Required SelectDateWidget renders invalid HTML

[Kevin Brown]

When you render a SelectDateWidget for a field marked as required, I noticed it produced output that does not meet the HTML standard per ​https://www.w3.org/TR/html5/sec-forms.html#placeholder-label-option. This was called out in the 3.0 release notes so I checked out #29056 and determined that was likely the cause.

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The specific issue is that a SelectDateWidget, when specified as a required field, will generate a placeholder attribute on each of the <select> boxes which it generates. The placeholder attribute is not valid for a <select> box and instead a "placeholder" option must be specified as an <option> with an empty value (value="") with the text containing the placeholder to display.

From a Django forms perspective, this would be equivalent to setting the empty_label for the SelectDateWidget to (_('Year'), _('Month'), _('Day')), which would generate each of the placeholder label options for each of the corresponding <select> boxes used by the widget.

It's also important to note that the HTML generated for the SelectDateWidget in previous versions of Django was valid per the HTML standard. They did not contain a placeholder label option, but because they were not a <select multiple> they always contained an option with a selectedness set to true (usually the first option). This meant that the required attribute generated for them was useless, since it would never not have a value or be empty, but it did mean it was still valid HTML.

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Here's some relevant parts of the standard when it comes to required select boxes.

If a select element has a required attribute specified, does not have a multiple attribute specified, and has a display size of 1; and if the value of the first option element in the select element's list of options (if any) is the empty string, and that option element's parent node is the select element (and not an optgroup element), then that option is the select element's placeholder label option.

If a select element has a required attribute specified, does not have a multiple attribute specified, and has a display size of 1, then the select element must have a placeholder label option.

Constraint validation: If the element has its required attribute specified, and either none of the option elements in the select element's list of options have their selectedness set to true, or the only option element in the select element's list of options with its selectedness set to true is the placeholder label option, then the element is suffering from being missing.

You can also find the list of accepted attributes for a <select> at ​https://html.spec.whatwg.org/multipage/form-elements.html#the-select-element and ​https://developer.mozilla.org/en-US/docs/Web/HTML/Element/select#Attributes. Note that neither of those pages specify that a <select> element may have a placeholder attribute.

[Baptiste Mispelon]

Hi,

Thanks for the report.

I've reopened the original ticket and updated its severity to "release blocker" so I will close this one as a duplicate and the discussion can continue over there.

[Carlton Gibson]

This isn't quite a duplicate: a regression was introduced in #29056. We'll track resolving that here.

I'm reviewing this now, but will Accept and mark as RB, since Baptiste is on the case already.

​PR

[Carlton Gibson]

Update: good analysis Kevin, thank you, exactly on mark. To the PR...

[Carlton Gibson]

As per the PR, I'm minded to revert f038214d917c982613f5a15db8dfe325b1f7479b for 3.0 and allow a new ticket to add required handling as a New Feature.

[Mariusz Felisiak <felisiak.mariusz@…>]

In ee4a1905:

Fixed #31012 -- Reverted "Fixed #29056 -- Fixed HTML5 validation of required SelectDateWidget."

This reverts commit f038214d917c982613f5a15db8dfe325b1f7479b.

The initial issue was incorrect. Django 2.2, and before, did not
generate invalid HTML as reported. With f03821 in place invalid HTML
was generated.

Thanks to Kevin Brown for follow-up report and investigation.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 947f8e3:

[3.0.x] Fixed #31012 -- Reverted "Fixed #29056 -- Fixed HTML5 validation of required SelectDateWidget."

This reverts commit f038214d917c982613f5a15db8dfe325b1f7479b.

The initial issue was incorrect. Django 2.2, and before, did not
generate invalid HTML as reported. With f03821 in place invalid HTML
was generated.

Thanks to Kevin Brown for follow-up report and investigation.
Backport of ee4a19053a32d41cdd79e087b1968980804ce658 from master