mercurial/context.py

--- a/mercurial/context.py	Thu Feb 21 21:27:42 2019 -0800
+++ b/mercurial/context.py	Sun Mar 25 21:32:16 2018 -0700
@@ -691,6 +691,8 @@
         return self._changectx
     def renamed(self):
         return self._copied
+    def copysource(self):
+        return self._copied and self._copied[0]
     def repo(self):
         return self._repo
     def size(self):
@@ -1703,6 +1705,8 @@
         if not rp:
             return None
         return rp, self._changectx._parents[0]._manifest.get(rp, nullid)
+    def copysource(self):
+        return self._repo.dirstate.copied(self._path)
 
     def size(self):
         return self._repo.wvfs.lstat(self._path).st_size
@@ -2148,6 +2152,9 @@
             return None
         return path, self._changectx._parents[0]._manifest.get(path, nullid)
 
+    def copysource(self):
+        return self._parent.copydata(self._path)
+
     def size(self):
         return self._parent.size(self._path)