A possible UI is to split the search key on the current filetype’s scope separator (like . for Python, :: for C++), then match the last part against tmtag->name and the preceding parts against tmtag->scope.
So it would be neccessary to type `Classname::length` to find it?
Thats possibly useful, but just manually duplicates what `right click->goto symbol definition` does. Ok it helps if I don't have a use of `length` in front of me, but then why would I be searching for it?
For the Treebrowser, its a plugin, so I don't care what you do, I think the idea of having a second rate filemanager embedded in an IDE is silly and don't use it. You should open a linked issue on geany-plugins for discussions about it, rather than here.
Attempts to keep the Glib dependency low will probably cease (for a while) when GTK2 is dropped, but thats still far into the future.