Allow discovery of x86-64 managed Python builds on macOS (#13722)

Replacement for https://github.com/astral-sh/uv/pull/13474 (clobbered by
a changed base)

Once these are explicitly installed, they should be discoverable and
usable. Currently, they are not.

crates/uv-python/src/platform.rs

@@ -143,7 +143,12 @@ impl Arch {
         // TODO: Implement `variant` support checks
 
         // Windows ARM64 runs emulated x86_64 binaries transparently
-        if cfg!(windows) && matches!(self.family, target_lexicon::Architecture::Aarch64(_)) {
+        // Similarly, macOS aarch64 runs emulated x86_64 binaries transparently if you have Rosetta
+        // installed. We don't try to be clever and check if that's the case here, we just assume
+        // that if x86_64 distributions are available, they're usable.
+        if (cfg!(windows) || cfg!(target_os = "macos"))
+            && matches!(self.family, target_lexicon::Architecture::Aarch64(_))
+        {
             return other.family == target_lexicon::Architecture::X86_64;
         }
 

crates/uv/tests/it/python_install.rs

@@ -1416,3 +1416,73 @@ fn python_install_cached() {
       Caused by: An offline Python installation was requested, but cpython-3.12.10[DATE]-[PLATFORM].tar.gz) is missing in python-cache
     ");
 }
+
+#[cfg(target_os = "macos")]
+#[test]
+fn python_install_emulated_macos() {
+    let context: TestContext = TestContext::new_with_versions(&[])
+        .with_filtered_exe_suffix()
+        .with_managed_python_dirs();
+
+    // Before installation, `uv python list` should not show the x86_64 download
+    uv_snapshot!(context.filters(), context.python_list().arg("3.13"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    cpython-3.13.3-macos-aarch64-none    <download available>
+
+    ----- stderr -----
+    ");
+
+    // Install an x86_64 version (assuming an aarch64 host)
+    uv_snapshot!(context.filters(), context.python_install().arg("cpython-3.13-macos-x86_64"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Installed Python 3.13.3 in [TIME]
+     + cpython-3.13.3-macos-x86_64-none
+    ");
+
+    // It should be discoverable with `uv python find`
+    uv_snapshot!(context.filters(), context.python_find().arg("3.13"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [TEMP_DIR]/managed/cpython-3.13.3-macos-x86_64-none/bin/python3.13
+
+    ----- stderr -----
+    ");
+
+    // And included in `uv python list`
+    uv_snapshot!(context.filters(), context.python_list().arg("3.13"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    cpython-3.13.3-macos-aarch64-none    <download available>
+    cpython-3.13.3-macos-x86_64-none     managed/cpython-3.13.3-macos-x86_64-none/bin/python3.13
+
+    ----- stderr -----
+    ");
+
+    uv_snapshot!(context.filters(), context.python_install().arg("cpython-3.13-macos-aarch64"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Installed Python 3.13.3 in [TIME]
+     + cpython-3.13.3-macos-aarch64-none
+    ");
+
+    // Once we've installed the native version, it should be preferred over x86_64
+    uv_snapshot!(context.filters(), context.python_find().arg("3.13"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [TEMP_DIR]/managed/cpython-3.13.3-macos-aarch64-none/bin/python3.13
+
+    ----- stderr -----
+    ");
+}