Don't copy empty elements that were not selected on purpose as GFM

You can reproduce the bug this fixes right here in GitLab <9.3 by triple clicking "Heading 1" below, and either hitting r or copy-pasting the selection into the GFM textarea below. Tested in Chrome.

---

Heading 1

Heading 2

---

You'll see that in the inserted text, there is an extra heading without any content:

# Heading 1

## 

The reason is that when you triple-click a block-level element (in Chrome at least), it actually selects that element, as well as an empty copy of the the element that follows it. In the example above, this looks like:

<h1>Heading1</h1>

<h2></h2>

Before this change, our Copy-as-GFM logic would happily translate this <h2>[nothing]</h2> to ## [nothing], hence the result above.

With this change, we automatically trim when appropriate, and skip empty elements that need text in Markdown, so that the selection described above will result in the below, as expected:

# Heading 1

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• 1fac65ba - Don't copy empty elements that were not selected on purpose as GFM

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• 4070d58a - Don't copy empty elements that were not selected on purpose as GFM

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@mikegreiling can you please review?

assigned to @mikegreiling

This LGTM, but could we add an extra test for this?

assigned to @DouweM

resolved all discussions

assigned to @filipa

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• 850b9983 - Add spec

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@DouweM do we have tests for this? Thanks!

assigned to @DouweM

ups missed the test!

assigned to @filipa

resolved all discussions

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• 6ec1f1a7 - Remove unnecessary variable

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Thank you @DouweM

approved this merge request

merged

mentioned in commit c013d23d