New text-filter mechanism to prevent interference of multiple filters

By now, each text filter cuts out the out-filtered parts, so all following
filters operate on the already modified text. This leads to mistakes.

The new mechanism first stores, which parts have to be cut out for
each filter, merges these ranges and in the end actualy cuts the text.

https://bugzilla.gnome.org/show_bug.cgi?id=758478

meld/filediff.py

@@ -762,41 +762,29 @@ class FileDiff(melddoc.MeldDoc, gnomeglade.Component):
                                                 None, True)
             self.queue_draw()
 
-    def _filter_text(self, txt, buf, start_iter, end_iter):
+    def _filter_text(self, txt, buf, txt_start_iter, txt_end_iter):
         dimmed_tag = buf.get_tag_table().lookup("dimmed")
-        buf.remove_tag(dimmed_tag, start_iter, end_iter)
+        buf.remove_tag(dimmed_tag, txt_start_iter, txt_end_iter)
 
-        def killit(m):
-
-            def get_match_iters(match, match_index=0):
-                start = start_iter.copy()
-                end = start_iter.copy()
-                start.forward_chars(match.start(match_index))
-                end.forward_chars(match.end(match_index))
-                return start, end
-
-            assert m.group().count("\n") == 0
-            if len(m.groups()):
-                s = m.group()
-                for i in reversed(range(1, len(m.groups())+1)):
-                    g = m.group(i)
-                    if g:
-                        start, end = get_match_iters(m, i)
-                        buf.apply_tag(dimmed_tag, start, end)
+        try:
+            filter_ranges = []
 
-                        s = s[:m.start(i)-m.start()]+s[m.end(i)-m.start():]
+            for filt in self.text_filters:
+                if filt.active:
+                    for match in filt.filter.finditer(txt):
+                        filter_ranges.append(match.span())
 
-                return s
-            else:
-                start, end = get_match_iters(m)
-                buf.apply_tag(dimmed_tag, start, end)
+            filter_ranges = misc.merge_intervals(filter_ranges)
 
-                return ""
+            for (start, end) in reversed(filter_ranges):
+                assert txt[start:end].count("\n") == 0
+                txt = txt[:start] + txt[end:]
+                start_iter = txt_start_iter.copy()
+                start_iter.forward_chars(start)
+                end_iter = txt_start_iter.copy()
+                end_iter.forward_chars(end)
+                buf.apply_tag(dimmed_tag, start_iter, end_iter)
 
-        try:
-            for filt in self.text_filters:
-                if filt.active:
-                    txt = filt.filter.sub(killit, txt)
         except AssertionError:
             if not self.warned_bad_comparison:
                 misc.error_dialog(
@@ -807,6 +795,7 @@ class FileDiff(melddoc.MeldDoc, gnomeglade.Component):
                         u"not be accurate.") % filt.label,
                 )
                 self.warned_bad_comparison = True
+
         return txt
 
     def after_text_insert_text(self, buf, it, newtext, textlen):