editor: Respect read_only in newline_below (#50804)

Turns out `Editor::newline_below` was not respecting the `read_only`
flag because it uses buffer.edit. `Editor::newline` and
`Editor::newline_above` behaved correctly because they used
`editor.edit` which ignores edits if `read_only` is true.

Added an early return if the editor is read only, also added it to
newline/newline_above for clarity.

Release Notes:

- Fixed an issue where newlines could be inserted into read-only editors

crates/editor/src/editor.rs

@@ -5088,6 +5088,10 @@ impl Editor {
     }
 
     pub fn newline(&mut self, _: &Newline, window: &mut Window, cx: &mut Context<Self>) {
+        if self.read_only(cx) {
+            return;
+        }
+
         self.hide_mouse_cursor(HideMouseCursorOrigin::TypingAction, cx);
         self.transact(window, cx, |this, window, cx| {
             let (edits_with_flags, selection_info): (Vec<_>, Vec<_>) = {
@@ -5309,6 +5313,10 @@ impl Editor {
     }
 
     pub fn newline_above(&mut self, _: &NewlineAbove, window: &mut Window, cx: &mut Context<Self>) {
+        if self.read_only(cx) {
+            return;
+        }
+
         self.hide_mouse_cursor(HideMouseCursorOrigin::TypingAction, cx);
 
         let buffer = self.buffer.read(cx);
@@ -5376,6 +5384,10 @@ impl Editor {
     }
 
     pub fn newline_below(&mut self, _: &NewlineBelow, window: &mut Window, cx: &mut Context<Self>) {
+        if self.read_only(cx) {
+            return;
+        }
+
         self.hide_mouse_cursor(HideMouseCursorOrigin::TypingAction, cx);
 
         let mut buffer_edits: HashMap<EntityId, (Entity<Buffer>, Vec<Point>)> = HashMap::default();

crates/editor/src/editor_tests.rs

@@ -3382,6 +3382,46 @@ async fn test_newline_below(cx: &mut TestAppContext) {
     "});
 }
 
+#[gpui::test]
+fn test_newline_respects_read_only(cx: &mut TestAppContext) {
+    init_test(cx, |_| {});
+
+    let editor = cx.add_window(|window, cx| {
+        let buffer = MultiBuffer::build_simple("aaaa\nbbbb\n", cx);
+        build_editor(buffer, window, cx)
+    });
+
+    _ = editor.update(cx, |editor, window, cx| {
+        editor.set_read_only(true);
+        editor.change_selections(SelectionEffects::no_scroll(), window, cx, |s| {
+            s.select_display_ranges([
+                DisplayPoint::new(DisplayRow(0), 2)..DisplayPoint::new(DisplayRow(0), 2)
+            ])
+        });
+
+        editor.newline(&Newline, window, cx);
+        assert_eq!(
+            editor.text(cx),
+            "aaaa\nbbbb\n",
+            "newline should not modify a read-only editor"
+        );
+
+        editor.newline_above(&NewlineAbove, window, cx);
+        assert_eq!(
+            editor.text(cx),
+            "aaaa\nbbbb\n",
+            "newline_above should not modify a read-only editor"
+        );
+
+        editor.newline_below(&NewlineBelow, window, cx);
+        assert_eq!(
+            editor.text(cx),
+            "aaaa\nbbbb\n",
+            "newline_below should not modify a read-only editor"
+        );
+    });
+}
+
 #[gpui::test]
 fn test_newline_below_multibuffer(cx: &mut TestAppContext) {
     init_test(cx, |_| {});