[PATCH 2 of 2 evolve-ext] evolve: add the next() revset

[Laurent Charignon]

# HG changeset patch
# User Laurent Charignon <lcharignon at fb.com>
# Date 1433461833 25200
#      Thu Jun 04 16:50:33 2015 -0700
# Node ID 5367886c7c250c623b4dd9e2ae57f915c63bf4f3
# Parent  6910cd198dd7824af651d72b224cf66966f59788
evolve: add the next() revset

The next() revset encompasses all the revisions that will be stabilized on '.'.
If a set is given to the next revset, it means all the revisions that will
be stabilized on that set.

diff --git a/hgext/evolve.py b/hgext/evolve.py
--- a/hgext/evolve.py
+++ b/hgext/evolve.py
@@ -431,6 +431,55 @@
             ui.setconfig('alias', 'grab',
                 "! $HG rebase --dest . --rev $@ && $HG up tip")
 
+### Next revset symbol
+ at eh.revset('next')
+def revsetnext(repo, subset, x):
+    """``next()``
+    Returns the changesets that stabilize on top of a subset
+    Consider the following graph:
+
+              O d
+              |   O f
+    e O - - - X   |
+       \      |   X - - O g
+        \   c O  /
+         \    | /
+          \ b O/
+           \  |
+            \ |
+             \O a
+
+    next(e) is d
+    next(g) if f
+    next(f) is empty
+    next(head()) is d and f
+
+    Default argument is '.'
+    """
+    args = revset.getargs(x, 0, 1, 'next takes one or no arguments')
+    troubled = set()
+    troubled.update(getrevs(repo, 'unstable'))
+    if args:
+        s = revset.getset(repo, subset, x)
+    else:
+        s = set([repo['.'].rev()])
+
+    troubled.update(s)
+
+    # Iterate through the reverse dependency graph from the current node
+    # to find all the revs that will stabilize on top
+    _ , _rorder = builddependencies(repo, troubled)
+    queue = collections.deque()
+    for r in s:
+        for dependency in _rorder[r]:
+            queue.append(dependency)
+
+    nextset = set()
+    while queue:
+        r = queue.popleft()
+        queue.extend([x for x in _rorder[r] if x not in nextset])
+        nextset.add(r)
+    return subset & revset.baseset(nextset)
 
 ### Troubled revset symbol
 
diff --git a/tests/test-evolve.t b/tests/test-evolve.t
--- a/tests/test-evolve.t
+++ b/tests/test-evolve.t
@@ -1212,6 +1212,17 @@
   o  25:4c0bc042ef3b at default(draft) add j1
   |
 
+Check the next() revset:
+  $ hg log -r 'next(4a34f6744d4b)'
+  38	: add c3_ - test
+  41	: add c2prime - test
+  $ hg log -r 'next()'
+  46	: add b4_ - test
+  $ hg log -r 'next(head())'
+  38	: add c3_ - test
+  41	: add c2prime - test
+  46	: add b4_ - test
+
 Solve the full second stack and only part of the first one
   $ echo "(25::) - $(shaof c3_)"
   (25::) - 28172de7eb73578cf665e868a265caf2a2655c66