Customisable select panel height

Please describe the feature you would like to request.

Configuration of the panel height for MatSelect.

What is the use-case or motivation for this proposal?

• display more select options to the user if screen estate allows it
• fix repositioning of clicked option when the panel is opened with select:multiple

Is there anything else we should know?

This is part feature, part fix as my main use case was the following:

• use a select with multiple choice
• display more options by overriding the panel max-height style as suggested in #11780

This suggestion works, but adds a weird repositioning of the selected option if it is below the hardcoded 256px limit. It is reproducible with all versions below angular-material 7.3.7 (and including master).

Reproductible test case: https://stackblitz.com/edit/angular-select-panel video: https://streamable.com/g0z7k

This snippet is based on the multiple select example from the documentation. I simply added a class to increase the height of the select panel. If you select anything below the Leek option, the scrollbar is moved to make the option “visible” in the panel. The option is obviously visible to us, but as the height of the panel is hardcoded at 256px, it is considered out of it by the computation of MatSelect component.

I initially only wanted to fix the issue I just described, but after reviewing the component’s code, I thought it would be cleaner to freely configure the panel’s height. Depending on screen space availability, people can decide how big they want the panel to be. Additionally it can also be dynamically set if one wants to support multiple screen sizes.

This would fix:

• the issue described above
• #11780
• #15192

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