TraitError: The 'synctex_command' trait expected a boolean, not the str 'synctex' (Python 3.13)

[X0bang]

Description

When attempting to use the SyncTeX feature (reverse search from PDF to source code, or forward search from code to PDF), the server returns a 500 Internal Server Error.

The backend logs reveal a TypeError caused by attempting to use a Boolean value (c.synctex_command) as a string in command construction.

Steps to Reproduce

1. Install jupyterlab-latex==4.3.0 in a Python 3.13 environment with JupyterLab 4.5.0
2. Open a valid .tex file in JupyterLab
3. Build the LaTeX file to generate the .pdf and .synctex.gz files
4. Right-click on the PDF preview and select "Scroll Editor to Page" (or Ctrl/Cmd + Click on the PDF)
5. Observe a "500 Internal Server Error" in the browser console

Expected Behavior

The editor should navigate to the corresponding line in the .tex file without errors.

Environment

• Operating System: Ubuntu 22.04 LTS
• Python Version: 3.13.9
• JupyterLab Version: 4.5.0
• jupyterlab-latex Version: 4.3.0
• Browser: Chrome 143

Error Logs

Primary Error

TypeError: sequence item 0: expected str instance, bool found
    at jupyterlab_latex/synctex.py:148, in run_synctex
    self.log.debug(f'jupyterlab-latex: run: {" ".join(cmd)} (CWD: {os.getcwd()})')

Full Traceback

```python [E 2025-12-12 01:35:28.536 SingleUserLabApp web:1934] Uncaught exception GET /user/username/latex/synctex/... Traceback (most recent call last): File ".../tornado/web.py", line 1848, in _execute result = await result File ".../tornado/gen.py", line 796, in run yielded = self.gen.throw(exc) File ".../jupyterlab_latex/synctex.py", line 197, in get out = yield self.run_synctex(cmd) File ".../tornado/gen.py", line 783, in run value = future.result() File ".../tornado/gen.py", line 239, in wrapper yielded = ctx_run(next, result) File ".../jupyterlab_latex/synctex.py", line 148, in run_synctex self.log.debug(f'jupyterlab-latex: run: {" ".join(cmd)} (CWD: {os.getcwd()})') TypeError: sequence item 0: expected str instance, bool found ```

Root Cause

The issue is in two methods in synctex.py:

1. build_synctex_edit_cmd (around line 85)
2. build_synctex_view_cmd (around line 100)

Both methods incorrectly use c.synctex_command (a Boolean trait) directly in the command tuple where a string is expected:

cmd = (
    c.synctex_command,  # ❌ This is a Boolean, not a string!
    'edit',  # or 'view'
    ...
)

When the code later tries to join this tuple as strings (line 148), it fails because the first element is False instead of 'synctex'.

Proposed Fix

Fix 1: In build_synctex_edit_cmd (around line 83-88)

Before:

cmd = (
    c.synctex_command,
    'edit',
    '-o',
    f'{pos["page"]}:{pos["x"]}:{pos["y"]}:{pdf_path}'
)

After:

cmd = (
    'synctex',  # ✅ Hardcode the command string
    'edit',
    '-o',
    f'{pos["page"]}:{pos["x"]}:{pos["y"]}:{pdf_path}'
)

Fix 2: In build_synctex_view_cmd (around line 98-104)

Before:

cmd = (
    c.synctex_command,
    'view',
    '-i',
    f'{pos["line"]}:{pos["column"]}:{tex_path}',
    '-o',
    f'{pdf_path}'
)

After:

cmd = (
    'synctex',  # ✅ Hardcode the command string
    'view',
    '-i',
    f'{pos["line"]}:{pos["column"]}:{tex_path}',
    '-o',
    f'{pdf_path}'
)

Alternative Solution

If c.synctex_command is intended to allow custom command paths, it should be changed to:

cmd = (
    str(c.synctex_command) if isinstance(c.synctex_command, str) else 'synctex',
    # ... rest of the command
)

If this approach looks reasonable, I'm happy to open a Pull Request with the fix.

[cmarmo]

Hi @X0bang this one has been fixed in #250.
But there is no released version after the bugfix, so you have to install the development version if you want the bug gone.

[cmarmo]

The new version is available
https://github.com/jupyterlab/jupyterlab-latex/releases/tag/v4.4.0