context: use `dirstate.set_tracked` in `context.add`

This is the new shiny API.

Differential Revision: https://phab.mercurial-scm.org/D11014

mercurial/context.py

@@ -1701,12 +1701,8 b' class workingctx(committablectx):'
                         % uipath(f)
                     )
                     rejected.append(f)
-                elif ds[f] in b'amn':
+                elif not ds.set_tracked(f):
                     ui.warn(_(b"%s already tracked!\n") % uipath(f))
-                elif ds[f] == b'r':
-                    ds.normallookup(f)
-                else:
-                    ds.add(f)
             return rejected
 
     def forget(self, files, prefix=b""):

mercurial/dirstate.py

@@ -85,7 +85,7 b' def requires_parents_change(func):'
 
 def requires_no_parents_change(func):
     def wrap(self, *args, **kwargs):
-        if not self.pendingparentchange():
+        if self.pendingparentchange():
             msg = 'calling `%s` inside of a parentchange context'
             msg %= func.__name__
             raise error.ProgrammingError(msg)