Allow android::base::ScopeGuard in STL containers

This change lets android::base::ScopeGuard be useful in STL containers
(e.g. std::vector<android::base::ScopeGuard<std::function<void()>>>). It
also provides perfect forwarding for android::base::make_scope_guard.

Bug: 34764308
Test: libbase_test

Change-Id: I7d1e5494b0f0695763cff0700efdb9ec18ae85c8
Merged-In: I7d1e5494b0f0695763cff0700efdb9ec18ae85c8
(cherry picked from commit b77035b89a3e95358a1aac9e28cd61c8b256e7ae)

include/android-base/scopeguard.h

diff --git a/include/android-base/scopeguard.h b/include/android-base/scopeguard.h
index abcf4bc..c314e02 100644
--- a/include/android-base/scopeguard.h
+++ b/include/android-base/scopeguard.h
@@ -17,20 +17,27 @@
 #ifndef ANDROID_BASE_SCOPEGUARD_H
 #define ANDROID_BASE_SCOPEGUARD_H
 
-#include <utility>  // for std::move
+#include <utility>  // for std::move, std::forward
 
 namespace android {
 namespace base {
 
+// ScopeGuard ensures that the specified functor is executed no matter how the
+// current scope exits.
 template <typename F>
 class ScopeGuard {
  public:
-  ScopeGuard(F f) : f_(f), active_(true) {}
+  ScopeGuard(F&& f) : f_(std::forward<F>(f)), active_(true) {}
 
   ScopeGuard(ScopeGuard&& that) : f_(std::move(that.f_)), active_(that.active_) {
     that.active_ = false;
   }
 
+  template <typename Functor>
+  ScopeGuard(ScopeGuard<Functor>&& that) : f_(std::move(that.f_)), active_(that.active_) {
+    that.active_ = false;
+  }
+
   ~ScopeGuard() {
     if (active_) f_();
   }
@@ -45,13 +52,16 @@
   bool active() const { return active_; }
 
  private:
+  template <typename Functor>
+  friend class ScopeGuard;
+
   F f_;
   bool active_;
 };
 
-template <typename T>
-ScopeGuard<T> make_scope_guard(T f) {
-  return ScopeGuard<T>(f);
+template <typename F>
+ScopeGuard<F> make_scope_guard(F&& f) {
+  return ScopeGuard<F>(std::forward<F>(f));
 }
 
 }  // namespace base

scopeguard_test.cpp

diff --git a/scopeguard_test.cpp b/scopeguard_test.cpp
index e11154a..9236d7b 100644
--- a/scopeguard_test.cpp
+++ b/scopeguard_test.cpp
@@ -17,6 +17,7 @@
 #include "android-base/scopeguard.h"
 
 #include <utility>
+#include <vector>
 
 #include <gtest/gtest.h>
 
@@ -44,3 +45,15 @@
   EXPECT_FALSE(scopeguard.active());
   ASSERT_FALSE(guarded_var);
 }
+
+TEST(scopeguard, vector) {
+  int guarded_var = 0;
+  {
+    std::vector<android::base::ScopeGuard<std::function<void()>>> scopeguards;
+    scopeguards.emplace_back(android::base::make_scope_guard(
+        std::bind([](int& guarded_var) { guarded_var++; }, std::ref(guarded_var))));
+    scopeguards.emplace_back(android::base::make_scope_guard(
+        std::bind([](int& guarded_var) { guarded_var++; }, std::ref(guarded_var))));
+  }
+  ASSERT_EQ(guarded_var, 2);
+}