FeatureGroup do not support tooltip with permanent: true (as advertised)

[elmatou]

• I've looked at the documentation to make sure the behavior is documented and expected
• I'm sure this is a Leaflet code issue, not an issue with my own code nor with the framework I'm using (Cordova, Ionic, Angular, React…)
• I've searched through the issues to make sure it's not yet reported

Steps to reproduce
Add a featureGroup with bindToolip to the map
Add a marker to the featureGroup

Expected behavior
every Marker should own (or share in this case) a tooltip which is permanently shown.
as documented "bindPopup binds a popup to all of the layers at once (likewise with bindTooltip)"

Current behavior
no Marker is shown
no Tooltip is shown
in console I get "Error: Unable to get source layer LatLng."

Environment

• Leaflet version:
• Browser (with version):
• OS/Platform (with version):

Additional context

when removing permanent: true is removed everything works fine.

Minimal example reproducing the issue

https://next.plnkr.co/edit/S2W7zcKTkVIrFLur

• this example is as simple as possible
• this example does not rely on any third party code

[johnd0e]

every Marker should own (or share in this case) a tooltip which is permanently shown.

I do not think so. The tooltip should be single.

as documented "bindPopup binds a popup to all of the layers at once (likewise with bindTooltip)"

Documentation is not precise here, just not best wording.

[johnd0e]

in console I get "Error: Unable to get source layer LatLng."

That is because you are trying to open tooltip for empty FeatureGroup.
Addressed in #7540.

[johnd0e]

So here is correct sample:

var markerGroup = new L.FeatureGroup([new L.Marker(map.getCenter())])
  .bindTooltip('balbla Tooltip', {permanent:true})
  .addTo(map);
map
  .on('click', function(e) {
    var marker = new L.Marker(e.latlng)
      .addTo(markerGroup);
  });

This keeps single tooltip and that is intended behavior.