subrepo: adjust subrepo prefix before calling subrepo.add() (API)

Differential Revision: https://phab.mercurial-scm.org/D5884

mercurial/cmdutil.py

@@ -2059,10 +2059,11 b' def add(ui, repo, match, prefix, explici'
         sub = wctx.sub(subpath)
         try:
             submatch = matchmod.subdirmatcher(subpath, match)
+            subprefix = repo.wvfs.reljoin(prefix, subpath)
             if opts.get(r'subrepos'):
-                bad.extend(sub.add(ui, submatch, prefix, False, **opts))
+                bad.extend(sub.add(ui, submatch, subprefix, False, **opts))
             else:
-                bad.extend(sub.add(ui, submatch, prefix, True, **opts))
+                bad.extend(sub.add(ui, submatch, subprefix, True, **opts))
         except error.LookupError:
             ui.status(_("skipping missing subrepository: %s\n")
                            % join(subpath))

mercurial/subrepo.py

@@ -518,9 +518,7 b' class hgsubrepo(abstractsubrepo):'
 
     @annotatesubrepoerror
     def add(self, ui, match, prefix, explicitonly, **opts):
-        return cmdutil.add(ui, self._repo, match,
-                           self.wvfs.reljoin(prefix, self._path),
-                           explicitonly, **opts)
+        return cmdutil.add(ui, self._repo, match, prefix, explicitonly, **opts)
 
     @annotatesubrepoerror
     def addremove(self, m, prefix, opts):