Fix handling of `python install --default` for pre-release Python versions (#16706)

## Summary

Fixes `--default` not creating default executable links for pre-release
Python versions.

When using `--default` with a pre-release version like `3.15.0a1`, the
code was checking `matches_installation()` against the download request
instead of the original user request. This caused the check to fail
since the download request doesn't match pre-release versions the same
way.

Changed it to use `installation.satisfies(&first_request.request)` when
`--default` is used, which checks against the original user request.

Fixes #16696

## Test Plan

Added `python_install_default_prerelease` test that installs Python 3.15
with `--default` and verifies all three executable links (`python3.15`,
`python3`, `python`) are created. The test skips gracefully if 3.15
isn't available.

All existing tests pass.

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

@@ -264,7 +264,7 @@ pub(crate) async fn install(
             .collect::<Result<Vec<_>>>()?
     };
 
-    let Some(first_request) = requests.first() else {
+    if requests.is_empty() {
         if upgrade {
             writeln!(
                 printer.stderr(),
@@ -272,7 +272,7 @@ pub(crate) async fn install(
             )?;
         }
         return Ok(ExitStatus::Success);
-    };
+    }
 
     let requested_minor_versions = requests
         .iter()
@@ -500,7 +500,6 @@ pub(crate) async fn install(
                 upgradeable,
                 upgrade,
                 is_default_install,
-                first_request,
                 &existing_installations,
                 &installations,
                 &mut changelog,
@@ -764,7 +763,6 @@ fn create_bin_links(
     upgradeable: bool,
     upgrade: bool,
     is_default_install: bool,
-    first_request: &InstallRequest,
     existing_installations: &[ManagedPythonInstallation],
     installations: &[&ManagedPythonInstallation],
     changelog: &mut Changelog,
@@ -774,10 +772,10 @@ fn create_bin_links(
     // TODO(zanieb): We want more feedback on the `is_default_install` behavior before stabilizing
     // it. In particular, it may be confusing because it does not apply when versions are loaded
     // from a `.python-version` file.
-    let targets = if (default
-        || (is_default_install && preview.is_enabled(PreviewFeatures::PYTHON_INSTALL_DEFAULT)))
-        && first_request.matches_installation(installation)
-    {
+    let should_create_default_links = default
+        || (is_default_install && preview.is_enabled(PreviewFeatures::PYTHON_INSTALL_DEFAULT));
+
+    let targets = if should_create_default_links {
         vec![
             installation.key().executable_name_minor(),
             installation.key().executable_name_major(),

crates/uv/tests/it/python_install.rs

@@ -2255,6 +2255,45 @@ fn python_install_broken_link() {
     });
 }
 
+/// Test that --default works with pre-release versions (e.g., 3.15.0a1).
+/// This test verifies the fix for issue #16696 where --default didn't create
+/// python.exe and python3.exe links for pre-release versions.
+#[test]
+fn python_install_default_prerelease() {
+    let context: TestContext = TestContext::new_with_versions(&[])
+        .with_filtered_python_keys()
+        .with_filtered_exe_suffix()
+        .with_managed_python_dirs()
+        .with_python_download_cache();
+
+    // Install Python 3.15, which currently only exists as a pre-release (3.15.0a1).
+    context
+        .python_install()
+        .arg("--default")
+        .arg("--preview-features")
+        .arg("python-install-default")
+        .arg("3.15")
+        .assert()
+        .success();
+
+    let bin_python_minor_15 = context
+        .bin_dir
+        .child(format!("python3.15{}", std::env::consts::EXE_SUFFIX));
+
+    let bin_python_major = context
+        .bin_dir
+        .child(format!("python3{}", std::env::consts::EXE_SUFFIX));
+
+    let bin_python_default = context
+        .bin_dir
+        .child(format!("python{}", std::env::consts::EXE_SUFFIX));
+
+    // Verify that all three executables are created when --default is used with a pre-release version
+    bin_python_minor_15.assert(predicate::path::exists());
+    bin_python_major.assert(predicate::path::exists());
+    bin_python_default.assert(predicate::path::exists());
+}
+
 #[test]
 fn python_install_default_from_env() {
     let context: TestContext = TestContext::new_with_versions(&[])