Horizontal ruled separator does not appear under Groups

[chigozienri]

Item('_') does not produce a visible separator when immediately underneath a Group
To replicate:

from traits.api import *
from traitsui.api import *

class SeparatorTest(HasTraits):
    view = View(
        Label('Above'),
        Item('_'),
        Label('Below'),
        Item('_'),
        Group(Label('Caverns')),
        Item('_'),
        Group(Label('Dungeons')),
        Item('_'),
        Group(Label("Extra dungeons")),
        Item('_'),
        Label('Foundations')
    )

if __name__ == "__main__":
    separator = SeparatorTest()
    separator.configure_traits()

[rahulporuri]

@nicolasap-dm points to these locations as being the potential sources of error -

traitsui/traitsui/qt4/ui_panel.py

Lines 631 to 635 in 94da89c

	# Get a panel for the Item or Group.
	if isinstance(item, Group):
	panel = _GroupPanel(item, self.ui, suppress_label=True).control
	else:
	panel = self._add_items([item])

traitsui/traitsui/item.py

Lines 91 to 93 in ca84713

	# FIXME: all the logic for the name = '', '_', ' ', '23' magic is in
	# _GroupPanel._add_items in qt/ui_panel.py, which is a very unlikely place
	# to look for it. Ideally, that logic should be in this class.

[nicolasap-dm]

(I haven't followed the whole logic there, so they may be completely misguided. On the surface, however, the snippets look relevant.)

[aaronayres35]

Looking into this a bit it seems as though the separator is there, it just gets covered by a subsequent group(?).
The last separator which is followed by a Label is shown even though it comes after a group. Also if you remove one of the separators between groups you can see that the 2 groups are shown closer together. i.e. the Item("-") is there separating the groups, but the corresponding sunken line is not visible

[aaronayres35]

Note, as a workaround I believe moving the separator inside the group "fixes" this:
ie replacing

Group(Label('Caverns')),
Item('_'),

with

Group(
    Label('Caverns'),
    Item('_'),
),

yields

[aaronayres35]

I believe the error here is really whenever a separator is the only Item in a Group (even an implicit group).
In practice this would occur is you have Item('_') directly between two groups, or did something like Group(Item('_')). In this scenario we end up setting up a QGridLayout with just the QtGui.QFrame.HLine in it. See:

traitsui/traitsui/qt4/ui_panel.py

Lines 1008 to 1043 in 20f73e8

	def _add_separator_item(self, item, columns, inner, row, col, show_labels):
	cols = columns
	# See if the layout is a grid.
	if row >= 0:
	# Move to the start of the next row if necessary.
	if col > 0:
	col = 0
	row += 1
	# Skip the row we are about to do.
	row += 1
	# Allow for the columns.
	if show_labels:
	cols *= 2
	for i in range(cols):
	line = QtGui.QFrame()
	if self.direction == QtGui.QBoxLayout.LeftToRight:
	# Add a vertical separator:
	line.setFrameShape(QtGui.QFrame.VLine)
	if row < 0:
	inner.addWidget(line)
	else:
	inner.addWidget(line, i, row)
	else:
	# Add a horizontal separator:
	line.setFrameShape(QtGui.QFrame.HLine)
	if row < 0:
	inner.addWidget(line)
	else:
	inner.addWidget(line, row, i)
	line.setFrameShadow(QtGui.QFrame.Sunken)

With nothing else in the layout I believe what is happening is the HLine effectively has no length. It is still there though, and we can see this because if we remove a separator between groups the 2 groups are shown much closer together:

So the separators are there but the line isn't visible.

Unfortunately I am not seeing an easy / clean way to fix this...
I think the best solution is to just pull the separator up into the end of the first group rather than between 2 groups.

If this workaround solves the problem, I think it is safe to close this issue