate) async fn install(
         .collect::<IndexSet<_>>();
 
     if upgrade
-        && requests.iter().any(|request| {
+        && let Some(request) = requests.iter().find(|request| {
             request.request.includes_patch() || request.request.includes_prerelease()
         })
     {
         writeln!(
             printer.stderr(),
-            "error: `uv python upgrade` only accepts minor versions"
+            "error: `uv python upgrade` only accepts minor versions, got: {}",
+            request.request.to_canonical_string()
         )?;
         return Ok(ExitStatus::Failure);
     }

crates/uv/tests/it/python_install.rs

@@ -1230,7 +1230,7 @@ fn python_upgrade_not_allowed() {
     ----- stdout -----
 
     ----- stderr -----
-    error: `uv python upgrade` only accepts minor versions
+    error: `uv python upgrade` only accepts minor versions, got: 3.13.0
     ");
 
     // Request a pre-release upgrade
@@ -1240,7 +1240,7 @@ fn python_upgrade_not_allowed() {
     ----- stdout -----
 
     ----- stderr -----
-    error: `uv python upgrade` only accepts minor versions
+    error: `uv python upgrade` only accepts minor versions, got: 3.14rc3
     ");
 }
 

crates/uv/tests/it/python_upgrade.rs

@@ -1,5 +1,6 @@
 use crate::common::{TestContext, uv_snapshot};
 use anyhow::Result;
+use assert_cmd::assert::OutputAssertExt;
 use assert_fs::fixture::FileTouch;
 use assert_fs::prelude::PathChild;
 
@@ -30,7 +31,7 @@ fn python_upgrade() {
     ----- stdout -----
 
     ----- stderr -----
-    error: `uv python upgrade` only accepts minor versions
+    error: `uv python upgrade` only accepts minor versions, got: 3.10.17
     ");
 
     // Upgrade patch version
@@ -737,3 +738,27 @@ fn python_upgrade_force_install() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn python_upgrade_implementation() {
+    let context = TestContext::new_with_versions(&[])
+        .with_python_download_cache()
+        .with_filtered_python_keys()
+        .with_filtered_exe_suffix()
+        .with_empty_python_install_mirror()
+        .with_managed_python_dirs();
+
+    // Install pypy
+    context.python_install().arg("pypy@3.11").assert().success();
+
+    // Run the upgrade, we should not install cpython
+    uv_snapshot!(context.filters(), context.python_upgrade(), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    warning: `uv python upgrade` is experimental and may change without warning. Pass `--preview-features python-upgrade` to disable this warning
+    All versions already on latest supported patch release
+    ");
+}