[PATCH 1 of 2] reachableroots: bail if integer object cannot be allocated

[Yuya Nishihara]

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1439523116 -32400
#      Fri Aug 14 12:31:56 2015 +0900
# Node ID 949f27368952a03365a84ec81d1a6aefe4e8319a
# Parent  0b57b77f9b3ed5c1cc24ce95173c4f7e824df13f
reachableroots: bail if integer object cannot be allocated

This patch also replaces Py_XDECREF() by Py_DECREF() because we known "val"
and "p" are not NULL.

BTW, we can eliminate some of these allocation and error handling of int objects
if the internal "seen" array has more information. For example,

  enum { SEEN = 1, ROOT = 2, REACHABLE = 4 };
  /* ... build ROOT mask from roots argument ... */
  if (seen[revnum + 1] & ROOT) {  /* instead of PySet_Contains(roots, val) */

>From my quick hack, it is 2x faster.

diff --git a/mercurial/parsers.c b/mercurial/parsers.c
--- a/mercurial/parsers.c
+++ b/mercurial/parsers.c
@@ -1185,14 +1185,16 @@ static PyObject *reachableroots(indexObj
 		/* Add the node to reachable if it is a root*/
 		revnum = tovisit[k++];
 		val = PyInt_FromLong(revnum);
+		if (val == NULL)
+			goto bail;
 		if (PySet_Contains(roots, val) == 1) {
 			PySet_Add(reachable, val);
 			if (includepath == 0) {
-				Py_XDECREF(val);
+				Py_DECREF(val);
 				continue;
 			}
 		}
-		Py_XDECREF(val);
+		Py_DECREF(val);
 
 		/* Add its parents to the list of nodes to visit */
 		if (revnum != -1) {
@@ -1223,9 +1225,15 @@ static PyObject *reachableroots(indexObj
 					goto bail;
 				for (k = 0; k < 2; k++) {
 					PyObject *p = PyInt_FromLong(parents[k]);
-					if (PySet_Contains(reachable, p) == 1)
-						PySet_Add(reachable, PyInt_FromLong(i));
-					Py_XDECREF(p);
+					if (p == NULL)
+						goto bail;
+					if (PySet_Contains(reachable, p) == 1) {
+						val = PyInt_FromLong(i);
+						if (val == NULL)
+							goto bail;
+						PySet_Add(reachable, val);
+					}
+					Py_DECREF(p);
 				}
 			}
 		}