libstdc++: Check for invalid syntax_option_type values in <regex>

The standard says that it is invalid for more than one grammar element
to be set in a value of type regex_constants::syntax_option_type. This
adds a check in the regex compiler andthrows an exception if an invalid
value is used.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/bits/regex_compiler.h (_Compiler::_S_validate): New
	function.
	* include/bits/regex_compiler.tcc (_Compiler::_Compiler): Use
	_S_validate to check flags.
	* include/bits/regex_error.h (_S_grammar): New error code for
	internal use.
	* testsuite/28_regex/basic_regex/ctors/grammar.cc: New test.

libstdc++-v3/include/bits/regex_compiler.h

@@ -143,6 +143,26 @@ namespace __detail
 	return ret;
       }
 
+      static _FlagT
+      _S_validate(_FlagT __f)
+      {
+	using namespace regex_constants;
+	switch (__f & (ECMAScript|basic|extended|awk|grep|egrep))
+	  {
+	  case ECMAScript:
+	  case basic:
+	  case extended:
+	  case awk:
+	  case grep:
+	  case egrep:
+	    return __f;
+	  case _FlagT(0):
+	    return __f | ECMAScript;
+	  default:
+	    std::__throw_regex_error(_S_grammar, "conflicting grammar options");
+	  }
+      }
+
       _FlagT              _M_flags;
       _ScannerT           _M_scanner;
       shared_ptr<_RegexT> _M_nfa;

libstdc++-v3/include/bits/regex_compiler.tcc

@@ -65,15 +65,7 @@ namespace __detail
     _Compiler<_TraitsT>::
     _Compiler(const _CharT* __b, const _CharT* __e,
 	      const typename _TraitsT::locale_type& __loc, _FlagT __flags)
-    : _M_flags((__flags
+    : _M_flags(_S_validate(__flags)),
-		& (regex_constants::ECMAScript
-		   | regex_constants::basic
-		   | regex_constants::extended
-		   | regex_constants::grep
-		   | regex_constants::egrep
-		   | regex_constants::awk))
-	       ? __flags
-	       : __flags | regex_constants::ECMAScript),
       _M_scanner(__b, __e, _M_flags, __loc),
       _M_nfa(make_shared<_RegexT>(__loc, _M_flags)),
       _M_traits(_M_nfa->_M_traits),

libstdc++-v3/include/bits/regex_error.h

@@ -61,7 +61,8 @@ namespace regex_constants
       _S_error_badrepeat,
       _S_error_complexity,
       _S_error_stack,
-      _S_null
+      _S_null,
+      _S_grammar
     };
 
   /** The expression contained an invalid collating element name. */

libstdc++-v3/testsuite/28_regex/basic_regex/ctors/grammar.cc

@@ -0,0 +1,53 @@
+// { dg-do run { target c++11 } }
+#include <regex>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  std::regex re{""};
+  VERIFY( re.flags() & std::regex::ECMAScript );
+
+  std::regex re2{"", std::regex::flag_type{}};
+  VERIFY( re2.flags() == std::regex::flag_type() ); // See also PR 83598
+}
+
+void
+test02()
+{
+  // A valid value of type syntax_option_type shall have at most one of the
+  // grammar elements ECMAScript, basic, extended, awk, grep, egrep, set.
+
+  try
+  {
+    std::regex{"", std::regex::ECMAScript|std::regex::basic};
+    VERIFY( false );
+  }
+  catch (const std::regex_error&)
+  {
+  }
+
+  try
+  {
+    std::regex{"", std::regex::extended|std::regex::basic};
+    VERIFY( false );
+  }
+  catch (const std::regex_error&)
+  {
+  }
+
+  try
+  {
+    std::regex{"", std::regex::grep|std::regex::basic};
+    VERIFY( false );
+  }
+  catch (const std::regex_error&)
+  {
+  }
+}
+
+int main()
+{
+  test01();
+  test02();
+}