Merge to upstream r225300.

Change-Id: I2b23715db9ac129ff80aa78ad5824db0a4d6fbb3

test/std/re/re.regex/re.regex.construct/bad_escape.pass.cpp

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <regex>
+
+// template <class charT, class traits = regex_traits<charT>> class basic_regex;
+
+// template <class ST, class SA>
+//    basic_regex(const basic_string<charT, ST, SA>& s);
+
+#include <regex>
+#include <cassert>
+
+static bool error_escape_thrown(const char *pat) 
+{
+    bool result = false;
+    try {
+        std::regex re(pat);
+    } catch (std::regex_error &ex) {
+        result = (ex.code() == std::regex_constants::error_escape);
+    }
+    return result;
+}
+
+int main() 
+{
+    assert(error_escape_thrown("[\\a]"));
+    assert(error_escape_thrown("\\a"));
+
+    assert(error_escape_thrown("[\\e]"));
+    assert(error_escape_thrown("\\e"));
+
+    assert(error_escape_thrown("[\\c:]"));
+    assert(error_escape_thrown("\\c:"));
+    assert(error_escape_thrown("\\c"));
+    assert(!error_escape_thrown("[\\cA]"));
+    assert(!error_escape_thrown("\\cA"));
+
+}