From b4e6ab95b22fb44ecf578f19677876fea4832cc6 Mon Sep 17 00:00:00 2001
From: "Tao Chen (RPC)" <ctao@meta.com>
Date: Mon, 13 Jan 2025 23:49:43 -0800
Subject: [PATCH] Parse and save the name from a named creator

Differential Revision: D68113986

fbshipit-source-id: a413040eaf9e0bdb1f46c57597d0843a0bbeadf1
---
 folly/observer/Observer-inl.h        | 10 ++++++----
 folly/observer/Observer.h            |  5 +++++
 folly/observer/detail/Core.h         | 22 ++++++++++++++++++++++
 folly/observer/test/ObserverTest.cpp | 28 ++++++++++++++++++++++++++++
 4 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/folly/observer/Observer-inl.h b/folly/observer/Observer-inl.h
index b3b38443e7a..5b5aac06683 100644
--- a/folly/observer/Observer-inl.h
+++ b/folly/observer/Observer-inl.h
@@ -26,7 +26,7 @@ observer::Observer<ResultOfUnwrapSharedPtr<F>> makeObserver(
     F&& creator,
     std::optional<Core::CreatorContext> creatorContext = std::nullopt) {
   if (!creatorContext) {
-    creatorContext = Core::CreatorContext{&typeid(F)};
+    creatorContext = Core::CreatorContext::create(std::forward<F>(creator));
   }
   auto core = Core::create(
       [creator_2 = std::forward<F>(creator)]() mutable {
@@ -41,11 +41,12 @@ observer::Observer<ResultOfUnwrapSharedPtr<F>> makeObserver(
 
 template <typename F>
 observer::Observer<ResultOfNoObserverUnwrap<F>> makeObserver(F&& creator) {
+  auto creatorContext = Core::CreatorContext::create(std::forward<F>(creator));
   return makeObserver(
       [creator_2 = std::forward<F>(creator)]() mutable {
         return std::make_shared<ResultOfNoObserverUnwrap<F>>(creator_2());
       },
-      Core::CreatorContext{&typeid(F)});
+      std::move(creatorContext));
 }
 
 template <typename F>
@@ -53,7 +54,7 @@ observer::Observer<ResultOfUnwrapSharedPtr<F>> makeValueObserver(
     F&& creator,
     std::optional<Core::CreatorContext> creatorContext = std::nullopt) {
   if (!creatorContext) {
-    creatorContext = Core::CreatorContext{&typeid(F)};
+    creatorContext = Core::CreatorContext::create(std::forward<F>(creator));
   }
   return makeObserver(
       [activeValue = std::shared_ptr<const ResultOfUnwrapSharedPtr<F>>(),
@@ -69,11 +70,12 @@ observer::Observer<ResultOfUnwrapSharedPtr<F>> makeValueObserver(
 
 template <typename F>
 observer::Observer<ResultOfNoObserverUnwrap<F>> makeValueObserver(F&& creator) {
+  auto creatorContext = Core::CreatorContext::create(std::forward<F>(creator));
   return makeValueObserver(
       [creator_2 = std::forward<F>(creator)]() mutable {
         return std::make_shared<ResultOfNoObserverUnwrap<F>>(creator_2());
       },
-      Core::CreatorContext{&typeid(F)});
+      std::move(creatorContext));
 }
 } // namespace observer_detail
 
diff --git a/folly/observer/Observer.h b/folly/observer/Observer.h
index 0dcf06a6378..5570ad0960d 100644
--- a/folly/observer/Observer.h
+++ b/folly/observer/Observer.h
@@ -249,6 +249,11 @@ class Observer {
   const std::type_info* getCreatorTypeInfo() const {
     return core_->getCreatorContext().typeInfo;
   }
+
+  const std::string& getCreatorName() const {
+    return core_->getCreatorContext().name;
+  }
+
   folly::observer_detail::Core& getCore() const { return *core_; }
 
  private:
diff --git a/folly/observer/detail/Core.h b/folly/observer/detail/Core.h
index fcd00565d78..9580a4c0341 100644
--- a/folly/observer/detail/Core.h
+++ b/folly/observer/detail/Core.h
@@ -30,6 +30,17 @@
 namespace folly {
 namespace observer_detail {
 
+#define DEFINE_HAS_MEMBER_FUNC(Member)                                         \
+  template <typename T, typename = std::void_t<>>                              \
+  struct Has_##Member##T : std::false_type {};                                 \
+  template <typename T>                                                        \
+  struct Has_##Member##T<T, std::void_t<decltype(std::declval<T>().Member())>> \
+      : std::true_type {};                                                     \
+  template <typename T>                                                        \
+  constexpr bool Has_##Member##T_v = Has_##Member##T<T>::value;
+
+DEFINE_HAS_MEMBER_FUNC(getName)
+
 class ObserverManager;
 
 /**
@@ -43,6 +54,17 @@ class Core : public std::enable_shared_from_this<Core> {
 
   struct CreatorContext {
     const std::type_info* typeInfo;
+    std::string name;
+
+    template <typename F>
+    static CreatorContext create(const F& creator) {
+      CreatorContext context;
+      context.typeInfo = &typeid(F);
+      if constexpr (Has_getNameT_v<F>) {
+        context.name = creator.getName();
+      }
+      return context;
+    }
   };
   /**
    * Blocks until creator is successfully run by ObserverManager
diff --git a/folly/observer/test/ObserverTest.cpp b/folly/observer/test/ObserverTest.cpp
index aace87638ee..dfcc1415605 100644
--- a/folly/observer/test/ObserverTest.cpp
+++ b/folly/observer/test/ObserverTest.cpp
@@ -42,6 +42,18 @@ namespace {
 template <typename T>
 struct AltAtomic : std::atomic<T> {};
 
+template <typename F>
+struct NamedCreator {
+  std::string name;
+  F creator;
+
+  NamedCreator(std::string nameP, F&& creatorP)
+      : name(std::move(nameP)), creator(std::forward<F>(creatorP)) {}
+
+  const std::string& getName() const { return name; }
+
+  auto operator()() const { return creator(); }
+};
 } // namespace
 
 namespace folly {
@@ -1293,5 +1305,21 @@ TEST(Observer, TestSimpleObservableWithTypeInfo) {
       StartsWith(prefix));
 }
 
+TEST(Observer, TestObserverWithNamedCreator) {
+  {
+    auto observer =
+        folly::observer::makeObserver(NamedCreator("foo", [] { return 42; }));
+    EXPECT_EQ(42, **observer);
+    EXPECT_EQ(observer.getCreatorName(), "foo");
+  }
+  {
+    auto observer = folly::observer::makeValueObserver(NamedCreator("foo", [] {
+      return 42;
+    }));
+    EXPECT_EQ(42, **observer);
+    EXPECT_EQ(observer.getCreatorName(), "foo");
+  }
+}
+
 } // namespace observer
 } // namespace folly