With the `<amp-carousel>` 0.2 script, the right arrow sometimes shows on the last slide

[kienstra]

What's the issue?

In an <amp-carousel> using the 0.2 script:

<script async custom-element="amp-carousel" src="https://cdn.ampproject.org/v0/amp-carousel-0.2.js"></script>

...sometimes a right arrow appears even when there's only 1 slide, or if the last slide is showing. This issue doesn't appear with the 0.1 script.

Maybe this isn't an issue with AMP HTML, and there's some styling we could apply to prevent this. I first saw this in the AMP Plugin for WordPress: ampproject/amp-wp#3115

How do we reproduce the issue?

Here's a CodePen of it. On changing amp-carousel-0.2.js back to amp-carousel-0.1.js in that CodePen, the issue doesn't appear anymore.

Steps to reproduce in WordPress

1. Checkout this PR's branch, and activate Twenty Nineteen
2. Create a new post
3. Add a Gallery block
4. Add only one image to it, like this
5. Select 'Display as carousel'
6. Click 'Preview,' and go to the AMP URL
7. Expected: Because there's only 1 image in the carousel, there shouldn't be a right arrow
8. Actual: There's a right arrow, but clicking it doesn't do anything:

9. Create another Gallery block, but with at least 2 images
10. Select 'Display as carousel'
11. Click 'Preview,' and go to the AMP URL
12. Expected: When the last slide in the carousel displays, the right arrow shouldn't be visible
13. Actual: It's still visible:

This isn't a common issue, and I didn't see it with most Core themes. Maybe there's some styling that Twenty Nineteen has that's associated with this issue.

What browsers are affected?

Chrome Desktop Version 78.0.3904.87 (Official Build) (64-bit)

This issue doesn't seem to exist on Firefox or Safari

Which AMP version is affected?

1911062056110

I first noticed this issue yesterday.

[westonruter]

@kienstra I'm not seeing the same thing. If I open that CodePen, for the first carousel, I see no arrow:

And in the second I see no next arrow:

[kienstra]

@kienstra I'm not seeing the same thing. If I open that CodePen, for the first carousel, I see no arrow:

OK, thanks for testing this. Maybe it's my version of Chrome.

[kienstra]

Since you can't reproduce this with that CodePen, maybe this issue is unique to my browser. I'm closing this.

[schlessera]

I can see the same issue as @kienstra in the Codepen he posted. However, it seems to randomly appear and disappear based on resize/repaints...

Google Chrome:

This issue should be reopened.

[kienstra]

@schlessera, thanks for testing this issue and posting the .gif with details.