Add Windows x86-32 emulation support to interpreter architecture checks (#13475)

Closes https://github.com/astral-sh/uv/issues/13471

Refactors the logic there a bit too.

---------

Co-authored-by: Aria Desires <aria.desires@gmail.com>

crates/uv-platform/src/lib.rs

@@ -3,6 +3,7 @@
 use std::cmp;
 use std::fmt;
 use std::str::FromStr;
+use target_lexicon::Architecture;
 use thiserror::Error;
 use tracing::trace;
 
@@ -91,13 +92,28 @@ impl Platform {
             return true;
         }
 
-        // Windows ARM64 runs emulated x86_64 binaries transparently
-        // 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 (self.os.is_windows() || self.os.is_macos())
-            && matches!(self.arch.family(), target_lexicon::Architecture::Aarch64(_))
-            && matches!(other.arch.family(), target_lexicon::Architecture::X86_64)
+        #[allow(clippy::unnested_or_patterns)]
+        if self.os.is_windows()
+            && matches!(
+                (self.arch.family(), other.arch.family()),
+                // 32-bit x86 binaries work fine on 64-bit x86 windows
+                (Architecture::X86_64, Architecture::X86_32(_)) |
+                // Both 32-bit and 64-bit binaries are transparently emulated on aarch64 windows
+                (Architecture::Aarch64(_), Architecture::X86_64) |
+                (Architecture::Aarch64(_), Architecture::X86_32(_))
+            )
+        {
+            return true;
+        }
+
+        if self.os.is_macos()
+            && matches!(
+                (self.arch.family(), other.arch.family()),
+                // 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.
+                (Architecture::Aarch64(_), Architecture::X86_64)
+            )
         {
             return true;
         }

crates/uv/tests/it/python_install.rs

@@ -2765,6 +2765,77 @@ fn python_install_emulated_macos() {
     ");
 }
 
+#[cfg(all(target_os = "windows", target_arch = "x86_64"))]
+#[test]
+fn python_install_emulated_windows_x86_on_x64() {
+    let context: TestContext = TestContext::new_with_versions(&[])
+        .with_filtered_exe_suffix()
+        .with_managed_python_dirs()
+        .with_python_download_cache();
+
+    // Before installation, `uv python list` should not show the x86_32 download
+    uv_snapshot!(context.filters(), context.python_list().arg("3.13"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    cpython-3.13.9-windows-x86_64-none    <download available>
+
+    ----- stderr -----
+    ");
+
+    // Install an x86_32 version (assuming an x64 host)
+    uv_snapshot!(context.filters(), context.python_install().arg("3.13-x86"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Installed Python 3.13.9 in [TIME]
+     + cpython-3.13.9-windows-x86-none (python3.13)
+    ");
+
+    // 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-3.13.9-windows-x86-none/python
+
+    ----- 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-3.13.9-windows-x86_64-none    <download available>
+    cpython-3.13.9-windows-x86-none       managed/cpython-3.13.9-windows-x86-none/python
+
+    ----- stderr -----
+    ");
+
+    uv_snapshot!(context.filters(), context.python_install().arg("3.13-x86_64"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Installed Python 3.13.9 in [TIME]
+     + cpython-3.13.9-windows-x86_64-none
+    ");
+
+    // Once we've installed the native version, it should be preferred over x86_32
+    uv_snapshot!(context.filters(), context.python_find().arg("3.13"), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+    [TEMP_DIR]/managed/cpython-3.13.9-windows-x86_64-none/python
+
+    ----- stderr -----
+    ");
+}
+
 // A virtual environment should track the latest patch version installed.
 #[test]
 fn install_transparent_patch_upgrade_uv_venv() {