diff -r 3461814417f3 -r 0bd56c291359 mercurial/hgweb/webcommands.py
--- a/mercurial/hgweb/webcommands.py	Mon Jan 21 15:29:14 2019 +0000
+++ b/mercurial/hgweb/webcommands.py	Fri Jan 25 23:36:23 2019 -0800
@@ -884,7 +884,7 @@
             leftlines = filelines(pfctx)
     else:
         rightlines = ()
-        pfctx = ctx.parents()[0][path]
+        pfctx = ctx.p1()[path]
         leftlines = filelines(pfctx)
 
     comparison = webutil.compare(context, leftlines, rightlines)