[ComboBox] Validation does not check pattern

[vursen]

Description

Although setPattern is available in ComboBox, it only sets the related attribute and doesn't affect validation. This contrasts with the web component where the pattern is actually checked during validation. Without validation, the purpose of the pattern is unclear.

Expected outcome

ComboBox should invalidate if the custom value doesn't match the pattern, same as it works in the web component.

Minimal reproducible example

ComboBox<String> comboBox = new ComboBox<>();
comboBox.setPattern("^\\d+$");
comboBox.setAllowCustomValue(true);

Environment

Vaadin version(s): 24.5 and earlier OS: Mac OS

Browsers

No response

[vursen]

After discussing this issue, we reached a consensus that pattern makes too little sense for both ComboBox and MultiSelectComboBox. While these fields resemble classic text fields, they are different because their values are typically beans rather than strings. This means that pattern can only validate the string representation of these values, which seems to be rather niche and not worth being supported out of the box. Therefore, our decision is to deprecate the pattern constraint in these components in both their versions: WC and Flow.

[web-padawan]

Based on the git history, the pattern property was initially just propagated to the underlying vaadin-text-field since https://github.com/vaadin/vaadin-combo-box/pull/557. Before switching to vaadin-text-field, the iron-input and allowedPattern was used (which worked like our allowedCharPattern, which is now supported by all input controls including vaadin-combo-box).

BTW the vaadin-multi-select-combo-box doesn't even use pattern property and I think it doesn't need it.