Prefer stable releases over pre-releases in uv python install (#12194)

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

Closes #12184

crates/uv-python/src/discovery.rs

@@ -2294,9 +2294,9 @@ 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

@@ -485,13 +485,28 @@ 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

@@ -205,10 +205,10 @@ impl TestContext {
             self.filters
                 .push(("python.exe".to_string(), "python".to_string()));
         } else {
-            self.filters
-                .push((r"python\d".to_string(), "python".to_string()));
             self.filters
                 .push((r"python\d.\d\d".to_string(), "python".to_string()));
+            self.filters
+                .push((r"python\d".to_string(), "python".to_string()));
         }
         self
     }
@@ -224,6 +224,25 @@ impl TestContext {
         self
     }
 
+    /// Add extra standard filtering for Python installation `bin/` directories, which are not
+    /// present on Windows but are on Unix. See [`TestContext::with_filtered_virtualenv_bin`] for
+    /// the virtual environment equivalent.
+    #[must_use]
+    pub fn with_filtered_python_install_bin(mut self) -> Self {
+        if cfg!(unix) {
+            self.filters.push((
+                r"[\\/]bin/python".to_string(),
+                "/[INSTALL-BIN]/python".to_string(),
+            ));
+        } else {
+            self.filters.push((
+                r"[\\/]python".to_string(),
+                "/[INSTALL-BIN]/python".to_string(),
+            ));
+        }
+        self
+    }
+
     /// Add extra filtering for ` -> <PATH>` symlink display for Python versions in the test
     /// context, e.g., for use in `uv python list`.
     #[must_use]

crates/uv/tests/it/python_install.rs

@@ -1201,3 +1201,76 @@ 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()
+        .with_filtered_python_names()
+        .with_filtered_python_install_bin();
+
+    // 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 3.14.0a6 in [TIME]
+     + cpython-3.14.0a6-[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]
+    ");
+
+    // We should be able to find this version without opt-in, because there is no stable release
+    // installed
+    uv_snapshot!(context.filters(), context.python_find().arg("3.14"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [TEMP_DIR]/managed/cpython-3.14.0a6-[PLATFORM]/[INSTALL-BIN]/python
+
+    ----- stderr -----
+    ");
+
+    uv_snapshot!(context.filters(), context.python_find().arg("3"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [TEMP_DIR]/managed/cpython-3.14.0a6-[PLATFORM]/[INSTALL-BIN]/python
+
+    ----- stderr -----
+    ");
+
+    // If we install a stable version, that should be preferred though
+    uv_snapshot!(context.filters(), context.python_install().arg("3.13"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Installed Python 3.13.3 in [TIME]
+     + cpython-3.13.3-[PLATFORM]
+    ");
+
+    uv_snapshot!(context.filters(), context.python_find().arg("3"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [TEMP_DIR]/managed/cpython-3.13.3-[PLATFORM]/[INSTALL-BIN]/python
+
+    ----- stderr -----
+    ");
+}