Could not stop at breakpoint when pathMappings.localRoot has slash

[formulahendry]

Environment data

• PTVSD version: 4.1.1a11
• OS and version: Windows 10
• Python version (& distribution if applicable, e.g. Anaconda): Python2
• Using VS Code or Visual Studio: VS Code

Actual behavior

Could not map file correctly to stop at breakpoint when pathMappings.localRoot has slash

Steps to reproduce:

1. git clone https://github.com/formulahendry/python-amd64-debug.git
2. docker build --rm -f Dockerfile.amd64.debug -t python-amd64-debug:latest .
3. docker run -d -p 4000:3000 --name python-test python-amd64-debug:latest
4. Attach the python code with the 3 configurations in launch.json

{
            "name": "Python Experimental: Attach (working)",
            "type": "pythonExperimental",
            "request": "attach",
            "port": 4000,
            "host": "localhost",
            "pathMappings": [{
                "localRoot": "${workspaceFolder}", // Local root  (where source and debugger running)
                "remoteRoot": "/app" // Remote root (where remote code is running)
            }]
        },
        {
            "name": "Python Experimental: Attach (sub folder) (working)",
            "type": "pythonExperimental",
            "request": "attach",
            "port": 4000,
            "host": "localhost",
            "pathMappings": [{
                "localRoot": "${workspaceFolder}\\test", // Local root  (where source and debugger running)
                "remoteRoot": "/app" // Remote root (where remote code is running)
            }]
        },
        {
            "name": "Python Experimental: Attach (sub folder) (not working)",
            "type": "pythonExperimental",
            "request": "attach",
            "port": 4000,
            "host": "localhost",
            "pathMappings": [{
                "localRoot": "${workspaceFolder}/test", // Local root  (where source and debugger running)
                "remoteRoot": "/app" // Remote root (where remote code is running)
            }]
        }

5. The Python Experimental: Attach (sub folder) (not working) is not working, while other two work
   

[brettcannon]

Our CTI also had an issue with ${workspaceFolder} where it ended up being translated to /C:/test/temotedebug.py (note the leading slash and path separators). When she set localRoot to C:\\test\\ it apparently worked. (She was trying remote debugging from Windows to Linux.)