[PATCH 1 of 6 V3] obsolete: clarify documentation for succcessorssets

[Sean Farley]

# HG changeset patch
# User Sean Farley <sean.michael.farley at gmail.com>
# Date 1389831252 21600
#      Wed Jan 15 18:14:12 2014 -0600
# Node ID 8d89a657625079b8c4e530a37d18b20de89c380e
# Parent  47d0843647d1e32f6af4482867327cec5db11a1f
obsolete: clarify documentation for succcessorssets

diff --git a/mercurial/obsolete.py b/mercurial/obsolete.py
--- a/mercurial/obsolete.py
+++ b/mercurial/obsolete.py
@@ -507,33 +507,41 @@ def foreground(repo, nodes):
 
 
 def successorssets(repo, initialnode, cache=None):
     """Return all set of successors of initial nodes
 
-    Successors set of changeset A are a group of revision that succeed A. It
-    succeed A as a consistent whole, each revision being only partial
-    replacement.  Successors set contains non-obsolete changeset only.
+    The successors set of a changeset A are a group of revisions that succeed
+    A. It succeed A as a consistent whole, each revision being only partial
+    replacement.  The successors set contains non-obsolete changeset only.
 
-    In most cases a changeset A have zero (changeset pruned) or a single
-    successors set that contains a single successor (changeset A replaced by
-    A')
+    In most cases a changeset A will have zero (e.g. the changeset pruned)
+    elements in its successors set or a successors set that contains a single
+    element (e.g. changeset A replaced by A'). Therefor, these successors sets
+    will look like [()] or [(A',)], respectively.
 
-    When changeset is split, it results successors set containing more than
-    a single element. Divergent rewriting will result in multiple successors
-    sets.
+    When changeset A is split into A' and B', however, it will result in a
+    successors set containing more than a single element, i.e. [(A',B')].
+    Divergent changesets will result in multiple successors sets, i.e. [(A',),
+    (A'')].
+
+    If a changeset A is not obsolete, then it will conceptually have no
+    successors set.  To distinguish this from a pruned changeset, the successor
+    set will only contain itself, i.e. [(A,)].
 
     They are returned as a list of tuples containing all valid successors sets.
 
-    Final successors unknown locally are considered plain prune (obsoleted
+    Finally, successors unknown locally are considered plain prune (obsoleted
     without successors).
 
-    The optional `cache` parameter is a dictionary that may contains
-    precomputed successors sets. It is meant to reuse the computation of
-    previous call to `successorssets` when multiple calls are made at the same
-    time. The cache dictionary is updated in place. The caller is responsible
-    for its live spawn. Code that makes multiple calls to `successorssets`
-    *must* use this cache mechanism or suffer terrible performances."""
+    The optional `cache` parameter is a dictionary that may contain precomputed
+    successors sets. It is meant to reuse the computation of a previous call to
+    `successorssets` when multiple calls are made at the same time. The cache
+    dictionary is updated in place. The caller is responsible for its live
+    spawn. Code that makes multiple calls to `successorssets` *must* use this
+    cache mechanism or suffer terrible performances.
+
+    """
 
     succmarkers = repo.obsstore.successors
 
     # Stack of nodes we search successors sets for
     toproceed = [initialnode]