[PATCH V2] localrepo: reverse contexts in status

[Sean Farley]

# HG changeset patch
# User Sean Farley <sean.michael.farley at gmail.com>
# Date 1397684088 18000
#      Wed Apr 16 16:34:48 2014 -0500
# Node ID b96074a56e0d75b39476e37d91395505b1e01d2f
# Parent  8844e50911049ffb10c3693b6cfea7e2ea4440c7
localrepo: reverse contexts in status

This is a slight tweak to how localrepo.status calculates what files have
changed. By forcing a changectx to be first operator and anything not a
changectx to be the second operator, we can later exploit this to allow
refactoring the status operation as a method of a context object.

Furthermore, this change will speed up 'hg diff --reverse' when used with the
working directory because the code will now hit a fast path without needing to
calculate an unneeded second manifest.

diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -1521,10 +1521,28 @@ class localrepository(object):
             return mf
 
         ctx1 = self[node1]
         ctx2 = self[node2]
 
+        # This next code block is, admittedly, fragile logic that tests for
+        # reversing the contexts and wouldn't need to exist if it weren't for
+        # the fast (and common) code path of comparing the working directory
+        # with its first parent.
+        #
+        # What we're aiming for here is the ability to call:
+        #
+        # workingctx.status(parentctx)
+        #
+        # If we always built the manifest for each context and compared those,
+        # then we'd be done. But the special case of the above call means we
+        # just copy the manifest of the parent.
+        reversed = False
+        if (not isinstance(ctx1, context.changectx)
+            and isinstance(ctx2, context.changectx)):
+            reversed = True
+            ctx1, ctx2 = ctx2, ctx1
+
         working = ctx2.rev() is None
         parentworking = working and ctx1 == self['.']
         match = match or matchmod.always(self.root, self.getcwd())
         listignored, listclean, listunknown = ignored, clean, unknown
 
@@ -1579,10 +1597,13 @@ class localrepository(object):
             removed = mf1.keys()
 
         if working:
             modified = ctx2._filtersuspectsymlink(modified)
 
+        if reversed:
+            added, removed = removed, added
+
         r = modified, added, removed, deleted, unknown, ignored, clean
 
         if listsubrepos:
             for subpath, sub in scmutil.itersubrepos(ctx1, ctx2):
                 if working: