util/Exception: move code to AppendNestedMessage()

src/util/Exception.cxx

@@ -29,21 +29,35 @@
 
 #include "Exception.hxx"
 
-std::string
-GetFullMessage(const std::exception &e,
+template<typename T>
+static void
+AppendNestedMessage(std::string &result, T &&e,
 		    const char *fallback, const char *separator) noexcept
 {
 	try {
-		std::rethrow_if_nested(e);
-		return e.what();
+		std::rethrow_if_nested(std::forward<T>(e));
+	} catch (const std::exception &nested) {
+		result += separator;
+		result += nested.what();
+		AppendNestedMessage(result, nested, fallback, separator);
+	} catch (const std::nested_exception &ne) {
+		AppendNestedMessage(result, ne, fallback, separator);
 	} catch (...) {
-		return std::string(e.what()) + separator +
-			GetFullMessage(std::current_exception(),
-				       fallback, separator);
+		result += separator;
+		result += fallback;
 	}
 }
 
 std::string
+GetFullMessage(const std::exception &e,
+	       const char *fallback, const char *separator) noexcept
+{
+	std::string result = e.what();
+	AppendNestedMessage(result, e, fallback, separator);
+	return result;
+}
+
+std::string
 GetFullMessage(std::exception_ptr ep,
 	       const char *fallback, const char *separator) noexcept
 {
@@ -53,7 +67,7 @@ GetFullMessage(std::exception_ptr ep,
 		return GetFullMessage(e, fallback, separator);
 	} catch (const std::nested_exception &ne) {
 		return GetFullMessage(ne.nested_ptr(), fallback, separator);
-	}
-
+	} catch (...) {
 		return fallback;
+	}
 }