flags: read flag from dirstate/disk for workingcopyctx (issue5743)

In 491855ea9d62, various piece of code are moved from committablectx to
workingctx. The reason given is "These read from the dirstate, so they shouldn't
be used in other subclasses."

At least for `flags` this change introduce a bug, because the value flags end up being
read from `_manifest` disregarding the actual state in the working copy (ie: on
disk). When merging exec flag change with renames, this means a new files (the
local content, renamed) is properly written on disk, with the right flags, but
the flags part is later ignored when actually reading flags during merge.

It is not clear to me why the `flags` function was moved, because the code does
not actually hit the dirstate (the reason given in the changeset description).
So I am moving it back to were it comes from and we use a simpler version of
that code (that hit the dirstate everytime) in workingcopyctx. This fix the last
know bug with merging rename and executable byte changes.

Other similar bug might be lurking in 491855ea9d62, but I have not investigated
them.

Differential Revision: https://phab.mercurial-scm.org/D8534

mercurial/context.py

@@ -1458,6 +1458,18 b' class committablectx(basectx):'
     def children(self):
         return []
 
+    def flags(self, path):
+        if '_manifest' in self.__dict__:
+            try:
+                return self._manifest.flags(path)
+            except KeyError:
+                return b''
+
+        try:
+            return self._flagfunc(path)
+        except OSError:
+            return b''
+
     def ancestor(self, c2):
         """return the "best" ancestor context of self and c2"""
         return self._parents[0].ancestor(c2)  # punt on two parents for now
@@ -1594,12 +1606,6 b' class workingctx(committablectx):'
         return self._repo.dirstate.flagfunc(self._buildflagfunc)
 
     def flags(self, path):
-        if '_manifest' in self.__dict__:
-            try:
-                return self._manifest.flags(path)
-            except KeyError:
-                return b''
-
         try:
             return self._flagfunc(path)
         except OSError:

tests/test-merge-exec.t

@@ -209,6 +209,5 b' merge them (from the chmod side)'
     a
   R a
   $ [ -x z ] || echo "executable bit lost"
-  executable bit lost
 
   $ cd ..