Discover Microsoft Store Pythons (#6807)

Microsoft Store Pythons do not always register themselves in the
registry, so we port
<https://github.com/python/cpython/blob/58ce131037ecb34d506a613f21993cde2056f628/PC/launcher2.c#L1744>
and look them up on the filesystem in known locations.

## Test Plan

So far I've confirmed that we find a store Python when I use `cargo run
python list`, can we make this a part of any of the platform tests
maybe?

crates/uv-python/src/discovery.rs

@@ -21,7 +21,9 @@ use crate::installation::PythonInstallation;
 use crate::interpreter::Error as InterpreterError;
 use crate::managed::ManagedPythonInstallations;
 #[cfg(windows)]
-use crate::py_launcher::registry_pythons;
+use crate::microsoft_store::find_microsoft_store_pythons;
+#[cfg(windows)]
+use crate::py_launcher::{registry_pythons, WindowsPython};
 use crate::virtualenv::{
     conda_prefix_from_env, virtualenv_from_env, virtualenv_from_working_dir,
     virtualenv_python_executable,
@@ -167,6 +169,8 @@ pub enum PythonSource {
     SearchPath,
     /// An executable was found in the Windows registry via PEP 514
     Registry,
+    /// An executable was found in the known Microsoft Store locations
+    MicrosoftStore,
     /// The Python installation was found in the uv managed Python directory
     Managed,
     /// The Python installation was found via the invoking interpreter i.e. via `python -m uv ...`
@@ -308,30 +312,36 @@ fn python_executables_from_installed<'a>(
     })
     .flatten();
 
-    let from_py_launcher = std::iter::once_with(move || {
+    let from_windows = std::iter::once_with(move || {
         #[cfg(windows)]
         {
+            // Skip interpreter probing if we already know the version doesn't match.
+            let version_filter = move |entry: &WindowsPython| {
+                if let Some(version_request) = version {
+                    if let Some(version) = &entry.version {
+                        version_request.matches_version(version)
+                    } else {
+                        true
+                    }
+                } else {
+                    true
+                }
+            };
+
             env::var_os("UV_TEST_PYTHON_PATH")
                 .is_none()
                 .then(|| {
                     registry_pythons()
                         .map(|entries| {
                             entries
                                 .into_iter()
-                                .filter(move |entry| {
-                                    // Skip interpreter probing if we already know the version
-                                    // doesn't match.
-                                    if let Some(version_request) = version {
-                                        if let Some(version) = &entry.version {
-                                            version_request.matches_version(version)
-                                        } else {
-                                            true
-                                        }
-                                    } else {
-                                        true
-                                    }
-                                })
+                                .filter(version_filter)
                                 .map(|entry| (PythonSource::Registry, entry.path))
+                                .chain(
+                                    find_microsoft_store_pythons()
+                                        .filter(version_filter)
+                                        .map(|entry| (PythonSource::MicrosoftStore, entry.path)),
+                                )
                         })
                         .map_err(Error::from)
                 })
@@ -350,14 +360,14 @@ fn python_executables_from_installed<'a>(
         PythonPreference::Managed => Box::new(
             from_managed_installations
                 .chain(from_search_path)
-                .chain(from_py_launcher),
+                .chain(from_windows),
         ),
         PythonPreference::System => Box::new(
             from_search_path
-                .chain(from_py_launcher)
+                .chain(from_windows)
                 .chain(from_managed_installations),
         ),
-        PythonPreference::OnlySystem => Box::new(from_search_path.chain(from_py_launcher)),
+        PythonPreference::OnlySystem => Box::new(from_search_path.chain(from_windows)),
     }
 }
 
@@ -1633,6 +1643,7 @@ impl fmt::Display for PythonSource {
             Self::DiscoveredEnvironment => f.write_str("virtual environment"),
             Self::SearchPath => f.write_str("search path"),
             Self::Registry => f.write_str("registry"),
+            Self::MicrosoftStore => f.write_str("Microsoft Store"),
             Self::Managed => f.write_str("managed installations"),
             Self::ParentInterpreter => f.write_str("parent interpreter"),
         }

crates/uv-python/src/lib.rs

@@ -26,6 +26,8 @@ mod installation;
 mod interpreter;
 mod libc;
 pub mod managed;
+#[cfg(windows)]
+mod microsoft_store;
 pub mod platform;
 mod pointer_size;
 mod prefix;

crates/uv-python/src/microsoft_store.rs

@@ -0,0 +1,118 @@
+//! Microsoft Store Pythons don't register themselves in the registry, so we have to look for them
+//! in known locations.
+//!
+//! Effectively a port of <https://github.com/python/cpython/blob/58ce131037ecb34d506a613f21993cde2056f628/PC/launcher2.c#L1744>
+
+use crate::py_launcher::WindowsPython;
+use crate::PythonVersion;
+use itertools::Either;
+use std::env;
+use std::path::PathBuf;
+use std::str::FromStr;
+use tracing::debug;
+
+#[derive(Debug)]
+struct MicrosoftStorePython {
+    family_name: &'static str,
+    version: &'static str,
+}
+
+/// List of known Microsoft Store Pythons.
+///
+/// Copied from <https://github.com/python/cpython/blob/58ce131037ecb34d506a613f21993cde2056f628/PC/launcher2.c#L1963-L1985>,
+/// please update when upstream changes.
+const MICROSOFT_STORE_PYTHONS: &[MicrosoftStorePython] = &[
+    // Releases made through the Store
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.13_qbz5n2kfra8p0",
+        version: "3.13",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.12_qbz5n2kfra8p0",
+        version: "3.12",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.11_qbz5n2kfra8p0",
+        version: "3.11",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.10_qbz5n2kfra8p0",
+        version: "3.10",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.9_qbz5n2kfra8p0",
+        version: "3.9",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.8_qbz5n2kfra8p0",
+        version: "3.8",
+    },
+    // Side-loadable releases
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.13_3847v3x7pw1km",
+        version: "3.13",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.12_3847v3x7pw1km",
+        version: "3.12",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.11_3847v3x7pw1km",
+        version: "3.11",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.11_hd69rhyc2wevp",
+        version: "3.11",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.10_3847v3x7pw1km",
+        version: "3.10",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.10_hd69rhyc2wevp",
+        version: "3.10",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.9_3847v3x7pw1km",
+        version: "3.9",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.9_hd69rhyc2wevp",
+        version: "3.9",
+    },
+    MicrosoftStorePython {
+        family_name: "PythonSoftwareFoundation.Python.3.8_hd69rhyc2wevp",
+        version: "3.8",
+    },
+];
+
+/// Microsoft Store Pythons don't register themselves in the registry, so we have to look for them
+/// in known locations.
+///
+/// Effectively a port of <https://github.com/python/cpython/blob/58ce131037ecb34d506a613f21993cde2056f628/PC/launcher2.c#L1744>
+pub(crate) fn find_microsoft_store_pythons() -> impl Iterator<Item = WindowsPython> {
+    let Ok(local_app_data) = env::var("LOCALAPPDATA") else {
+        debug!("`LOCALAPPDATA` not set, ignoring Microsoft store Pythons");
+        return Either::Left(std::iter::empty());
+    };
+
+    let windows_apps = PathBuf::from(local_app_data)
+        .join("Microsoft")
+        .join("WindowsApps");
+
+    Either::Right(
+        MICROSOFT_STORE_PYTHONS
+            .iter()
+            .map(move |store_python| {
+                let path = windows_apps
+                    .join(store_python.family_name)
+                    .join("python.exe");
+                WindowsPython {
+                    path,
+                    // All versions are constants, we know they are valid.
+                    version: Some(PythonVersion::from_str(store_python.version).unwrap()),
+                }
+            })
+            .filter(|windows_python| windows_python.path.is_file()),
+    )
+}

crates/uv-python/src/py_launcher.rs

@@ -4,12 +4,13 @@ use std::str::FromStr;
 use tracing::debug;
 use windows_registry::{Key, Value, CURRENT_USER, LOCAL_MACHINE};
 
-/// A Python interpreter found in the Windows registry through PEP 514.
+/// A Python interpreter found in the Windows registry through PEP 514 or from a known Microsoft
+/// Store path.
 ///
 /// There are a lot more (optional) fields defined in PEP 514, but we only care about path and
 /// version here, for everything else we probe with a Python script.
 #[derive(Debug, Clone)]
-pub(crate) struct RegistryPython {
+pub(crate) struct WindowsPython {
     pub(crate) path: PathBuf,
     pub(crate) version: Option<PythonVersion>,
 }
@@ -24,7 +25,7 @@ fn value_to_string(value: Value) -> Option<String> {
 }
 
 /// Find all Pythons registered in the Windows registry following PEP 514.
-pub(crate) fn registry_pythons() -> Result<Vec<RegistryPython>, windows_result::Error> {
+pub(crate) fn registry_pythons() -> Result<Vec<WindowsPython>, windows_result::Error> {
     let mut registry_pythons = Vec::new();
     for root_key in [CURRENT_USER, LOCAL_MACHINE] {
         let Ok(key_python) = root_key.open(r"Software\Python") else {
@@ -67,7 +68,7 @@ pub(crate) fn registry_pythons() -> Result<Vec<RegistryPython>, windows_result::
     Ok(registry_pythons)
 }
 
-fn read_registry_entry(company: &str, tag: &str, tag_key: &Key) -> Option<RegistryPython> {
+fn read_registry_entry(company: &str, tag: &str, tag_key: &Key) -> Option<WindowsPython> {
     // `ExecutablePath` is mandatory for executable Pythons.
     let Some(executable_path) = tag_key
         .open("InstallPath")
@@ -101,7 +102,7 @@ fn read_registry_entry(company: &str, tag: &str, tag_key: &Key) -> Option<Regist
             }
         });
 
-    Some(RegistryPython {
+    Some(WindowsPython {
         path: PathBuf::from(executable_path),
         version,
     })