Fix a DateTime leak

D860568 fixed a double free, but introduced a leak. If no
timezone is specified in the input string, timelib_fill_holes
would clone the one from m_time. Since we unconditionally cloned
*that* into m_tz, the clone from timelib_fill_holes was leaked.

The contract seems to be that m_time doesn't own it's tz_info, but
that it should be owned by a smart pointer somewhere. So we can tell
timelib_fill_holes *not* to clone the tz_info from its second parameter,
and at the same time optimize for the usual case where that timezone
is already the current timezone.

hphp/runtime/base/time/datetime.cpp

@@ -764,19 +764,21 @@ bool DateTime::fromString(CStrRef input, SmartObject<TimeZone> tz,
   }
 
   // needed if any date part is missing
-  timelib_fill_holes(t, m_time.get(), 0);
+  timelib_fill_holes(t, m_time.get(), TIMELIB_NO_CLONE);
   timelib_update_ts(t, m_tz->get());
 
   int error2;
   m_timestamp = timelib_date_to_int(t, &error2);
   if (error1 || error2) {
-    timelib_tzinfo_dtor(t->tz_info);
+    // Don't free t->tz_info, it belongs to GetTimeZoneInfo
     timelib_time_dtor(t);
     return false;
   }
 
   m_time = TimePtr(t, time_deleter());
-  m_tz = NEWOBJ(TimeZone)(timelib_tzinfo_clone(t->tz_info));
+  if (t->tz_info != m_tz->get()) {
+    m_tz = NEWOBJ(TimeZone)(timelib_tzinfo_clone(t->tz_info));
+  }
   return true;
 }
 

hphp/test/slow/ext_datetime/strtotime_leak.php

@@ -0,0 +1,31 @@
+<?php ;
+
+error_reporting(0);
+
+function test() {
+  for ($i = 0; $i < 10000; $i++) {
+    strtotime("10 September 2000");
+    strtotime("10 September 2000 UTC");
+    strtotime("null");
+  }
+}
+
+function main() {
+  $a = memory_get_usage(true);
+  test();
+  $b = memory_get_usage(true);
+  test();
+  $c = memory_get_usage(true);
+  $v1 = $b - $a;
+  $v2 = ($c - $b) * 10;
+  if ($v2 <= $v1) {
+    echo "Ok\n";
+  } else {
+    echo "strtotime is leaking: $a, $b, $c\n";
+  }
+}
+
+var_dump(strtotime("10 September 2000 UTC"));
+var_dump(strtotime("null"));
+
+main();

hphp/test/slow/ext_datetime/strtotime_leak.php.expect

@@ -0,0 +1,3 @@
+int(968544000)
+bool(false)
+Ok