Replace removed pkgutil.get_loader with importlib.util.find_spec in get_fullname (#1998)

* Initial plan

* Fix get_fullname to use importlib.util.find_spec instead of removed pkgutil.get_loader

pkgutil.get_loader() was removed in Python 3.14, causing subprocess
module execution to fail with "No module named" when subProcess: true.
Replace with importlib.util.find_spec() which is the recommended
replacement and works across all supported Python versions.

Co-authored-by: rchiodo <19672699+rchiodo@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: rchiodo <19672699+rchiodo@users.noreply.github.com>

Author: Copilot

src/debugpy/_vendored/pydevd/pydevd_file_utils.py

@@ -966,17 +966,14 @@ def get_abs_path_real_path_and_base_from_frame(frame, NORM_PATHS_AND_BASE_CONTAI
 
 
 def get_fullname(mod_name):
-    import pkgutil
-
     try:
-        loader = pkgutil.get_loader(mod_name)
-    except:
-        return None
-    if loader is not None:
-        for attr in ("get_filename", "_get_filename"):
-            meth = getattr(loader, attr, None)
-            if meth is not None:
-                return meth(mod_name)
+        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
 
 

src/debugpy/_vendored/pydevd/tests_python/test_convert_utilities.py

@@ -560,3 +560,34 @@ def test_mapping_conflict_to_server():
     {"remoteRoot": "/var/home/p3", "localRoot": "/opt/v2/path"},
     {"remoteRoot": "/var/home/p4", "localRoot": "/opt/v2/pathsomething"},
 ]
+
+
+def test_get_fullname(tmp_path):
+    """Test that get_fullname correctly resolves module names to file paths.
+
+    This is a regression test for the fix that replaced pkgutil.get_loader
+    (removed in Python 3.14) with importlib.util.find_spec.
+    """
+    from pydevd_file_utils import get_fullname
+
+    # Create a temporary module file
+    mod_file = tmp_path / "my_test_mod.py"
+    mod_file.write_text("x = 1\n")
+
+    # Add tmp_path to sys.path so the module can be found
+    sys.path.insert(0, str(tmp_path))
+    try:
+        result = get_fullname("my_test_mod")
+        assert result is not None
+        assert result.endswith("my_test_mod.py")
+
+        # Non-existent module should return None
+        result = get_fullname("nonexistent_module_xyz_12345")
+        assert result is None
+
+        # A stdlib package with __init__.py should be found
+        result = get_fullname("json")
+        assert result is not None
+        assert result.endswith("__init__.py")
+    finally:
+        sys.path.remove(str(tmp_path))