ptvsd import suppresses coverage reporting

[rjungwirth]

Environment data

• PTVSD version: 4.3.2
• OS and version: Mac OS X 10.14.6
• Python version (& distribution if applicable, e.g. Anaconda): python 3.7.3 + coverage-5.0.4
• Using VS Code or Visual Studio: N/A

Actual behavior

import ptvsd module suppresses coverage reporting for all execution after import

Expected behavior

importing ptvsd should not cause coverage reporting to be supressed

Steps to reproduce:

1. run this bash script:

#!/usr/bin/env bash
rm -rf _venv
python3 -m venv _venv
./_venv/bin/pip3 install --upgrade pip
./_venv/bin/pip3 install coverage ptvsd
cat >foo_test.py<<EOF
import sys
if len(sys.argv) > 1: import ptvsd
def do_something(x):
    return x
do_something(5)
EOF
_venv/bin/coverage run --omit=_venv/* foo_test.py
if $(_venv/bin/coverage report | fgrep foo_test.py | fgrep -q '100%'); then echo 'NO IMPORT PTVSD SUCCESS'; else echo 'NO IMPORT PTVSD FAILURE ';fi
_venv/bin/coverage run --omit=_venv/* foo_test.py 1
if $(_venv/bin/coverage report | fgrep foo_test.py | fgrep -q '100%'); then echo 'IMPORT PTVSD SUCCESS'; else echo 'IMPORT PTVSD FAILURE';fi

observe:

test case 1 succeeds (no importing PTVSD == full coverage reporting)

test case 2 fails: importing PTVSD causes coverage reporting to stop for all subsequent execution steps in script

[rjungwirth]

this is a big "gotcha"! Simply importing PTVSD suppresses code coverage regardless of whether you use the functionality or not.

Please add a note to the documentation so others don't waste their time figuring out what is wrong with their code!

[int19h]

This shouldn't be the case for ptvsd 5.x / debugpy anymore, since it doesn't import pydevd unless and until the module is actually used - merely importing it does nothing.