From 4e7efffdcadf373d1ae7d17722634d3a849c1f7a Mon Sep 17 00:00:00 2001
From: Yedidya Feldblum <yfeldblum@fb.com>
Date: Sun, 2 May 2021 12:05:49 -0700
Subject: [PATCH] revise exceptionStr

Summary: Revise all overloads of `folly::exceptionStr` in terms of `type_info_of`, `exception_ptr_get_type`, and `exception_ptr_get_object`. No longer rely on `catch_exception` and no longer have inline preprocessor conditionals.

Reviewed By: Orvid, luciang

Differential Revision: D26333081

fbshipit-source-id: 318ce83b9f15a12d5a33f528134e6fb38bb78a62
---
 folly/ExceptionString.cpp          | 65 ++++++++----------------------
 folly/ExceptionString.h            |  4 +-
 folly/Executor.cpp                 | 12 ++----
 folly/Executor.h                   |  6 +--
 folly/test/ExceptionStringTest.cpp |  2 +-
 5 files changed, 24 insertions(+), 65 deletions(-)

diff --git a/folly/ExceptionString.cpp b/folly/ExceptionString.cpp
index b762cf316c6..356586c6650 100644
--- a/folly/ExceptionString.cpp
+++ b/folly/ExceptionString.cpp
@@ -18,67 +18,34 @@
 
 #include <utility>
 
-#include <folly/CPortability.h>
-#include <folly/CppAttributes.h>
 #include <folly/Demangle.h>
-#include <folly/functional/Invoke.h>
 #include <folly/lang/Exception.h>
+#include <folly/lang/TypeInfo.h>
 
 namespace folly {
 
+namespace {
+
+fbstring exception_string_type(std::type_info const* ti) {
+  return ti ? demangle(*ti) : "<unknown exception>";
+}
+
+} // namespace
+
 /**
  * Debug string for an exception: include type and what(), if
  * defined.
  */
-fbstring exceptionStr(const std::exception& e) {
-#if FOLLY_HAS_RTTI
-  fbstring rv(demangle(typeid(e)));
-  rv += ": ";
-#else
-  fbstring rv("Exception (no RTTI available): ");
-#endif
-  rv += e.what();
-  return rv;
+fbstring exceptionStr(std::exception const& e) {
+  auto prefix = exception_string_type(folly::type_info_of(e));
+  return std::move(prefix) + ": " + e.what();
 }
 
-namespace {
-
-FOLLY_CREATE_MEMBER_INVOKER(invoke_cxa_exception_type_fn, __cxa_exception_type);
-
-struct fallback_cxa_exception_type_fn {
-  FOLLY_MAYBE_UNUSED FOLLY_ERASE_HACK_GCC std::type_info const* operator()(
-      std::exception_ptr const&) const noexcept {
-    return nullptr;
-  }
-};
-
-using invoke_or_fallback_cxa_exception_type_fn = std::conditional_t<
-    is_invocable_r_v<
-        std::type_info const*,
-        invoke_cxa_exception_type_fn,
-        std::exception_ptr const&>,
-    invoke_cxa_exception_type_fn,
-    fallback_cxa_exception_type_fn>;
-
-FOLLY_INLINE_VARIABLE constexpr invoke_or_fallback_cxa_exception_type_fn
-    invoke_or_fallback_cxa_exception_type;
-
-} // namespace
-
-fbstring exceptionStr(std::exception_ptr ep) {
-  if (!kHasExceptions) {
-    return "Exception (catch unavailable)";
+fbstring exceptionStr(std::exception_ptr const& ep) {
+  if (auto ex = exception_ptr_get_object<std::exception>(ep)) {
+    return exceptionStr(*ex);
   }
-  auto type = invoke_or_fallback_cxa_exception_type(ep);
-  return catch_exception(
-      [&]() -> fbstring {
-        return catch_exception<std::exception const&>(
-            [&]() -> fbstring { std::rethrow_exception(std::move(ep)); },
-            static_cast<fbstring (&)(std::exception const&)>(exceptionStr));
-      },
-      [&]() -> fbstring {
-        return type ? demangle(*type) : "<unknown exception>";
-      });
+  return exception_string_type(exception_ptr_get_type(ep));
 }
 
 } // namespace folly
diff --git a/folly/ExceptionString.h b/folly/ExceptionString.h
index f287ceea7c1..078c6c26cd5 100644
--- a/folly/ExceptionString.h
+++ b/folly/ExceptionString.h
@@ -26,8 +26,8 @@ namespace folly {
  * Debug string for an exception: include type and what(), if
  * defined.
  */
-fbstring exceptionStr(const std::exception& e);
+fbstring exceptionStr(std::exception const& e);
 
-fbstring exceptionStr(std::exception_ptr ep);
+fbstring exceptionStr(std::exception_ptr const& ep);
 
 } // namespace folly
diff --git a/folly/Executor.cpp b/folly/Executor.cpp
index bc6e02aff8f..42adb28341b 100644
--- a/folly/Executor.cpp
+++ b/folly/Executor.cpp
@@ -26,15 +26,9 @@
 
 namespace folly {
 
-void Executor::invokeCatchingExnsLog(
-    char const* const prefix, std::exception const* const ex) {
-  auto const message = " threw unhandled ";
-  if (ex) {
-    LOG(ERROR) << prefix << message << exceptionStr(*ex);
-  } else {
-    auto ep = std::current_exception();
-    LOG(ERROR) << prefix << message << exceptionStr(ep);
-  }
+void Executor::invokeCatchingExnsLog(char const* const prefix) noexcept {
+  auto ep = std::current_exception();
+  LOG(ERROR) << prefix << " threw unhandled " << exceptionStr(ep);
 }
 
 void Executor::addWithPriority(Func, int8_t /* priority */) {
diff --git a/folly/Executor.h b/folly/Executor.h
index 45b74a75ed3..42e7d5d38f6 100644
--- a/folly/Executor.h
+++ b/folly/Executor.h
@@ -232,8 +232,7 @@ class Executor {
 
   template <typename F>
   FOLLY_ERASE static void invokeCatchingExns(char const* p, F f) noexcept {
-    auto h = [p](auto&... e) noexcept { invokeCatchingExnsLog(p, &e...); };
-    catch_exception([&] { catch_exception<std::exception const&>(f, h); }, h);
+    catch_exception(f, invokeCatchingExnsLog, p);
   }
 
  protected:
@@ -269,8 +268,7 @@ class Executor {
   }
 
  private:
-  static void invokeCatchingExnsLog(
-      char const* prefix, std::exception const* ex = nullptr);
+  static void invokeCatchingExnsLog(char const* prefix) noexcept;
 
   template <typename ExecutorT>
   static KeepAlive<ExecutorT> makeKeepAliveDummy(ExecutorT* executor) {
diff --git a/folly/test/ExceptionStringTest.cpp b/folly/test/ExceptionStringTest.cpp
index 39dfd080668..7209a99c3a5 100644
--- a/folly/test/ExceptionStringTest.cpp
+++ b/folly/test/ExceptionStringTest.cpp
@@ -30,7 +30,7 @@ TEST_F(ExceptionStringTest, exception_ptr) {
 
 TEST_F(ExceptionStringTest, exception_ptr_unknown) {
   auto ptr = std::make_exception_ptr(7);
-  auto expected = folly::kIsLibstdcpp ? "int" : "<unknown exception>";
+  auto expected = "int";
   auto actual = folly::exceptionStr(ptr).toStdString();
   EXPECT_EQ(expected, actual);
 }