[liveness] Do not report on variables with block attribute

Reviewed By: sblackshear

Differential Revision: D6408338

fbshipit-source-id: 0fac3be

infer/src/checkers/liveness.ml

@@ -126,7 +126,7 @@ let checker {Callbacks.tenv; summary; proc_desc} : Specs.summary =
     not
       ( Pvar.is_frontend_tmp pvar || Pvar.is_return pvar || Pvar.is_global pvar
       || Domain.mem (Var.of_pvar pvar) live_vars || Procdesc.is_captured_var proc_desc pvar
-      || is_scope_guard typ )
+      || is_scope_guard typ || Procdesc.has_modify_in_block_attr proc_desc pvar )
   in
   let log_report pvar loc =
     let issue_id = IssueType.dead_store.unique_id in

infer/tests/codetoanalyze/objc/liveness/ObserverExample.m

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2014 - present Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import <Foundation/Foundation.h>
+
+@interface ObervserExample : NSObject
+
+@end
+
+@implementation ObervserExample
+
+- (void)observer_no_dead_store:(id)object {
+  __block id observer = [[NSNotificationCenter defaultCenter]
+      addObserverForName:nil
+                  object:object
+                   queue:nil
+              usingBlock:^(NSNotification* note) {
+                [[NSNotificationCenter defaultCenter] removeObserver:observer
+                                                                name:nil
+                                                              object:nil];
+              }];
+}
+
+@end