Ensure external resources are configured correctly on save (#2452)

* Ensure external resources are configured correctly on save

* Add test

panel/io/save.py

@@ -17,6 +17,7 @@
 from pyviz_comms import Comm
 
 from ..config import config
+from . import resources as resource_module
 from .embed import embed_state
 from .model import add_to_doc
 from .resources import BASE_TEMPLATE, DEFAULT_TITLE, Bundle, Resources
@@ -217,11 +218,14 @@ def save(panel, filename, title=None, resources=None, template=None,
 
     if resources is None:
         resources = CDN
+        mode = 'cdn'
     elif isinstance(resources, str):
         if resources.lower() == 'cdn':
             resources = CDN
+            mode = 'cdn'
         elif resources.lower() == 'inline':
             resources = INLINE
+            mode = 'inline'
         else:
             raise ValueError("Resources %r not recognized, specify one "
                              "of 'CDN' or 'INLINE'." % resources)
@@ -245,7 +249,13 @@ def save(panel, filename, title=None, resources=None, template=None,
 
     resources = Resources.from_bokeh(resources)
 
-    html = file_html(doc, resources, title, **kwargs)
+    # Set resource mode
+    old_mode = resource_module.RESOURCE_MODE
+    resource_module.RESOURCE_MODE = mode
+    try:
+        html = file_html(doc, resources, title, **kwargs)
+    finally:
+        resource_module.RESOURCE_MODE = old_mode
     if hasattr(filename, 'write'):
         if isinstance(filename, io.BytesIO):
             html = html.encode('utf-8')

panel/tests/io/test_save.py

@@ -0,0 +1,32 @@
+from io import StringIO
+
+from panel.pane import Vega
+from panel.models.vega import VegaPlot
+
+
+vega_example = {
+    'config': {
+        'mark': {'tooltip': None},
+        'view': {'height': 300, 'width': 400}
+    },
+    'data': {'values': [{'x': 'A', 'y': 5},
+                        {'x': 'B', 'y': 3},
+                        {'x': 'C', 'y': 6},
+                        {'x': 'D', 'y': 7},
+                        {'x': 'E', 'y': 2}]},
+    'mark': 'bar',
+    'encoding': {'x': {'type': 'ordinal', 'field': 'x'},
+                 'y': {'type': 'quantitative', 'field': 'y'}},
+    '$schema': 'https://vega.github.io/schema/vega-lite/v3.2.1.json'
+}
+
+
+def test_save_external():
+    sio = StringIO()
+    pane = Vega(vega_example)
+
+    pane.save(sio)
+    sio.seek(0)
+    html = sio.read()
+    for js in VegaPlot.__javascript_raw__:
+        assert js in html