Do not add dependency css for theme packages.

The theme css bundler cannot handle dependency imports. Explicitly specifying the dependencies to ignore for built-in themes does not solve the problem when linking a local theme extension, as happens in the usage test with the “foo” extension.

buildutils/src/ensure-repo.ts

@@ -211,14 +211,6 @@ const SKIP_CSS: Dict<string[]> = {
     '@jupyterlab/cells',
     '@jupyterlab/notebook'
   ],
-  '@jupyterlab/theme-dark-extension': [
-    '@jupyterlab/application',
-    '@jupyterlab/apputils'
-  ],
-  '@jupyterlab/theme-light-extension': [
-    '@jupyterlab/application',
-    '@jupyterlab/apputils'
-  ],
   '@jupyterlab/ui-extension': ['@blueprintjs/icons']
 };
 
@@ -488,16 +480,19 @@ export async function ensureIntegrity(): Promise<boolean> {
       });
     }
 
-    Object.keys(deps).forEach(depName => {
-      // Bail for skipped imports and known extra styles.
-      if (skip.indexOf(depName) !== -1 || depName in cssData) {
-        return;
-      }
-      const depData = graph.getNodeData(depName);
-      if (typeof depData.style === 'string') {
-        cssData[depName] = [depData.style];
-      }
-    });
+    // Add dependency css if package is not a theme package
+    if (!(data.jupyterlab && data.jupyterlab.themePath)) {
+      Object.keys(deps).forEach(depName => {
+        // Bail for skipped imports and known extra styles.
+        if (skip.indexOf(depName) !== -1 || depName in cssData) {
+          return;
+        }
+        const depData = graph.getNodeData(depName);
+        if (typeof depData.style === 'string') {
+          cssData[depName] = [depData.style];
+        }
+      });
+    }
 
     // Get our CSS imports in dependency order.
     cssImports[name] = [];