editor: Prevent panic in lsp_symbols_at_cursor with diff hunks handling (#51077)

Fixes ZED-5M9

No test as I couldn't quite reproduce this, as the cause is mostly a
guess

Release Notes:

- Fixed a panic in `lsp_symbols_at_cursor` when dealing with diff hunks

crates/auto_update/src/auto_update.rs

@@ -212,18 +212,10 @@ pub fn init(client: Arc<Client>, cx: &mut App) {
 }
 
 pub fn check(_: &Check, window: &mut Window, cx: &mut App) {
-    if let Some(message) = option_env!("ZED_UPDATE_EXPLANATION") {
-        drop(window.prompt(
-            gpui::PromptLevel::Info,
-            "Zed was installed via a package manager.",
-            Some(message),
-            &["Ok"],
-            cx,
-        ));
-        return;
-    }
-
-    if let Ok(message) = env::var("ZED_UPDATE_EXPLANATION") {
+    if let Some(message) = option_env!("ZED_UPDATE_EXPLANATION")
+        .map(ToOwned::to_owned)
+        .or_else(|| env::var("ZED_UPDATE_EXPLANATION").ok())
+    {
         drop(window.prompt(
             gpui::PromptLevel::Info,
             "Zed was installed via a package manager.",

crates/editor/src/document_symbols.rs

@@ -77,6 +77,9 @@ impl Editor {
         let excerpt = multi_buffer_snapshot.excerpt_containing(cursor..cursor)?;
         let excerpt_id = excerpt.id();
         let buffer_id = excerpt.buffer_id();
+        if Some(buffer_id) != cursor.text_anchor.buffer_id {
+            return None;
+        }
         let buffer = self.buffer.read(cx).buffer(buffer_id)?;
         let buffer_snapshot = buffer.read(cx).snapshot();
         let cursor_text_anchor = cursor.text_anchor;

crates/rope/src/rope.rs

@@ -693,16 +693,21 @@ impl<'a> Cursor<'a> {
     }
 
     pub fn seek_forward(&mut self, end_offset: usize) {
-        debug_assert!(end_offset >= self.offset);
+        assert!(
+            end_offset >= self.offset,
+            "cannot seek backward from {} to {}",
+            self.offset,
+            end_offset
+        );
 
         self.chunks.seek_forward(&end_offset, Bias::Right);
         self.offset = end_offset;
     }
 
     pub fn slice(&mut self, end_offset: usize) -> Rope {
-        debug_assert!(
+        assert!(
             end_offset >= self.offset,
-            "cannot slice backwards from {} to {}",
+            "cannot slice backward from {} to {}",
             self.offset,
             end_offset
         );
@@ -730,7 +735,12 @@ impl<'a> Cursor<'a> {
     }
 
     pub fn summary<D: TextDimension>(&mut self, end_offset: usize) -> D {
-        debug_assert!(end_offset >= self.offset);
+        assert!(
+            end_offset >= self.offset,
+            "cannot summarize backward from {} to {}",
+            self.offset,
+            end_offset
+        );
 
         let mut summary = D::zero(());
         if let Some(start_chunk) = self.chunks.item() {