[Sort] Sort icon should appear on hover

[andrewseguin]

The spec says that the sort icons should appear when the header is hovered to indicate that the header is sortable.

[donroyco]

@andrewseguin How would you do this on mobile devices?

[andrewseguin]

Perhaps similar to tooltip, longpress can expose the icon without triggering the sort.

[willshowell]

I'd like to piggy back on this to suggest similar behavior on focus. Currently there is no visual indication that an action can be taken when tabbing through the mat-sort-header-buttons.

[Misiu]

@andrewseguin does this mean that user won't see what column is sorted when he enters site? The only way to know what column is sorted will be to hover over header? Will there be an option to show sort icons by default and not when header is hovered?

[willshowell]

@Misiu I believe the change will do the following

1. If a column is not yet sorted, hovering/focusing/longpressing the header will show the sort icon
2. If a column is sorted, the icon will show until the column becomes unsorted (existing behavior)

[Misiu]

I got confused because I thought that sort icons will only show when hovering.
@willshowell thanks for clarification.