Suggest unsaved buffer content text as the default filename (#35707)

Closes #24672

This PR complements a feature added earlier by @JosephTLyons (in
https://github.com/zed-industries/zed/pull/32353) where the text is
considered as the tab title in a new buffer. It piggybacks off that
change and sets the title as the suggested filename in the save dialog
(completely mirroring the same functionality in VSCode):

![2025-08-05 11 50
28](https://github.com/user-attachments/assets/49ad9e4a-5559-44b0-a4b0-ae19890e478e)

Release Notes:

- Text entered in a new untitled buffer is considered as the default
filename when saving

crates/gpui/src/platform/linux/platform.rs

@@ -327,26 +327,35 @@ impl<P: LinuxClient + 'static> Platform for P {
         done_rx
     }
 
-    fn prompt_for_new_path(&self, directory: &Path) -> oneshot::Receiver<Result<Option<PathBuf>>> {
+    fn prompt_for_new_path(
+        &self,
+        directory: &Path,
+        suggested_name: Option<&str>,
+    ) -> oneshot::Receiver<Result<Option<PathBuf>>> {
         let (done_tx, done_rx) = oneshot::channel();
 
         #[cfg(not(any(feature = "wayland", feature = "x11")))]
-        let _ = (done_tx.send(Ok(None)), directory);
+        let _ = (done_tx.send(Ok(None)), directory, suggested_name);
 
         #[cfg(any(feature = "wayland", feature = "x11"))]
         self.foreground_executor()
             .spawn({
                 let directory = directory.to_owned();
+                let suggested_name = suggested_name.map(|s| s.to_owned());
 
                 async move {
-                    let request = match ashpd::desktop::file_chooser::SaveFileRequest::default()
-                        .modal(true)
-                        .title("Save File")
-                        .current_folder(directory)
-                        .expect("pathbuf should not be nul terminated")
-                        .send()
-                        .await
-                    {
+                    let mut request_builder =
+                        ashpd::desktop::file_chooser::SaveFileRequest::default()
+                            .modal(true)
+                            .title("Save File")
+                            .current_folder(directory)
+                            .expect("pathbuf should not be nul terminated");
+
+                    if let Some(suggested_name) = suggested_name {
+                        request_builder = request_builder.current_name(suggested_name.as_str());
+                    }
+
+                    let request = match request_builder.send().await {
                         Ok(request) => request,
                         Err(err) => {
                             let result = match err {

crates/gpui/src/platform/mac/platform.rs

@@ -737,8 +737,13 @@ impl Platform for MacPlatform {
         done_rx
     }
 
-    fn prompt_for_new_path(&self, directory: &Path) -> oneshot::Receiver<Result<Option<PathBuf>>> {
+    fn prompt_for_new_path(
+        &self,
+        directory: &Path,
+        suggested_name: Option<&str>,
+    ) -> oneshot::Receiver<Result<Option<PathBuf>>> {
         let directory = directory.to_owned();
+        let suggested_name = suggested_name.map(|s| s.to_owned());
         let (done_tx, done_rx) = oneshot::channel();
         self.foreground_executor()
             .spawn(async move {
@@ -748,6 +753,11 @@ impl Platform for MacPlatform {
                     let url = NSURL::fileURLWithPath_isDirectory_(nil, path, true.to_objc());
                     panel.setDirectoryURL(url);
 
+                    if let Some(suggested_name) = suggested_name {
+                        let name_string = ns_string(&suggested_name);
+                        let _: () = msg_send![panel, setNameFieldStringValue: name_string];
+                    }
+
                     let done_tx = Cell::new(Some(done_tx));
                     let block = ConcreteBlock::new(move |response: NSModalResponse| {
                         let mut result = None;

crates/gpui/src/platform/test/platform.rs

@@ -336,6 +336,7 @@ impl Platform for TestPlatform {
     fn prompt_for_new_path(
         &self,
         directory: &std::path::Path,
+        _suggested_name: Option<&str>,
     ) -> oneshot::Receiver<Result<Option<std::path::PathBuf>>> {
         let (tx, rx) = oneshot::channel();
         self.background_executor()

crates/gpui/src/platform/windows/platform.rs

@@ -490,13 +490,18 @@ impl Platform for WindowsPlatform {
         rx
     }
 
-    fn prompt_for_new_path(&self, directory: &Path) -> Receiver<Result<Option<PathBuf>>> {
+    fn prompt_for_new_path(
+        &self,
+        directory: &Path,
+        suggested_name: Option<&str>,
+    ) -> Receiver<Result<Option<PathBuf>>> {
         let directory = directory.to_owned();
+        let suggested_name = suggested_name.map(|s| s.to_owned());
         let (tx, rx) = oneshot::channel();
         let window = self.find_current_active_window();
         self.foreground_executor()
             .spawn(async move {
-                let _ = tx.send(file_save_dialog(directory, window));
+                let _ = tx.send(file_save_dialog(directory, suggested_name, window));
             })
             .detach();
 
@@ -804,7 +809,11 @@ fn file_open_dialog(
     Ok(Some(paths))
 }
 
-fn file_save_dialog(directory: PathBuf, window: Option<HWND>) -> Result<Option<PathBuf>> {
+fn file_save_dialog(
+    directory: PathBuf,
+    suggested_name: Option<String>,
+    window: Option<HWND>,
+) -> Result<Option<PathBuf>> {
     let dialog: IFileSaveDialog = unsafe { CoCreateInstance(&FileSaveDialog, None, CLSCTX_ALL)? };
     if !directory.to_string_lossy().is_empty() {
         if let Some(full_path) = directory.canonicalize().log_err() {
@@ -815,6 +824,11 @@ fn file_save_dialog(directory: PathBuf, window: Option<HWND>) -> Result<Option<P
             unsafe { dialog.SetFolder(&path_item).log_err() };
         }
     }
+
+    if let Some(suggested_name) = suggested_name {
+        unsafe { dialog.SetFileName(&HSTRING::from(suggested_name)).log_err() };
+    }
+
     unsafe {
         dialog.SetFileTypes(&[Common::COMDLG_FILTERSPEC {
             pszName: windows::core::w!("All files"),