Replace removed pkgutil.get_loader with importlib.util.find_spec in get_fullname

[Copilot]

pkgutil.get_loader() was removed in Python 3.14, causing get_fullname() to silently return None for all module lookups. When subProcess: true, debugpy intercepts subprocess calls and uses get_fullname() to resolve -m <module> targets. The silent failure cascades to "No module named ..." for any single-file module run via subprocess.run([sys.executable, "-m", "mod"]).

Changes

• pydevd_file_utils.py: Replace pkgutil.get_loader() with importlib.util.find_spec(), checking spec.has_location to exclude built-in/frozen module origins (e.g. "built-in", "frozen") that aren't file paths
• test_convert_utilities.py: Add regression test for get_fullname() covering single-file modules, packages, and nonexistent modules

# Before (broken on 3.14+)
def get_fullname(mod_name):
    import pkgutil
    try:
        loader = pkgutil.get_loader(mod_name)  # AttributeError on 3.14
    except:
        return None
    ...

# After
def get_fullname(mod_name):
    try:
        import importlib.util
        spec = importlib.util.find_spec(mod_name)
        if spec is not None and spec.origin is not None and spec.has_location:
            return spec.origin
    except (ImportError, ModuleNotFoundError, ValueError):
        pass
    return None

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Unable to run a Python module in a subprocess when subProcess: true</issue_title>
<issue_description>The following script executes a Python module in a subprocess.

# main.py
import subprocess
import sys

subprocess.run([sys.executable, "-m", "sub"])

# sub.py
print("Hello, world!")

// launch.json
{
    "version": "0.2.0",
    "configurations": [
    
        {
            "name": "Python Debugger: Current File",
            "type": "debugpy",
            "request": "launch",
            "program": "${file}",
            "console": "integratedTerminal",
            "subProcess": true,
        }
    ]
}

Running this in the debugger with "subProcess": true fails:

bash-3.2$  cd /Users/pete/projects/subprocess_test ; /usr/bin/env /Users/pete/projects/subprocess_test/.venv/bin/python /Users/pete/.vscode/extensions/ms-python.debugpy-2025.18.0-darwin-arm64/bundled/libs/debugpy/adapter/../../debugpy/launcher 56894 -- /Users/pete/projects/subprocess_test/main.py 
No module named sub

Running it with "subProcess": false works as expected:

bash-3.2$  cd /Users/pete/projects/subprocess_test ; /usr/bin/env /Users/pete/projects/subprocess_test/.venv/bin/python /Users/pete/.vscode/extensions/ms-python.debugpy-2025.18.0-darwin-arm64/bundled/libs/debugpy/adapter/../../debugpy/launcher 57618 -- /Users/pete/projects/subprocess_test/main.py 
Hello, world!

OS: Darwin arm64 25.3.0
VSCode: 1.109.5 (Universal)
Python Debugger: 2025.18.0
Python: 3.14.2 (in a virtualenv)</issue_description>

<agent_instructions>I can reproduce this problem. You'll likely need to write a test that reproduces the issue and then add logging to debugpy to figure out why it can find the 'sub' module.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Unable to run a Python module in a subprocess when subProcess: true #1997

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