Use case: make a y out of a v and a bottom stem or a slashed o out of an o and a slash in a multiple master font. It would go something like this: add v as a component, draw a bottom stem. Once satisfied, turn the stem into a component. Glyphs helpfully does this across all masters, but you still have to go through all base glyphs and the new component and place and shuffle anchors around. This feels like a waste of time.
The question is: which anchor, because a user does not have the follow the default suggestion, or maybe, as in the case of the v/y, there is no default anchor in the first place.
I suggest, after having created the component, to select and copy the anchor you want to use, switch to the glyph of the newly created component, paste the anchor and add an underscore at the beginning. It’s relatively quick, but unfortunately you have to do it over for every master. You can script that though, if you need it often.
A # anchor would get the job done and not end up in the final font if I understand correctly. It would be an optional field in the “name the component” dialog.
What you suggest is what I’m already doing. I’m not doing it that often, but it would be a nice detail.
The hash anchor would mess with the right side bearing. I see if it can work to add an anchor to the new glyph (the tail) if the base glyph already has some.
Which anchor would you suggest then, if it’s sole purpose is glyph building and therefore should not clutter the final font?
That is not necessarily a problem; you can reuse an existing mark attachment anchor for component building. Or are you thinking about a specific case?
I remember reading that special case anchors like # and e.g. emoji-prefixed ones do not turn up in the generated OpenType code. I just like to keep things clean.
I added that if the base component already has normal attachment anchors (top, bottom) it will put a corresponding anchor in the new glyph.
Sounds good 