Prefer stable releases over pre-releases in uv python install

e.g., `uv python install 3` should not install the 3.14 alpha

Author: zanieb

crates/uv-python/src/discovery.rs

@@ -2275,9 +2275,9 @@ impl VersionRequest {
         match self {
             Self::Default => false,
             Self::Any => true,
-            Self::Major(..) => true,
-            Self::MajorMinor(..) => true,
-            Self::MajorMinorPatch(..) => true,
+            Self::Major(..) => false,
+            Self::MajorMinor(..) => false,
+            Self::MajorMinorPatch(..) => false,
             Self::MajorMinorPrerelease(..) => true,
             Self::Range(specifiers, _) => specifiers.iter().any(VersionSpecifier::any_prerelease),
         }

crates/uv-python/src/downloads.rs

@@ -455,13 +455,28 @@ pub enum DownloadResult {
 
 impl ManagedPythonDownload {
     /// Return the first [`ManagedPythonDownload`] matching a request, if any.
+    ///
+    /// If there is no stable version matching the request, a compatible pre-release version will
+    /// be searched for — even if a pre-release was not explicitly requested.
     pub fn from_request(
         request: &PythonDownloadRequest,
     ) -> Result<&'static ManagedPythonDownload, Error> {
-        request
-            .iter_downloads()
-            .next()
-            .ok_or(Error::NoDownloadFound(request.clone()))
+        if let Some(download) = request.iter_downloads().next() {
+            return Ok(download);
+        }
+
+        if !request.allows_prereleases() {
+            if let Some(download) = request
+                .clone()
+                .with_prereleases(true)
+                .iter_downloads()
+                .next()
+            {
+                return Ok(download);
+            }
+        }
+
+        Err(Error::NoDownloadFound(request.clone()))
     }
 
     /// Iterate over all [`ManagedPythonDownload`]s.

crates/uv/tests/it/common/mod.rs

@@ -256,7 +256,7 @@ impl TestContext {
     pub fn with_filtered_python_keys(mut self) -> Self {
         // Filter platform keys
         self.filters.push((
-            r"((?:cpython|pypy)-\d+\.\d+(?:\.(?:\[X\]|\d+))?[a-z]?(?:\+[a-z]+)?)-[a-z0-9]+-[a-z0-9_]+-[a-z]+"
+            r"((?:cpython|pypy)-\d+\.\d+(?:\.(?:\[X\]|\d+(?:[a-z][0-9])?)?[a-z]?(?:\+[a-z]+)?))-[a-z0-9]+-[a-z0-9_]+-[a-z]+"
                 .to_string(),
             "$1-[PLATFORM]".to_string(),
         ));

crates/uv/tests/it/python_install.rs

@@ -1201,3 +1201,34 @@ fn python_install_patch_dylib() {
     ----- stderr -----
     "###);
 }
+
+#[test]
+fn python_install_314() {
+    let context: TestContext = TestContext::new_with_versions(&[])
+        .with_filtered_python_keys()
+        .with_filtered_exe_suffix()
+        .with_managed_python_dirs();
+
+    // Install 3.14
+    // For now, this provides test coverage of pre-release handling
+    uv_snapshot!(context.filters(), context.python_install().arg("3.14"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Installed Python 3.14.0a5 in [TIME]
+     + cpython-3.14.0a5-[PLATFORM]
+    ");
+
+    // Install a specific pre-release
+    uv_snapshot!(context.filters(), context.python_install().arg("3.14.0a4"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Installed Python 3.14.0a4 in [TIME]
+     + cpython-3.14.0a4-[PLATFORM]
+    ");
+}