Preview and Diff functions fail with data-include

[jandrieu]

Description of problem

When using data-include, it fails to render in Github previews and diffs.

URL to affected spec or repo:

w3c/vc-use-cases#145

What happened (e.g., it crashed)?:

The rendered html shows errors because the relative URL of the include points to files that don't exist.

Expected behavior (e.g., it shouldn't crash):

The included files should render

Optional, steps to reproduce:

1. Add a data-include attribute that includes a local file, merge it in.
2. Verify that the merge is in the current rendering (github.io)
3. Make a new branch, somewhere.
4. Change a file. Commit that to the new branch
5. Make a PR to merge new branch
6. Click on the preview or diff link in the PR review

You'll note that the data-includes do not get rendered in the preview.

The underlying cause is that the relative URL takes on the base of the preview, which isn't the branch.

I don't know how the preview and diff functions are configured, but it seems that code could set the base using a URL that points to the branch that is being merged in.

Are those preview and diff functions under the ReSpec umbrella or something else?

[sidvishnoi]

@jandrieu This belongs to tobie/pr-preview.

[jandrieu]

For my own sanity, here's the issue over there. tobie/pr-preview#144