From accce27e08a353124c9962704a3661bbccf1d942 Mon Sep 17 00:00:00 2001
From: Marc Horowitz <mhorowitz@fb.com>
Date: Wed, 3 Sep 2014 19:32:36 -0700
Subject: [PATCH] fix exceptionStr to work for derived classes of
 std::exception

Summary:
templates and overloads are hard.  This uses SFINAE to get
the desired behavior, and includes a test.

This also removes a hack in ExceptionWrapper which isn't needed with this fix.

Test Plan: string_test, exception_wrapper_test

Reviewed By: andrei.alexandrescu@fb.com

Subscribers: dreiss, dancol, njormrod

FB internal diff: D1535681

Blame Revision: D1517701
---
 folly/ExceptionWrapper.h  |  3 +--
 folly/String.h            | 18 ++++++++++--------
 folly/test/StringTest.cpp |  7 +++++++
 3 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/folly/ExceptionWrapper.h b/folly/ExceptionWrapper.h
index 14f2b71b..08082232 100644
--- a/folly/ExceptionWrapper.h
+++ b/folly/ExceptionWrapper.h
@@ -275,8 +275,7 @@ class try_and_catch<LastException, Exceptions...> :
   typename std::enable_if<std::is_base_of<std::exception, Ex>::value>::type
   assign_eptr(Ex& e) {
     this->eptr_ = std::current_exception();
-    // The cast is needed so we get the desired overload of exceptionStr()
-    this->estr_ = exceptionStr(static_cast<std::exception&>(e)).toStdString();
+    this->estr_ = exceptionStr(e).toStdString();
   }
 
   template <typename Ex>
diff --git a/folly/String.h b/folly/String.h
index 223c4907..14fda430 100644
--- a/folly/String.h
+++ b/folly/String.h
@@ -349,15 +349,9 @@ std::string hexDump(const void* ptr, size_t size);
 fbstring errnoStr(int err);
 
 /**
- * Debug string for an exception: include type and what().  Note that
- * the non-templated function overloads will be used in preference to
- * the template.
+ * Debug string for an exception: include type and what(), if
+ * defined.
  */
-template<typename T>
-fbstring exceptionStr(const T& e) {
-  return folly::to<fbstring>(demangle(typeid(e)));
-}
-
 inline fbstring exceptionStr(const std::exception& e) {
   return folly::to<fbstring>(demangle(typeid(e)), ": ", e.what());
 }
@@ -372,6 +366,14 @@ inline fbstring exceptionStr(std::exception_ptr ep) {
   }
 }
 
+template<typename E>
+auto exceptionStr(const E& e)
+  -> typename std::enable_if<!std::is_base_of<std::exception, E>::value,
+                             fbstring>::type
+{
+  return folly::to<fbstring>(demangle(typeid(e)));
+}
+
 /*
  * Split a string into a list of tokens by delimiter.
  *
diff --git a/folly/test/StringTest.cpp b/folly/test/StringTest.cpp
index f2162567..111945e8 100644
--- a/folly/test/StringTest.cpp
+++ b/folly/test/StringTest.cpp
@@ -1077,6 +1077,13 @@ TEST(String, humanify) {
   EXPECT_EQ("0x61ffffffffff", humanify(string("a\xff\xff\xff\xff\xff")));
 }
 
+TEST(String, exceptionStr) {
+  EXPECT_EQ(exceptionStr(0), "int");
+  EXPECT_EQ(exceptionStr(std::exception()), "std::exception: std::exception");
+  EXPECT_EQ(exceptionStr(std::runtime_error("folly")),
+            "std::runtime_error: folly");
+}
+
 namespace {
 
 /**
-- 
2.34.1