Fix LogDrawer line accumulation causing slowdown over time

Author: davidfstr

RELEASE_NOTES.md

@@ -36,6 +36,10 @@ Release Notes ⋮
           otherwise. See <doc/model_durability_and_atomicity.md> for details.
         * Failed transactions are now explicitly rolled back correctly.
 
+* Performance improvements
+    * The log drawer no longer slows down over time when many lines are written.
+      Old lines are automatically trimmed once the log exceeds 5,000 lines.
+
 * Shell changes
     * `Resource.delete()` and `ResourceRevision.delete()` now are asynchronous
       rather than synchronous, returning a `Future` to track completion.

src/crystal/tests/ui/main_window/test_log_drawer.py

@@ -1,11 +1,14 @@
 from collections.abc import AsyncIterator
-from contextlib import asynccontextmanager
+from contextlib import asynccontextmanager, redirect_stdout
 from crystal.server import get_request_url
+from crystal.tests.util.asserts import assertEqual
 from crystal.tests.util.server import assert_does_open_webbrowser_to, extracted_project
 from crystal.tests.util.windows import MainWindow, OpenOrCreateDialog
 from crystal.ui.log_drawer import LogDrawer
 from crystal.util.controls import click_button, TreeItem
+from io import StringIO
 from unittest import skip
+from unittest.mock import patch
 import wx
 from wx.richtext import RichTextCtrl
 
@@ -65,6 +68,36 @@ def test_always_displays_vertical_scrollbar_and_never_displays_horizontal_scroll
     pass
 
 
+async def test_when_write_many_lines_to_writer_beyond_max_then_leading_lines_trimmed() -> None:
+    MAX_LINE_COUNT = 50
+    with patch('crystal.ui.log_drawer._MAX_LINE_COUNT', MAX_LINE_COUNT):
+        async with _log_drawer_visible() as (mw, log_drawer):
+            textarea = log_drawer._textarea
+            writer = log_drawer.writer
+
+            # Count lines already present (from server startup banner)
+            initial_line_count = textarea.GetNumberOfLines()
+
+            # Write lines until we reach exactly MAX_LINE_COUNT
+            lines_to_add = MAX_LINE_COUNT - initial_line_count
+            with redirect_stdout(StringIO()):
+                for i in range(lines_to_add):
+                    writer.write(f'line {i}\n')
+            assertEqual(MAX_LINE_COUNT, textarea.GetNumberOfLines())
+
+            # Write one more line, which should cause the leading line to be trimmed
+            final_line_text = 'this is the final line'
+            with redirect_stdout(StringIO()):
+                writer.write(f'{final_line_text}\n')
+            assertEqual(MAX_LINE_COUNT, textarea.GetNumberOfLines(),
+                'Line count should still be MAX_LINE_COUNT after trimming')
+
+            # Verify the last line of content is the one we just wrote
+            last_content_line = textarea.GetLineText(MAX_LINE_COUNT - 2)
+            assertEqual(final_line_text, last_content_line,
+                'Last content line should be the final line we wrote')
+
+
 # === Test: Drag or Double-Click Sash ===
 
 @skip('not yet automated')

src/crystal/ui/log_drawer.py

@@ -35,6 +35,7 @@ def _hexcolor_to_color(hexcolor: str) -> wx.Colour:
     (cli.TERMINAL_FG_PURPLE, _hexcolor_to_color('#D43BD2')),
 ])  # type: dict[str, wx.Colour]
 _RESET_CODE = cli.TERMINAL_RESET
+_MAX_LINE_COUNT = 5000  # prevent unbounded growth over time
 
 
 # TODO: Avoid inheriting directly from wx.Frame because doing so
@@ -476,6 +477,13 @@ def fg_task() -> None:
                         #       from any text copied (or cut) from the text area.
                         textarea.WriteText('\u200b')  # zero-width space
 
+            # Trim leading lines if the total exceeds the maximum
+            line_count = textarea.GetNumberOfLines()
+            if line_count > _MAX_LINE_COUNT:
+                lines_to_remove = line_count - _MAX_LINE_COUNT
+                end_of_removed = textarea.XYToPosition(0, lines_to_remove)
+                textarea.Remove(0, end_of_removed)
+            
             if textarea_was_scrolled_to_bottom:
                 self._drawer._scroll_to_bottom()
         fg_call_later(fg_task)