context: add specialized way of getting copy source file only

I'm working on support for storing copy metadata in the changeset
instead of the filelog. I don't intend to include the file nodeid
there, but most callers don't need that anyway. This patch introduces
a method similar to ctx.renamed(), but the new method returns only the
source filename, not the nodeid. Subsequent patches will move callers
over to this new method.

Differential Revision: https://phab.mercurial-scm.org/D6008

hgext/remotefilelog/remotefilectx.py

@@ -136,6 +136,10 b' class remotefilectx(context.filectx):'
                 pass
         return renamed
 
+    def copysource(self):
+        copy = self.renamed()
+        return copy and copy[0]
+
     def ancestormap(self):
         if not self._ancestormap:
             self._ancestormap = self.filelog().ancestormap(self._filenode)

mercurial/context.py

@@ -691,6 +691,8 b' class basefilectx(object):'
         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 b' class workingfilectx(committablefilectx)'
         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 b' class overlayworkingfilectx(committablef'
             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)