pager: replace fout and ferr of all ui objects

Summary:
The `ui` object is a bit messy - there are repo specific ui, and non-repo ui,
and ui can be copied around.

This diff changes `fout` and `ferr` to an indirect type that can be mutated
globally so the streampager can affect the `fout` and `ferr` of all related `ui`
objects instead of just one single `ui`.

Reviewed By: DurhamG

Differential Revision: D20903568

fbshipit-source-id: b2f139b91a39c20c22261e03ce50f3cc59074291

eden/scm/edenscm/mercurial/dispatch.py

@@ -73,6 +73,13 @@ class request(object):
         self.repo = repo
 
         # input/output/error streams
+        if fin and not isinstance(fin, util.refcell):
+            fin = util.refcell(fin)
+        if fout and not isinstance(fout, util.refcell):
+            fout = util.refcell(fout)
+        if ferr and not isinstance(ferr, util.refcell):
+            ferr = util.refcell(ferr)
+
         self.fin = fin
         self.fout = fout
         self.ferr = ferr

eden/scm/edenscm/mercurial/ui.py

@@ -204,9 +204,9 @@ class ui(object):
         else:
             self._uiconfig = uiconfig.uiconfig()
 
-            self.fout = util.stdout
-            self.ferr = util.stderr
-            self.fin = util.stdin
+            self.fout = util.refcell(util.stdout)
+            self.ferr = util.refcell(util.stderr)
+            self.fin = util.refcell(util.stdin)
             self.pageractive = False
             self._disablepager = False
             self._tweaked = False
@@ -825,8 +825,6 @@ class ui(object):
 
     def _runinternalstreampager(self):
         """Start the builtin streampager"""
-        origfout = self.fout
-        origferr = self.ferr
         origencoding = encoding.outputencoding
         self.flush()
 
@@ -850,15 +848,17 @@ class ui(object):
             def close(self):
                 pass
 
-        self.fout = stream(pager.write)
-        self.ferr = stream(pager.write_err)
+        assert isinstance(self.fout, util.refcell)
+        assert isinstance(self.ferr, util.refcell)
+        origfout = self.fout.swap(stream(pager.write))
+        origferr = self.ferr.swap(stream(pager.write_err))
 
         @self.atexit
         def waitpager():
             with self.timeblockedsection("pager"):
                 pager.close()
-            self.fout = origfout
-            self.ferr = origferr
+            self.fout.swap(origfout)
+            self.ferr.swap(origferr)
             encoding.outputencoding = origencoding
 
         self.pageractive = True

eden/scm/edenscm/mercurial/util.py

@@ -645,6 +645,34 @@ class transactional(pycompat.ABC):
             self.release()
 
 
+class refcell(object):
+    """Similar to Rust's Rc<RefCell>. Shared *mutable* reference.
+
+    This is useful when object mutation needs to affect shared copies.
+
+    >>> a = refcell("abc")
+    >>> b = a
+    >>> a.swap("defg")
+    'abc'
+    >>> b.upper()
+    'DEFG'
+    """
+
+    def __init__(self, obj):
+        self._obj = obj
+
+    def __getattr__(self, name):
+        return getattr(self._obj, name)
+
+    def __iter__(self):
+        return iter(self._obj)
+
+    def swap(self, obj):
+        origobj = self._obj
+        self._obj = obj
+        return origobj
+
+
 @contextlib.contextmanager
 def acceptintervention(tr=None):
     """A context manager that closes the transaction on InterventionRequired

eden/scm/tests/test-dirstate-backup.t

@@ -1,9 +1,5 @@
 #chg-compatible
 
-#chg-compatible
-
-#chg-compatible
-
 #testcases v0 v1 v2
 
 #if v0