ptvsd not detecting symlink and setting unverified breakpoints

[DonJayamanne]

From @yajo on July 3, 2017 9:55

Environment data

VS Code version: 1.13.1
Python Extension version: 0.6.7
Python Version: 2.7
OS and version: Fedora 25, connecting to a dockerized Debian 8

Actual behavior

When localRoot and remoteRoot correctly match, but Python loads addons from a symlinked path, that is not detected and breakpoints become unverified. As such, I cannot step through the code normally.

Expected behavior

ptvsd should detect when the code is reached, either directly or from a symlinked path.

Steps to reproduce:

• Create a project and create a python file called mytest.py:

  def somemethod():
      pass

• From VSCode add a breakpoint inside somemethod().

• Create a Dockerfile like:

  FROM python:2.7-alpine
  RUN pip install --no-cache ptvsd==3.0.0
  RUN mkdir -p /src /dst/modules
  RUN touch /dst/modules/__init__.py
  RUN ln -s /src/mytest.py /dst/modules/
  RUN echo 'from .modules.mytest import somemethod; somemethod()' > /dst/importer.py
  CMD python -m ptvsd -s my_secret -p 6899 --wait /dst/importer.py

• Run the docker environment mounting your code in /src:

  docker build --tag test .
  docker run -it --rm -v $(pwd):/src -p 127.0.0.1:6899:6899 test
  

• Connect from VSCode pressing F5 (check launch.json below).

• You will see that vscode debugs, but the breakpoint appears as unverified, and you are not able to properly debug.

Settings

Your launch.json (if dealing with debugger issues):

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Run and debug",
            "type": "python",
            "request": "attach",
            "localRoot": "${workspaceRoot}",
            "remoteRoot": "/src",
            "port": 6899,
            "secret": "my_secret",
            "host": "localhost"
        }
    ]
}

Your settings.json:

{
    "python.formatting.provider": "yapf"
}

Logs

Output from Python output panel: nothing relevant.

Output from Console window (Help->Developer Tools menu): Nothing relevant.

Copied from original issue: DonJayamanne/pythonVSCode#1065

[DonJayamanne]

@yajo

You will see that vscode debugs

Does the debugger stop at the breakpoints?

I've tried the docker sample, but I'm getting the following error:

ValueError, Attempted relative import in non-package
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/runpy.py", line 174, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/local/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/usr/local/lib/python2.7/site-packages/ptvsd/__main__.py", line 57, in <module>
    exec_file(script_argv[0], {'__name__': '__main__'})
  File "/usr/local/lib/python2.7/site-packages/ptvsd/visualstudio_py_util.py", line 119, in exec_file
    exec_code(code, file, global_variables)
  File "/usr/local/lib/python2.7/site-packages/ptvsd/visualstudio_py_util.py", line 95, in exec_code
    exec(code_obj, global_variables)
  File "/dst/importer.py", line 1, in <module>
    from .modules.mytest import somemethod; somemethod()
ValueError: Attempted relative import in non-package

[yajo]

Thanks @DonJayamanne, I think I overcomplicated the example, let me reword it.

Prepare it

1. Use the same launch.json as before.

2. Change the Dockerfile to:

   FROM python:alpine
   RUN pip install --no-cache ptvsd==3.0.0
   RUN mkdir /src /dst
   COPY mytest.py /src/
   RUN ln -s /src/* /dst/

3. Change mytest.py to:

   def somemethod(greetings):
       print(greetings)
   
   
   somemethod("Hello")

4. Set an interruption point at this file's line 2 (the print statement).

5. Build the image: docker image build --tag test .

Run it from the real path

1. Execute:

    docker container run -it --rm -v $(pwd):/src:z -p 127.0.0.1:6899:6899 test python -m ptvsd -s my_secret -p 6899 --wait /src/mytest.py
   

2. Press F5

3. You can see that the debugger more or less works, apart from the fact that the breakpoint appears as unverified:

Run it from the symlinked path

1. Execute:

    docker container run -it --rm -v $(pwd):/src:z -p 127.0.0.1:6899:6899 test python -m ptvsd -s my_secret -p 6899 --wait /dst/mytest.py
   

2. Press F5

3. Some problems appear:

4. Go to the interactive shell, type greetings and press Enter. Some problems disappear, others appear:

5. Type greetings again and press Enter. Some problems disappear:

Summary

So, as you can see, remotely debugging with a properly configured file results in unverified breakpoints, I dunno why.

But if the remote file is being executed through a symlink, which is something I find myself doing quite often in the Docker world, the problems become bigger and more unstable.

I hope you understand better now 😊