I have an internal Schriftlabor tool that does exactly that, look for overlaps. It is reliable but slow. Georg gave me good input for a better algorithm, and I have been wanting to rewrite it for ages. But I can send you an e-mail with it if you like.
nope.
In console I see
24/04/18 17:43:55,804 Glyphs[60840]: Missing Category Filter: CATEGORIES
24/04/18 17:43:56,166 Glyphs[60840]: Missing Category Filter: All
Traceback (most recent call last):
File “GlyphsApp/GlyphsApp/plugins.py”, line 1137, in drawForegroundForLayer_options_
File “/Users/xxxxx/Library/Application Support/Glyphs/Repositories/Stem Thickness/StemThickness.glyphsReporter/Contents/Resources/StemThickness.py”, line 96, in foreground
closestData = self.calcClosestInfo(layer, crossHairCenter)
File “/Users/xxxxx/Library/Application Support/Glyphs/Repositories/Stem Thickness/StemThickness.glyphsReporter/Contents/Resources/StemThickness.py”, line 263, in calcClosestInfo
n = math.floor(closestPathTime)
TypeError: a float is required