migrate: Handle single newlines in WordPress comments as line breaks

[projectgus]

WordPress renders a single newline in a comment as a
tag, but Isso renders a single newline in the comment as a single newline in the HTML. This is rendered the same as if it was a space, all text on one line.

To fix, detect single newlines when importing WordPress comments and convert to a line break in Markdown. Add a test for this also.

Example, this WordPress comment (as shown in CDATA of XML export):

First line of comment.
Second line of comment.

Renders in WordPress as:

First line of comment.
Second line of comment.

But renders in Isso after import as if it was:

First line of comment. Second line of comment.

After this commit is applied and comments re-imported, it renders as:

First line of comment.
Second line of comment.

Checklist

• All new and existing tests are passing
• (If adding features:) I have added tests to cover my changes
• (N/A) (If docs changes needed:) I have updated the documentation accordingly.
• (N/A but please tell me if you disagree) I have added an entry to CHANGES.rst because this is a user-facing change or an important bugfix
• I have written proper commit message(s)
  

[projectgus]

I haven't touched any javascript in the PR so I don't think the js integration test failures are related. I don't have access to retry the test run, though.

[ix5]

Hi @projectgus, thank you for your contribution! Especially adding a new test case is really helpful.
The e2e tests seem to have been flaky, sorry for that. Re-running (and testing the same locally), I cannot reproduce what caused that issue.

Re: Inserting a <br> element: Since some people disallow raw HTML in comments, I'd rather you do this the "native" Markdown way: Inserting two spaces at the end of the line, which will also render as a line break.

Edit: Please also remove the windows linebreak (\n\r) in the XML file.

[projectgus]

@ix5 That's funny, original version of this patch replaced with \n\n but then I second-guessed myself and changed to <br>. It's \n\n again now!

Also fixed the linebreak, nice catch. I think this was copypasta from the WordPress XML export.

Thanks for all your work on Isso, it's very useful. :)

[ix5]

Looks good, thanks for addressing the review comments.

Please also add a CHANGES entry, under "bugfixes" for the "next" version (i.e. not under 1.13.0.beta1), and if you like, add yourself to CONTRIBUTORS

[projectgus]

@ix5 Done, and rebased. Thanks!

[ix5]

Merged. Thank you for your contribution and don't hesitate to submit further PRs!