files: don't recurse into subrepos without a path or -S (issue5127)

The 'm.always()' check was needed for when a path to 'sub1' is given, and 'sub1'
contains a subrepo itself.  But that also caused the automatic recursion when no
path was given.  Instead, force -S when printing a subrepo if the subpath is an
exact match (which will unconditionally recurse once in the nested subrepo).

mercurial/cmdutil.py

@@ -2340,14 +2340,15 b' def files(ui, ctx, m, fm, fmt, subrepos)'
 
     for subpath in sorted(ctx.substate):
         def matchessubrepo(subpath):
-            return (m.always() or m.exact(subpath)
+            return (m.exact(subpath)
                     or any(f.startswith(subpath + '/') for f in m.files()))
 
         if subrepos or matchessubrepo(subpath):
             sub = ctx.sub(subpath)
             try:
                 submatch = matchmod.narrowmatcher(subpath, m)
-                if sub.printfiles(ui, submatch, fm, fmt, subrepos) == 0:
+                recurse = m.exact(subpath) or subrepos
+                if sub.printfiles(ui, submatch, fm, fmt, recurse) == 0:
                     ret = 0
             except error.LookupError:
                 ui.status(_("skipping missing subrepository: %s\n")

tests/test-subrepo-deep-nested-change.t

@@ -297,6 +297,12 b' Files sees uncommitted adds and removes '
   sub1/sub2/folder/bar (glob)
   sub1/sub2/x.txt (glob)
 
+  $ hg files
+  .hgsub
+  .hgsubstate
+  foo/bar/abc (glob)
+  main
+
   $ hg files -S -r '.^' sub1/sub2/folder
   sub1/sub2/folder/test.txt (glob)