feat: pythonw support on gui scripts (#4409)

## Summary

Closes https://github.com/astral-sh/uv/issues/2956

This changes the bootstrap launcher script to use `pythonw.exe` instead
of `python.exe` on `gui_scripts` via a helper fn both in the shebang and
the python exe path encoded before `UVUV` magic, that way
uv-trampoline's `find_python_exe` can use the right pythonw executable.

## Test Plan

New unit tests for the helper was added.
Tested on example from #2956 on Windows to make sure it works as
expected.

## Questions

I noticed the docs in `fn windows_script_launcher` says ```The launcher
will look for `python[w].exe` adjacent to it in the same directory to
start the embedded script.``` but I didn't find such functionality when
I looked in uv-trampoline.
I only saw `clear_app_starting_state` getting called when `is_gui` is
set.

Was the intention to do this in uv-trampoline at some point instead?

---------

Co-authored-by: konstin <konstin@mailbox.org>

crates/install-wheel-rs/Cargo.toml

@@ -50,4 +50,6 @@ walkdir = { workspace = true }
 zip = { workspace = true }
 
 [dev-dependencies]
+anyhow = { version = "1.0.80" }
+assert_fs = { version = "1.1.1" }
 indoc = { version = "2.0.4" }

crates/install-wheel-rs/src/wheel.rs

@@ -152,8 +152,7 @@ fn format_shebang(executable: impl AsRef<Path>, os_name: &str) -> String {
 }
 
 /// A Windows script is a minimal .exe launcher binary with the python entrypoint script appended as
-/// stored zip file. The launcher will look for `python[w].exe` adjacent to it in the same directory
-/// to start the embedded script.
+/// stored zip file.
 ///
 /// <https://github.com/pypa/pip/blob/fd0ea6bc5e8cb95e518c23d901c26ca14db17f89/src/pip/_vendor/distlib/scripts.py#L248-L262>
 #[allow(unused_variables)]
@@ -233,6 +232,20 @@ pub(crate) fn windows_script_launcher(
     Ok(launcher)
 }
 
+/// Returns a [`PathBuf`] to `python[w].exe` for script execution.
+fn get_script_executable(python_executable: &Path, is_gui: bool) -> PathBuf {
+    // Only check for pythonw.exe on Windows
+    if cfg!(windows) && is_gui {
+        python_executable
+            .parent()
+            .map(|parent| parent.join("pythonw.exe"))
+            .filter(|path| path.is_file())
+            .unwrap_or_else(|| python_executable.to_path_buf())
+    } else {
+        python_executable.to_path_buf()
+    }
+}
+
 /// Create the wrapper scripts in the bin folder of the venv for launching console scripts.
 pub(crate) fn write_script_entrypoints(
     layout: &Layout,
@@ -269,9 +282,10 @@ pub(crate) fn write_script_entrypoints(
             })?;
 
         // Generate the launcher script.
+        let launcher_executable = get_script_executable(&layout.sys_executable, is_gui);
         let launcher_python_script = get_script_launcher(
             entrypoint,
-            &format_shebang(&layout.sys_executable, &layout.os_name),
+            &format_shebang(&launcher_executable, &layout.os_name),
         );
 
         // If necessary, wrap the launcher script in a Windows launcher binary.
@@ -279,7 +293,7 @@ pub(crate) fn write_script_entrypoints(
             write_file_recorded(
                 site_packages,
                 &entrypoint_relative,
-                &windows_script_launcher(&launcher_python_script, is_gui, &layout.sys_executable)?,
+                &windows_script_launcher(&launcher_python_script, is_gui, &launcher_executable)?,
                 record,
             )?;
         } else {
@@ -722,12 +736,16 @@ mod test {
     use std::io::Cursor;
     use std::path::Path;
 
+    use anyhow::Result;
+    use assert_fs::prelude::*;
     use indoc::{formatdoc, indoc};
 
     use crate::wheel::format_shebang;
     use crate::Error;
 
-    use super::{parse_key_value_file, parse_wheel_file, read_record_file, Script};
+    use super::{
+        get_script_executable, parse_key_value_file, parse_wheel_file, read_record_file, Script,
+    };
 
     #[test]
     fn test_parse_key_value_file() {
@@ -922,4 +940,36 @@ mod test {
             super::LAUNCHER_AArch64_CONSOLE.len()
         );
     }
+
+    #[test]
+    fn test_script_executable() -> Result<()> {
+        // Test with adjacent pythonw.exe
+        let temp_dir = assert_fs::TempDir::new()?;
+        let python_exe = temp_dir.child("python.exe");
+        let pythonw_exe = temp_dir.child("pythonw.exe");
+        python_exe.write_str("")?;
+        pythonw_exe.write_str("")?;
+
+        let script_path = get_script_executable(&python_exe, true);
+        #[cfg(windows)]
+        assert_eq!(script_path, pythonw_exe.to_path_buf());
+        #[cfg(not(windows))]
+        assert_eq!(script_path, python_exe.to_path_buf());
+
+        let script_path = get_script_executable(&python_exe, false);
+        assert_eq!(script_path, python_exe.to_path_buf());
+
+        // Test without adjacent pythonw.exe
+        let temp_dir = assert_fs::TempDir::new()?;
+        let python_exe = temp_dir.child("python.exe");
+        python_exe.write_str("")?;
+
+        let script_path = get_script_executable(&python_exe, true);
+        assert_eq!(script_path, python_exe.to_path_buf());
+
+        let script_path = get_script_executable(&python_exe, false);
+        assert_eq!(script_path, python_exe.to_path_buf());
+
+        Ok(())
+    }
 }