Fix forms input placeholder displaying when its value is "0"

[tellthemachines]

Fixes #41725

Proposed changes:

• If an input placeholder has any value at all in it, it should display. This changes the check from empty() to explicitly check if the string value is empty instead.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

• Add a contact form to a post or page.
• Set the placeholder on one of the inputs to "0".
• Save and check that the value "0" displays on the front end.

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack), and enable the fix/zero-placeholder branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack fix/zero-placeholder

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

• ✅ Include a description of your PR changes.
  
• ✅ Add a "[Status]" label (In Progress, Needs Review, ...).
  
• ✅ Add a "[Type]" label (Bug, Enhancement, Janitorial, Task).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation 🤖

---

Follow this PR Review Process:

1. Ensure all required checks appearing at the bottom of this PR are passing.
2. Make sure to test your changes on all platforms that it applies to. You're responsible for the quality of the code you ship.
3. You can use GitHub's Reviewers functionality to request a review.
4. When it's reviewed and merged, you will be pinged in Slack to deploy the changes to WordPress.com simple once the build is done.

If you have questions about anything, reach out in #jetpack-developers for guidance!

[jp-launch-control]

Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

Full summary · PHP report · JS report

[andrewserong]

Good catch, this is testing well for me! Supports a 0 placeholder now (tested with the Animated style of the form):

Just left a comment about potentially checking for null values just in case, but in practice I wasn't able to run into any issues with the current state of things.

LGTM!

[andrewserong]

Tiny nit: I'm not very familiar with this code, but from the looks of it, it might be technically possible for $placeholder to be null.

I.e. it looks like the placeholder is set here, which gets retrieved from the shortcode via get_attribute, which falls back to null.

In that case, would it be safer to check for ! isset( $placeholder ) || '' === $placeholder? Though in practice, I haven't been able to break this in manual testing, so I might very well be overthinking it!

[tellthemachines]

Oh good point, maybe it would be safer to do that. What I don't get is the reason for this condition, as it seems we're just adding a space to $placeholder if it's empty 🤔

[tellthemachines]

Just confirmed and it's super weird that adding styles to the form to trigger that condition means any field without a placeholder suddenly acquires placeholder=" ":

This feels like a mistake. CC @simison in case you have any context on this?