Manual validation mode

[vursen]

Describe your motivation

Automatic constraint validation on every field change isn't always suitable. Consider these cases:

• Forms that should validate only on submit
• Fields with externally controlled invalid states

Describe the solution you'd like

For such cases, a manual validation mode (similar to that in Flow components) would be beneficial. It would disable the automatic validation but leave the option to trigger it programmatically by calling the validate() method, or alternatively, control the invalid state completely manually.

Here is how the API could look like:

<vaadin-text-field manual-validation />

[vursen]

LoginForm is a potential candidate to use this feature. Triggering validation only on submit could help avoid content shifts currently caused by automatic validation, see #7894 (comment)

[sissbruecker]

This might also be a proper solution for Flow components to disable client-side validation. Currently we override the _shouldSetInvalid method to always return false so that a web component never updates its invalid state. Disabling automatic validation in the web component should have the same effect and is easier to accomplish by setting an attribute or property. We need to make sure that no Flow component relies on the validated event anymore, which is still triggered with the current approach, but would not be triggered anymore when disabling automatic validation.

[web-padawan]

Prototype branch with validate() method calls replaced with _requestValidation() which checks for manualValidation property: https://github.com/vaadin/web-components/compare/proto/manual-validation

Note: if we decide to also use this in Flow like suggested above, we might also need to replace _setInvalid() method usage (and maybe get rid of it completely as it's only used in ValidateMixin and InputConstraintsMixin).