fix(tools): keep searching past broken Python aliases

Installing debugpy on Windows failed with "cannot run python3.exe … (os error 3)": the tool
manager looked for `python3` first, and on Windows that only finds the App Execution Alias in
WindowsApps, which can't start without the Store's Python. Windows installs `python.exe` and the
`py` launcher instead. On Windows the interpreter is now looked up as `python`, `py`, then
`python3`, and a WindowsApps alias only counts when it runs. The debugpy adapter's default
interpreter is `python` on Windows too. macOS and Linux keep `python3` first.

crates/ide-dap/src/adapter.rs

@@ -72,7 +72,13 @@ fn builtin(adapter: &str) -> Option<DebuggerConfig> {
             "stdio",
             "Install the Kotlin Debug Adapter from Settings > Language Servers",
         ),
-        "debugpy" => cfg("python3", &["-m", "debugpy.adapter"], "stdio", "pip install debugpy"),
+        // Windows installs `python.exe`; `python3.exe` there is at most a Store alias.
+        "debugpy" => cfg(
+            if cfg!(windows) { "python" } else { "python3" },
+            &["-m", "debugpy.adapter"],
+            "stdio",
+            "pip install debugpy",
+        ),
         "js-debug" => cfg(
             "js-debug-adapter",
             // Without a host it listens on `localhost`, which may resolve to ::1 only.

crates/ide-tools/src/lib.rs

@@ -395,6 +395,11 @@ pub fn parse_version(text: &str) -> Option<String> {
     None
 }
 
+/// A Windows App Execution Alias (`%LOCALAPPDATA%\Microsoft\WindowsApps\python.exe`).
+fn is_app_execution_alias(path: &Path) -> bool {
+    path.parent().and_then(Path::file_name).is_some_and(|d| d.eq_ignore_ascii_case("WindowsApps"))
+}
+
 /// A tool whose "command" is a plugin jar (e.g. a jdtls bundle) rather than an executable.
 fn is_bundle(command: &str) -> bool {
     command.ends_with(".jar")
@@ -491,8 +496,32 @@ impl Tools {
         cmd
     }
 
+    /// The interpreter that installs and probes Python tools. Windows installs `python.exe`
+    /// and the `py` launcher, not `python3.exe`; its `WindowsApps` entries are App Execution
+    /// Aliases that only open the Store unless the Store's Python is installed, so they count
+    /// only when they run.
     fn python(&self) -> Option<PathBuf> {
-        self.which_any(&["python3", "python"])
+        if self.platform.os != Os::Windows {
+            return self.which_any(&["python3", "python"]);
+        }
+        ["python", "py", "python3"]
+            .into_iter()
+            .flat_map(|command| {
+                std::env::split_paths(&self.system_path).filter_map(move |dir| {
+                    if dir.as_os_str().is_empty() {
+                        return None;
+                    }
+                    let search = std::env::join_paths([dir]).ok()?;
+                    ide_core::tool_path::find_command(command, &search, &self.root)
+                })
+            })
+            .find(|p| {
+                !is_app_execution_alias(p) || {
+                    let mut c = self.python_command(p);
+                    c.arg("--version");
+                    run_quiet(c, Duration::from_secs(5)).is_some_and(|(ok, _)| ok)
+                }
+            })
     }
 
     /// Executable `cmd` inside `dir`, honouring Windows suffixes.

crates/ide-tools/src/tests.rs

@@ -37,6 +37,12 @@ impl Env {
         fs::write(&p, format!("#!/bin/sh\n{body}\n")).unwrap();
         archive::make_executable(&p).unwrap();
     }
+
+    #[cfg(windows)]
+    fn script(&self, dir: &Path, name: &str, body: &str) {
+        fs::create_dir_all(dir).unwrap();
+        fs::write(dir.join(format!("{name}.cmd")), format!("@echo off\r\n{body}\r\n")).unwrap();
+    }
 }
 
 fn find<'a>(list: &'a [ToolInfo], name: &str) -> &'a ToolInfo {
@@ -700,6 +706,34 @@ fn rust_analyzer_managed_copy_survives_rustup_becoming_available() {
     assert!(!env.root.join("rust-analyzer").exists());
 }
 
+/// Windows has `python.exe` and `py`, not `python3.exe`; the `WindowsApps` aliases only count
+/// when the Store's Python behind them runs.
+#[test]
+fn windows_python_skips_store_aliases_that_do_not_run() {
+    let env = Env::new();
+    let aliases = env.sys.parent().unwrap().join("Microsoft").join("WindowsApps");
+    env.script(&aliases, "python", "exit 9009");
+    env.script(&aliases, "python3", "exit 9009");
+    env.script(&env.sys, "py", "echo Python 3.12.0");
+    let windows = Platform { os: Os::Windows, arch: platform::Arch::X64 };
+    let found = || {
+        let dirs = std::env::join_paths([aliases.clone(), env.sys.clone()]).unwrap();
+        Tools::with_paths(env.root.clone(), dirs, windows).python().map(|python| {
+            let dir = python.parent().unwrap().file_name().unwrap().to_string_lossy().into_owned();
+            format!("{dir}/{}", python.file_stem().unwrap().to_string_lossy())
+        })
+    };
+    assert_eq!(found().as_deref(), Some("sysbin/py"));
+    fs::remove_file(env.sys.join(if cfg!(windows) { "py.cmd" } else { "py" })).unwrap();
+    assert_eq!(found(), None, "only broken aliases are available");
+    env.script(&env.sys, "python3", "echo Python 3.12.0");
+    assert_eq!(found().as_deref(), Some("sysbin/python3"), "python3 is the final fallback");
+    env.script(&env.sys, "python", "echo Python 3.12.0");
+    assert_eq!(found().as_deref(), Some("sysbin/python"), "a broken alias must not hide a later interpreter");
+    env.script(&aliases, "python", "echo Python 3.13.0");
+    assert_eq!(found().as_deref(), Some("WindowsApps/python"), "the Store's Python runs");
+}
+
 #[cfg(unix)]
 #[test]
 fn python_probes_run_in_an_empty_private_directory() {