Add preview tabs (#9125)

This PR implements the preview tabs feature from VSCode.
More details and thanks for the head start of the implementation here
#6782.

Here is what I have observed from using the vscode implementation ([x]
-> already implemented):
- [x] Single click on project file opens tab as preview
- [x] Double click on item in project panel opens tab as permanent
- [x] Double click on the tab makes it permanent
- [x] Navigating away from the tab makes the tab permanent and the new
tab is shown as preview (e.g. GoToReference)
- [x] Existing preview tab is reused when opening a new tab
- [x] Dragging tab to the same/another panel makes the tab permanent
- [x] Opening a tab from the file finder makes the tab permanent
- [x] Editing a preview tab will make the tab permanent
- [x] Using the space key in the project panel opens the tab as preview
- [x] Handle navigation history correctly (restore a preview tab as
preview as well)
- [x] Restore preview tabs after restarting
- [x] Support opening files from file finder in preview mode (vscode:
"Enable Preview From Quick Open")
 
I need to do some more testing of the vscode implementation, there might
be other behaviors/workflows which im not aware of that open an item as
preview/make them permanent.

Showcase:


https://github.com/zed-industries/zed/assets/53836821/9be16515-c740-4905-bea1-88871112ef86


TODOs
- [x] Provide `enable_preview_tabs` setting
- [x] Write some tests
- [x] How should we handle this in collaboration mode (have not tested
the behavior so far)
- [x] Keyboard driven usage (probably need workspace commands)
- [x] Register `TogglePreviewTab` only when setting enabled?
- [x] Render preview tabs in tab switcher as italic
- [x] Render preview tabs in image viewer as italic
- [x] Should this be enabled by default (it is the default behavior in
VSCode)?
- [x] Docs

Future improvements (out of scope for now):
- Support preview mode for find all references and possibly other
multibuffers (VSCode: "Enable Preview From Code Navigation")


Release Notes:

- Added preview tabs
([#4922](https://github.com/zed-industries/zed/issues/4922)).

---------

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/workspace/src/workspace.rs

@@ -32,7 +32,10 @@ use gpui::{
     LayoutId, ManagedView, Model, ModelContext, PathPromptOptions, Point, PromptLevel, Render,
     Size, Subscription, Task, View, WeakView, WindowHandle, WindowOptions,
 };
-use item::{FollowableItem, FollowableItemHandle, Item, ItemHandle, ItemSettings, ProjectItem};
+use item::{
+    FollowableItem, FollowableItemHandle, Item, ItemHandle, ItemSettings, PreviewTabsSettings,
+    ProjectItem,
+};
 use itertools::Itertools;
 use language::{LanguageRegistry, Rope};
 use lazy_static::lazy_static;
@@ -261,6 +264,7 @@ impl Column for WorkspaceId {
 pub fn init_settings(cx: &mut AppContext) {
     WorkspaceSettings::register(cx);
     ItemSettings::register(cx);
+    PreviewTabsSettings::register(cx);
     TabBarSettings::register(cx);
 }
 
@@ -1142,7 +1146,13 @@ impl Workspace {
                     })?;
 
                     pane.update(&mut cx, |pane, cx| {
-                        let item = pane.open_item(project_entry_id, true, cx, build_item);
+                        let item = pane.open_item(
+                            project_entry_id,
+                            true,
+                            entry.is_preview,
+                            cx,
+                            build_item,
+                        );
                         navigated |= Some(item.item_id()) != prev_active_item_id;
                         pane.nav_history_mut().set_mode(NavigationMode::Normal);
                         if let Some(data) = entry.data {
@@ -2066,6 +2076,17 @@ impl Workspace {
         pane: Option<WeakView<Pane>>,
         focus_item: bool,
         cx: &mut WindowContext,
+    ) -> Task<Result<Box<dyn ItemHandle>, anyhow::Error>> {
+        self.open_path_preview(path, pane, focus_item, false, cx)
+    }
+
+    pub fn open_path_preview(
+        &mut self,
+        path: impl Into<ProjectPath>,
+        pane: Option<WeakView<Pane>>,
+        focus_item: bool,
+        allow_preview: bool,
+        cx: &mut WindowContext,
     ) -> Task<Result<Box<dyn ItemHandle>, anyhow::Error>> {
         let pane = pane.unwrap_or_else(|| {
             self.last_active_center_pane.clone().unwrap_or_else(|| {
@@ -2080,7 +2101,7 @@ impl Workspace {
         cx.spawn(move |mut cx| async move {
             let (project_entry_id, build_item) = task.await?;
             pane.update(&mut cx, |pane, cx| {
-                pane.open_item(project_entry_id, focus_item, cx, build_item)
+                pane.open_item(project_entry_id, focus_item, allow_preview, cx, build_item)
             })
         })
     }
@@ -2089,6 +2110,15 @@ impl Workspace {
         &mut self,
         path: impl Into<ProjectPath>,
         cx: &mut ViewContext<Self>,
+    ) -> Task<Result<Box<dyn ItemHandle>, anyhow::Error>> {
+        self.split_path_preview(path, false, cx)
+    }
+
+    pub fn split_path_preview(
+        &mut self,
+        path: impl Into<ProjectPath>,
+        allow_preview: bool,
+        cx: &mut ViewContext<Self>,
     ) -> Task<Result<Box<dyn ItemHandle>, anyhow::Error>> {
         let pane = self.last_active_center_pane.clone().unwrap_or_else(|| {
             self.panes
@@ -2110,7 +2140,7 @@ impl Workspace {
                 let pane = pane.upgrade()?;
                 let new_pane = this.split_pane(pane, SplitDirection::Right, cx);
                 new_pane.update(cx, |new_pane, cx| {
-                    Some(new_pane.open_item(project_entry_id, true, cx, build_item))
+                    Some(new_pane.open_item(project_entry_id, true, allow_preview, cx, build_item))
                 })
             })
             .map(|option| option.ok_or_else(|| anyhow!("pane was dropped")))?
@@ -2155,6 +2185,9 @@ impl Workspace {
         }
 
         let item = cx.new_view(|cx| T::for_project_item(self.project().clone(), project_item, cx));
+        pane.update(cx, |pane, cx| {
+            pane.set_preview_item_id(Some(item.item_id()), cx)
+        });
         self.add_item(pane, Box::new(item.clone()), cx);
         item
     }
@@ -2536,7 +2569,7 @@ impl Workspace {
         if source != destination {
             // Close item from previous pane
             source.update(cx, |source, cx| {
-                source.remove_item(item_ix, false, cx);
+                source.remove_item(item_ix, false, true, cx);
             });
         }
 
@@ -3408,6 +3441,7 @@ impl Workspace {
                                 kind: Arc::from(item_handle.serialized_item_kind()?),
                                 item_id: item_handle.item_id().as_u64(),
                                 active: Some(item_handle.item_id()) == active_item_id,
+                                preview: pane.is_active_preview_item(item_handle.item_id()),
                             })
                         })
                         .collect::<Vec<_>>(),