Fix local nbextensions path resolution for kernels launched from local kernelspec (#16886)

* Initial plan

* Fix: Add support for startUsingLocalKernelSpec in NbExtensionsPathProvider

Co-authored-by: DonJayamanne <[email protected]>

* Fix formatting: Remove trailing whitespace from comment

Co-authored-by: DonJayamanne <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: DonJayamanne <[email protected]>

Author: Copilot

src/notebooks/controllers/ipywidgets/scriptSourceProvider/nbExtensionsPathProvider.node.ts

@@ -25,6 +25,20 @@ export class NbExtensionsPathProvider implements INbExtensionsPathProvider {
                 }
                 return Uri.joinPath(Uri.file(sysPrefix), 'share', 'jupyter');
             }
+            case 'startUsingLocalKernelSpec': {
+                // If the local kernelspec has an associated Python interpreter,
+                // use the same logic as startUsingPythonInterpreter
+                if (kernel.kernelConnectionMetadata.interpreter) {
+                    const sysPrefix = await getSysPrefix(kernel.kernelConnectionMetadata.interpreter);
+                    if (!sysPrefix) {
+                        return;
+                    }
+                    return Uri.joinPath(Uri.file(sysPrefix), 'share', 'jupyter');
+                }
+                // If no interpreter, we haven't come across scenarios with non-python kernels that use widgets
+                // & have custom widget sources. If we do, we can implement that as we come across them.
+                return;
+            }
             default: {
                 // We haven't come across scenarios with non-python kernels that use widgets
                 // & have custom widget sources. If we do, we can implement that as we come across them.

src/notebooks/controllers/ipywidgets/scriptSourceProvider/nbExtensionsPathProvider.unit.test.ts

@@ -36,6 +36,13 @@ import { dispose } from '../../../../platform/common/utils/lifecycle';
             id: 'interpreterId'
         } as any
     });
+    const localKernelSpecWithPythonInterpreter = LocalKernelSpecConnectionMetadata.create({
+        id: 'localKernelSpecWithPythonInterpreter',
+        kernelSpec: mock<IJupyterKernelSpec>(),
+        interpreter: {
+            id: 'interpreterId'
+        } as any
+    });
     const serverProviderHandle = { handle: 'handle', id: 'id', extensionId: '' };
     const remoteKernelSpec = RemoteKernelSpecConnectionMetadata.create({
         id: '',
@@ -82,6 +89,15 @@ import { dispose } from '../../../../platform/common/utils/lifecycle';
                 assert.strictEqual(baseUrl?.toString(), Uri.file(path.join(__dirname, 'share', 'jupyter')).toString());
             }
         });
+        test('Returns base url for local kernelspec with python interpreter', async () => {
+            when(kernel.kernelConnectionMetadata).thenReturn(localKernelSpecWithPythonInterpreter);
+            const baseUrl = await provider.getNbExtensionsParentPath(instance(kernel));
+            if (isWeb) {
+                assert.isUndefined(baseUrl);
+            } else {
+                assert.strictEqual(baseUrl?.toString(), Uri.file(path.join(__dirname, 'share', 'jupyter')).toString());
+            }
+        });
         test('Returns base url for remote kernelspec', async () => {
             when(kernel.kernelConnectionMetadata).thenReturn(remoteKernelSpec);
             const baseUrl = await provider.getNbExtensionsParentPath(instance(kernel));