From 0ebdd369b018edb28e9cc79abbf21dbeb9dda8f3 Mon Sep 17 00:00:00 2001
From: Sam Blackshear <shb@fb.com>
Date: Tue, 5 Dec 2017 08:36:39 -0800
Subject: [PATCH] [liveness] don't warn on dead stores of type CKComponentScope

Summary: Local `CKComponentScope`'s are often created purely for their side effects, so it's fine for them to be unread.

Reviewed By: jeremydubreil

Differential Revision: D6475475

fbshipit-source-id: 17e869a
---
 infer/src/checkers/liveness.ml                |  7 ++++--
 .../objc/liveness/CoreFoundationExample.m     | 25 +++++++++++++++++++
 .../codetoanalyze/objc/liveness/Makefile      |  2 +-
 3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/infer/src/checkers/liveness.ml b/infer/src/checkers/liveness.ml
index 6a1369b6a..83e94bdbc 100644
--- a/infer/src/checkers/liveness.ml
+++ b/infer/src/checkers/liveness.ml
@@ -103,13 +103,15 @@ let checker {Callbacks.tenv; summary; proc_desc} : Specs.summary =
   in
   let matcher_scope_guard =
     QualifiedCppName.Match.of_fuzzy_qual_names
-      [ "folly::RWSpinLock::ReadHolder"
+      [ (* C++ *)
+        "folly::RWSpinLock::ReadHolder"
       ; "folly::RWSpinLock::WriteHolder"
       ; "folly::SpinLockGuard"
       ; "folly::ScopeGuard"
       ; "std::lock_guard"
       ; "std::scoped_lock"
-      ; "std::unique_lock" ]
+      ; "std::unique_lock" (* Obj-C *)
+      ; "CKComponentScope" ]
   in
   (* It's fine to have a dead store on a type that uses the "scope guard" pattern. These types
      are only read in their destructors, and this is expected/ok.
@@ -160,3 +162,4 @@ let checker {Callbacks.tenv; summary; proc_desc} : Specs.summary =
   in
   List.iter (CFG.nodes cfg) ~f:report_on_node ;
   summary
+
diff --git a/infer/tests/codetoanalyze/objc/liveness/CoreFoundationExample.m b/infer/tests/codetoanalyze/objc/liveness/CoreFoundationExample.m
index 32f0a1750..5e3655a62 100644
--- a/infer/tests/codetoanalyze/objc/liveness/CoreFoundationExample.m
+++ b/infer/tests/codetoanalyze/objc/liveness/CoreFoundationExample.m
@@ -15,3 +15,28 @@ static NSDictionary* dictionaryRepresentationFromCFPreferences(
   return (__bridge_transfer NSDictionary*)CFPreferencesCopyMultiple(
       NULL, ID, kCFPreferencesCurrentUser, kCFPreferencesAnyHost);
 }
+
+// mock for testing
+class CKComponentScope {
+ public:
+  CKComponentScope(Class __unsafe_unretained componentClass,
+                   id identifier = nil,
+                   id (^initialStateCreator)(void) = nil);
+  ~CKComponentScope();
+  int a;
+
+ private:
+  CKComponentScope(const CKComponentScope&) = delete;
+  CKComponentScope& operator=(const CKComponentScope&) = delete;
+};
+
+@interface ScopeTest : NSObject
+@end
+
+@implementation ScopeTest
+
++ (void)dead_ckcomponentscope_ok {
+  CKComponentScope scope(self); // created for side effects; should not warn
+}
+
+@end
diff --git a/infer/tests/codetoanalyze/objc/liveness/Makefile b/infer/tests/codetoanalyze/objc/liveness/Makefile
index 9ace83b1f..f16c7bbea 100644
--- a/infer/tests/codetoanalyze/objc/liveness/Makefile
+++ b/infer/tests/codetoanalyze/objc/liveness/Makefile
@@ -8,7 +8,7 @@
 TESTS_DIR = ../../..
 
 ANALYZER = checkers
-CLANG_OPTIONS = -x objective-c -c
+CLANG_OPTIONS = -x objective-c++ -std=c++11 -fobjc-arc -c
 INFER_OPTIONS = --liveness-only --debug-exceptions --project-root $(TESTS_DIR)
 INFERPRINT_OPTIONS = --issues-tests