util/Exception: add GetFullMessage(std::exception)

src/util/Exception.cxx

@@ -29,6 +29,20 @@
 
 #include "Exception.hxx"
 
+std::string
+GetFullMessage(const std::exception &e,
+	       const char *fallback, const char *separator) noexcept
+{
+	try {
+		std::rethrow_if_nested(e);
+		return e.what();
+	} catch (...) {
+		return std::string(e.what()) + separator +
+			GetFullMessage(std::current_exception(),
+				       fallback, separator);
+	}
+}
+
 std::string
 GetFullMessage(std::exception_ptr ep,
 	       const char *fallback, const char *separator) noexcept
@@ -36,14 +50,7 @@ GetFullMessage(std::exception_ptr ep,
 	try {
 		std::rethrow_exception(ep);
 	} catch (const std::exception &e) {
-		try {
+		return GetFullMessage(e, fallback, separator);
-			std::rethrow_if_nested(e);
-			return e.what();
-		} catch (...) {
-			return std::string(e.what()) + separator +
-				GetFullMessage(std::current_exception(),
-					       fallback, separator);
-		}
 	} catch (const std::nested_exception &ne) {
 		return GetFullMessage(ne.nested_ptr(), fallback, separator);
 	}

src/util/Exception.hxx

@@ -33,6 +33,15 @@
 #include <exception>
 #include <string>
 
+/**
+ * Obtain the full concatenated message of an exception and its nested
+ * chain.
+ */
+std::string
+GetFullMessage(const std::exception &e,
+	       const char *fallback="Unknown exception",
+	       const char *separator="; ") noexcept;
+
 /**
  * Extract the full message of a C++ exception, considering its nested
  * exceptions (if any).