Allow server to configure its root

[thejcannon]

In the Pants project we're facing an issue where we can't set breakpoints on files when running some code, and it boils down to the remoteRoot being CWD but code is running in a tempr sandbox.

To give an overview of the workflow here:

• User tells pants to run their code and launch a debug server
• Pants creates a sandbox in /tmp/... with all the code laid out
• Pants launches the debug server (using debugpy) and waits for connection
  • CWD of the process is the user's code root
• User connects but since the remote root is configured as "." which isn't the tempdir breakpoints relative to the code root aren't loaded

You could say "OK, the user should be setting the pathMapping", which would be annoying at the least, but is ultimately impossible as the sandboxes (the tempdir) is ephemeral, fresh, and distinct per run.

I suspect what I really want is to allow the server to (somehow) specify it's "root" when being invoked (which in this case would be the sandbox tempdir)

[fabioz]

If paths are ephemeral and you can't pre-configure them to apply path mappings, maybe you could use an API which would collect the paths and runtime and set the mapping for the debugger?

See: #743 (comment) for how to do that.

[fabioz]

I was also thinking that maybe having the path mapping allow for environment variables set in the server could potentially be a solution here too (so, you could have an environment variable resolved in the server as a part of the path mapping resolution) -- note that this isn't implemented at this point.

[thejcannon]

so, you could have an environment variable resolved in the server as a part of the path mapping resolution

So that'd be relevant here?

debugpy/src/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_process_net_command_json.py

Line 322 in 4067700

if remote_root == '.':

[fabioz]

so, you could have an environment variable resolved in the server as a part of the path mapping resolution

So that'd be relevant here?

debugpy/src/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_process_net_command_json.py

Line 322 in 4067700

if remote_root == '.':

Yes.

[thejcannon]

See: #743 (comment) for how to do that.

Ah hey that works, thanks! I'd still advocate for a env var, as thats much easier.

[thejcannon]

OK I actually did something slightly different:

import debugpy._vendored.force_pydevd
from _pydevd_bundle.pydevd_process_net_command_json import PyDevJsonCommandProcessor
orig_resolve_remote_root = PyDevJsonCommandProcessor._resolve_remote_root

def patched_resolve_remote_root(self, local_root, remote_root):
    if remote_root == ".":
        remote_root = CHROOT
    return orig_resolve_remote_root(self, local_root, remote_root)

PyDevJsonCommandProcessor._resolve_remote_root = patched_resolve_remote_root

I didn't want to tell our users to omit pathMappings as that is the VS Code default. This way we assume "." means our sandbox root.