[Link module] Validation for title but no link, when title optional

Hi!
This looks really good improvement and works similarly to the opposite validation (title required), but I think the error should be set on the Url field, not Title.

Testing details

• Pulled latest core 8.5.x from git and installed it with standard profile.
• Added the link field to the basic page content type and configured "Allow link text" as optional, field itself optional, "Allowed link types" internal and external.
• Created new page, filled title field and url field empty, page is saved and title field is lost.
• Applied the patch, tried again and the validation kicks in, url field was set required, title field highlighted in red.

In my opinion, the Title field should be normal and Url field highlighted with error.

@mark_fullmer, Your patch works for me as mentioned in "Proposed Solution"
I Checked your patch by following steps:
> Add Link Field to Article Content Type.
> Add Link Title text & leaving Blank the URL field.
> It fires the Validation to add the value in URL
> Without adding both values, It didn't fire any validation.
> Also, It saves the details while editing the content.

Thank you for working on this! Glad to see test coverage for the fix, and thanks for the screenshot which is very helpful.

Shouldn't the validation be flagging the URL field, since that's where the error is? Or both of them?

For the message, I'd suggest:

The @url field is required when the @text field is specified.

Also I'm not sure the URL field should be marked required during this validation step. If the field itself is not required, both could be left blank, but this validation might confuse the user into thinking they must enter something when it's also an option to leave both fields blank.

Thanks!

I can confirm that patch in #10 works as described. Code looks solid. Looking at the latest build in Jenkins everything passed, including the LinkFieldTest class (16:05:27 Drupal\Tests\link\Functional\LinkFieldTest 6 passes).

I feel confident enough to consider it reviewed.

Thanks!

+++ b/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php
@@ -242,6 +253,12 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
 
+    // If a title field is optional, ensure that if it is entered, there is
+    // a corresponding URI entered (instead of having save silently fail).

I had to read this comment a couple of times, would this be clearer:

"Ensure that a URI is always entered when an optional title field is submitted."

Updated patch to incorporate catch's comments.

I have also added this same functionality when the title field is required. If you just enter a title and try and submit the form will still submit. So this functionality really shouldn't only apply to optional title fields.

Tested #18 this time with both an optional and required title text, both cases were behaving as described. Moving to RTBC.

Thanks lreynaga for testing the patch!

Committed/pushed to 8.6.x and cherry-picked to 8.5.x. Thanks!