Good news here, Matthias reviewed and approved my patches, so I committed them.
In the same bug report, Johannes Schmid proposed to add placeholder text to GtkCellrendererText too, and I think it makes even more sense than for entries since it’s not obvious when a treeview cell is editable. Glade has a custom implementation for the signal editor. I filed a new bug report and attached a patch.
GtkScrolledWindow: kinetic scrolling
While I was on vacation I had the opportunity to play with an Android phone for a while (thanks Roca!), I was very curious about how they solved the problem of selecting text in scrollable widgets and it turned out that they use press-and-hold. After a long press the current word is selected and two handles show up to extend the selection. I don’t like the handles, and I don’t think we need it, but the press-and-hold solution might work for us. We can simply wait after the long press to cancel the scrolling operation and propagate events to child widgets normally so that both selections and drag and drop operations will work as if kinetic scrolling mode were not enabled. I submitted a patch that uses press-and-hold to allow selections and drag and drop operations when kinetic scrolling mode is enabled in GtkScrolledWindow. However, I couldn’t use any of the solutions proposed for press-and-hold in bug #315645. As kris commented (thanks kris for your feedback in this and other bugs, by the way!), this press-and-hold use case changes the game a bit, so we’ll have to think a bit more about it.
I noticed my patch had a couple of regressions regarding GtkEntry popdown menu handling, corresponding to old bugs #169534 and #71868. Updated the patches (GtkLiveEntry and GtkTreeView) to apply on current git master and fix the regressions.