MOBI Output: Fix underline and strikethrough properties declared on parents not being rendered on child tags. Fixes #894245 (Private bug)

src/calibre/ebooks/mobi/mobiml.py

@@ -376,8 +376,8 @@ class MobiMLizer(object):
         istate.preserve = (style['white-space'] in ('pre', 'pre-wrap'))
         istate.bgcolor  = style['background-color']
         istate.fgcolor  = style['color']
-        istate.strikethrough = style['text-decoration'] == 'line-through'
-        istate.underline = style['text-decoration'] == 'underline'
+        istate.strikethrough = style.effective_text_decoration == 'line-through'
+        istate.underline = style.effective_text_decoration == 'underline'
         ff = style['font-family'].lower() if style['font-family'] else ''
         if 'monospace' in ff or 'courier' in ff or ff.endswith(' mono'):
             istate.family = 'monospace'

src/calibre/ebooks/oeb/stylizer.py

@@ -714,6 +714,26 @@ class Style(object):
             self._lineHeight = result
         return self._lineHeight
 
+    @property
+    def effective_text_decoration(self):
+        '''
+        Browsers do this creepy thing with text-decoration where even though the
+        property is not inherited, it looks like it is because containing
+        blocks apply it. The actual algorithm is utterly ridiculous, see
+        http://reference.sitepoint.com/css/text-decoration
+        This matters for MOBI output, where text-decoration is mapped to <u>
+        and <st> tags. Trying to implement the actual algorithm is too much
+        work, so we just use a simple fake that should cover most cases.
+        '''
+        css = self._style.get('text-decoration', None)
+        pcss = None
+        parent = self._get_parent()
+        if parent is not None:
+            pcss = parent._style.get('text-decoration', None)
+        if css in ('none', None) and pcss not in (None, 'none'):
+            return pcss
+        return css
+
     @property
     def marginTop(self):
         return self._unit_convert(