Fix CodeEditor annotations overwritten by Ace worker

[ghostiee-11]

Description

Fixes #7967

Since the Ace upgrade (v1.4.11 to v1.40.1 in #7874), explicitly setting annotations on a CodeEditor gets overwritten by Ace's background syntax-checking worker. The worker fires asynchronously after session.setMode() and calls session.setAnnotations() with its own results, wiping out user-set annotations.

I traced the issue to panel/models/ace.ts:

• _update_language() calls session.setMode() which spawns a worker that overwrites annotations
• There was no mechanism to prevent the worker from clobbering user annotations

The fix:

• When user annotations are set (non-empty), disable the Ace session worker with setUseWorker(false) so it cannot overwrite them
• When annotations are cleared back to empty, re-enable the worker so default syntax checking resumes
• Call _add_annotations() in _update_language() after setMode() so annotations persist across language/mode changes

Important ordering detail: setUseWorker(false) clears the session's annotations as a side effect, so the worker must be toggled before calling setAnnotations().

Known Limitations

When user annotations are set (non-empty), Ace's built-in syntax checking worker is disabled to prevent it from overwriting custom annotations. This means real-time syntax error/warning markers from Ace will not appear alongside user-set annotations. Syntax checking resumes automatically when annotations are cleared back to []. This matches the behavior of Panel < 1.7.0 where the annotations parameter gave users full control over the annotation system.

Reproducer (from the issue):

import panel as pn
pn.extension("codeeditor")

code = "test:\n- {a: 1, b: 2}\n- {c: 3, d: 4}\n- {e: 5, f: 6}\n"
editor = pn.widgets.CodeEditor(value=code, language="yaml", annotations=[])

def add_annotations(event):
    editor.annotations = [
        {"row": 1, "column": 0, "text": "a warning", "type": "warning"},
        {"row": 2, "column": 0, "text": "an error", "type": "error"},
    ]

def clear_annotations(event):
    editor.annotations = []

add_btn = pn.widgets.Button(name="Add Annotations", button_type="primary")
add_btn.on_click(add_annotations)
clear_btn = pn.widgets.Button(name="Clear Annotations", button_type="warning")
clear_btn.on_click(clear_annotations)

pn.Row(editor, pn.Column(add_btn, clear_btn)).servable()

Before fix (annotations never appear after clicking "Add Annotations"):

After fix (annotations appear and persist after clicking "Add Annotations"):

After fix (annotations cleared after clicking "Clear Annotations"):

How Has This Been Tested?

• All 4 existing test_codeeditor.py UI tests pass
• All 3 existing test_ace.py unit tests pass
• Added 6 new UI tests:
  • test_code_editor_annotations: sets annotations dynamically, verifies worker is disabled, checks persistence across multiple checkpoints, clears and verifies worker re-enables
  • test_code_editor_annotations_constructor: verifies constructor-provided annotations are applied, worker is disabled, and annotations persist
  • test_code_editor_annotations_persist_on_language_change: sets annotations then changes language, verifies annotations survive the mode/worker respawn
  • test_code_editor_annotations_replacement: replaces one set of annotations with another, verifies the new set is applied correctly
  • test_code_editor_annotations_persist_on_value_change: sets annotations then changes code value programmatically, verifies annotations survive
  • test_code_editor_worker_resumes_after_clear: full lifecycle test — verifies Ace's JS worker produces syntax errors on invalid code, user annotations override them (worker disabled), and after clearing the worker resumes producing its own annotations
• All annotation tests use multi-checkpoint stability assertions (5 checks x 200ms) instead of single hardcoded sleeps for CI robustness
• Manual testing with the reproducer above confirms annotations display correctly and are not overwritten

AI Disclosure

• This PR contains AI-generated content.
  • I have tested all AI-generated content in my PR.
  • I take responsibility for all AI-generated content in my PR.
    Tools: Claude, used to help scaffold the fix and tests after I identified the root cause.

Checklist

• Tests added and is passing

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.09%. Comparing base (f6dc8a7) to head (b60ffe7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #8505       +/-   ##
===========================================
+ Coverage   70.34%   86.09%   +15.75%     
===========================================
  Files         348      349        +1     
  Lines       55198    55292       +94     
===========================================
+ Hits        38828    47606     +8778     
+ Misses      16370     7686     -8684     

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[ghostiee-11]

Thanks for the merge and review!! 😊

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.