Vega extension not loading in subdirectory

[malramsay64]

Description

When inside a subdirectory the paths to a Vega file don't include the directory parts of the path of the current notebook. That is the download path is

localhost:8888/files/altair-data.json

instead of

localhost:8888/files/test/altair-data.json

for a notebook in the test directory.

The change occurred in #7022 (and #7031) where the baseURL parameter was removed from the loader.

See also #7017

Reproduce

• Create a directory test
• Inside the test directory create a new notebook with the contents

import altair as alt
import pandas as pd
alt.data_transformers.enable("json")
df = pd.DataFrame({"x": [1,2,3], "y": [1,2,3]})
alt.Chart(df).mark_line().encode(x="x", y="y")

• The chart will contain no data, a 404 error message in the terminal and the debug console.

This works in the top level directory.

Expected behavior

The chart loads the data from the directory test as per previous versions of jupyterlab, like 1.0.2.

Context

• Operating System and version: Fedora 30
• Browser and version: Firefox 68
• JupyterLab version: 1.0.6

Troubleshoot Output

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Command Line Output

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Browser Output

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[RickWalker]

We have this problem too, and it comes up in other cases - if you use a custom transformer to put all the json files from Altair in their own folder, then charts don't work. Pretty sure it's the same root cause.

[jasongrout]

I think this is fixed in #7098. If one of you can test it, that would be great!

[malramsay64]

It is working in my testing. Thank you for the fix!