[PATCH 2 of 3 stable V3] ancestor.deepest: decrement ninteresting correctly (issue3984)

[Siddharth Agarwal]

# HG changeset patch
# User Wei, Elson <elson.wei at gmail.com>
# Date 1374744953 -28800
#      Thu Jul 25 17:35:53 2013 +0800
# Branch stable
# Node ID 9324b72460bba1e668851e57928ff7b7cc75aa06
# Parent  acd8063547ca3cb47f65140be7930b60fefd9cdc
ancestor.deepest: decrement ninteresting correctly (issue3984)

The invariant this code tries to hold is that ninteresting is the number of
non-zero elements in the interesting array. interesting[nsp] is incremented at
the same time as interesting[sp] is decremented. So if interesting[nsp] was
previously 0, ninteresting shouldn't be decremented.

diff --git a/mercurial/parsers.c b/mercurial/parsers.c
--- a/mercurial/parsers.c
+++ b/mercurial/parsers.c
@@ -1362,10 +1362,10 @@
 				if (nsp == sp)
 					continue;
 				seen[p] = nsp;
+				interesting[sp] -= 1;
+				if (interesting[sp] == 0 && interesting[nsp] > 0)
+					ninteresting -= 1;
 				interesting[nsp] += 1;
-				interesting[sp] -= 1;
-				if (interesting[sp] == 0)
-					ninteresting -= 1;
 			}
 		}
 		interesting[sv] -= 1;