editor: Fix showing completion list with selection does not include the selection (#57405)

Fix the completion list not showing the current selection when you
execute `editor: show completions`, the stated reason by comment before
is that if you are in a tabstop snippet already it wont give you the
correct options. So my change is to just check if you are in such a
snippet and if not give the new desired behavior.

before:


https://github.com/user-attachments/assets/1b2f3594-7361-4636-9ef3-f8c9419faa26

after:


https://github.com/user-attachments/assets/1be35582-464a-40f3-b6be-ee74f9961796


Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Closes #57386

Release Notes:

- editor: include text from selection in completion list.

---------

Co-authored-by: Smit Barmase <heysmitbarmase@gmail.com>

crates/editor/src/completions.rs

@@ -266,14 +266,20 @@ impl Editor {
 
         let multibuffer_snapshot = self.buffer.read(cx).read(cx);
 
-        // Typically `start` == `end`, but with snippet tabstop choices the default choice is
-        // inserted and selected. To handle that case, the start of the selection is used so that
-        // the menu starts with all choices.
-        let position = self
-            .selections
-            .newest_anchor()
-            .start
-            .bias_right(&multibuffer_snapshot);
+        let is_showing_snippet_choices = matches!(
+            completions_source,
+            Some(CompletionsMenuSource::SnippetChoices)
+        );
+
+        let anchor = self.selections.newest_anchor();
+        let position = if is_showing_snippet_choices {
+            // Typically `start` == `end`, but with snippet tabstop choices the default choice is
+            // inserted and selected. To handle that case, the start of the selection is used so that
+            // the menu starts with all choices.
+            anchor.start.bias_right(&multibuffer_snapshot)
+        } else {
+            anchor.head().bias_right(&multibuffer_snapshot)
+        };
 
         if position.diff_base_anchor().is_some() {
             return;
@@ -315,7 +321,7 @@ impl Editor {
 
         // Hide the current completions menu when query is empty. Without this, cached
         // completions from before the trigger char may be reused (#32774).
-        if query.is_none() && menu_is_open {
+        if query.is_none() && menu_is_open && !is_showing_snippet_choices {
             self.hide_context_menu(window, cx);
         }
 

crates/editor/src/editor_tests.rs

@@ -13732,6 +13732,49 @@ async fn test_snippet_placeholder_choices(cx: &mut TestAppContext) {
     });
 }
 
+#[gpui::test]
+async fn test_snippet_choices_menu_survives_completion_refresh(cx: &mut TestAppContext) {
+    init_test(cx, |_| {});
+
+    let (text, insertion_ranges) = marked_text_ranges(
+        indoc! {"
+            ˇ
+        "},
+        false,
+    );
+
+    let buffer = cx.update(|cx| MultiBuffer::build_simple(&text, cx));
+    let (editor, cx) = cx.add_window_view(|window, cx| build_editor(buffer, window, cx));
+
+    _ = editor.update_in(cx, |editor, window, cx| {
+        let snippet = Snippet::parse("type ${1|i32,u32|} = $2").unwrap();
+
+        editor
+            .insert_snippet(
+                &insertion_ranges
+                    .iter()
+                    .map(|range| MultiBufferOffset(range.start)..MultiBufferOffset(range.end))
+                    .collect::<Vec<_>>(),
+                snippet,
+                window,
+                cx,
+            )
+            .unwrap();
+
+        assert!(
+            editor.context_menu_visible(),
+            "Snippet choices menu should be visible after inserting the choice tabstop"
+        );
+
+        editor.open_or_update_completions_menu(None, None, false, window, cx);
+
+        assert!(
+            editor.context_menu_visible(),
+            "Snippet choices menu should remain visible after a completion refresh with an empty query"
+        );
+    });
+}
+
 #[gpui::test]
 async fn test_snippet_tabstop_navigation_with_placeholders(cx: &mut TestAppContext) {
     init_test(cx, |_| {});
@@ -18359,6 +18402,58 @@ async fn test_word_completions_continue_on_typing(cx: &mut TestAppContext) {
     });
 }
 
+#[gpui::test]
+async fn test_completions_use_selection_head(cx: &mut TestAppContext) {
+    init_test(cx, |language_settings| {
+        language_settings.defaults.completions = Some(CompletionSettingsContent {
+            words: Some(WordsCompletionMode::Disabled),
+            words_min_length: Some(0),
+            lsp_insert_mode: Some(LspInsertMode::Insert),
+            ..Default::default()
+        });
+    });
+
+    let mut cx = EditorLspTestContext::new_rust(
+        lsp::ServerCapabilities {
+            completion_provider: Some(lsp::CompletionOptions::default()),
+            ..lsp::ServerCapabilities::default()
+        },
+        cx,
+    )
+    .await;
+
+    let _completion_requests_handler =
+        cx.lsp
+            .server
+            .on_request::<lsp::request::Completion, _, _>(move |_, _| async move {
+                panic!("LSP completions should not be queried when dealing with word completions")
+            });
+
+    cx.set_state(indoc! {"«applˇ»
+        applepie
+        banana
+        cherry
+    "});
+    cx.update_editor(|editor, window, cx| {
+        editor.show_word_completions(&ShowWordCompletions, window, cx);
+    });
+    cx.executor().run_until_parked();
+    cx.condition(|editor, _| editor.context_menu_visible())
+        .await;
+    cx.update_editor(|editor, _, _| {
+        if let Some(CodeContextMenu::Completions(menu)) = editor.context_menu.borrow_mut().as_ref()
+        {
+            assert_eq!(
+                completion_menu_entries(menu),
+                &["applepie"],
+                "Completion query should use the selection head (`appl`), filtering to words with that prefix"
+            );
+        } else {
+            panic!("expected completion menu to be open");
+        }
+    });
+}
+
 #[gpui::test]
 async fn test_word_completions_usually_skip_digits(cx: &mut TestAppContext) {
     init_test(cx, |language_settings| {