[libc++][regex] Validate backreferences in the constructor.

This patch enables throwing exceptions for invalid backreferences
in the constructor when using the basic, extended,  grep, or egrep grammar.

This fixes bug 34297.

Differential Revision: https://reviews.llvm.org/D62453

libcxx/include/regex

@@ -4661,6 +4661,8 @@ basic_regex<_CharT, _Traits>::__test_back_ref(_CharT c)
     unsigned __val = __traits_.value(c, 10);
     if (__val >= 1 && __val <= 9)
     {
+        if (__val > mark_count())
+            __throw_regex_error<regex_constants::error_backref>();
         __push_back_ref(__val);
         return true;
     }

libcxx/test/std/re/re.regex/re.regex.construct/bad_backref.pass.cpp

@@ -18,11 +18,11 @@
 #include <cassert>
 #include "test_macros.h"
 
-static bool error_badbackref_thrown(const char *pat)
+static bool error_badbackref_thrown(const char *pat, std::regex::flag_type f)
 {
     bool result = false;
     try {
-        std::regex re(pat);
+        std::regex re(pat, f);
     } catch (const std::regex_error &ex) {
         result = (ex.code() == std::regex_constants::error_backref);
     }
@@ -31,9 +31,25 @@ static bool error_badbackref_thrown(const char *pat)
 
 int main(int, char**)
 {
-    assert(error_badbackref_thrown("\\1abc"));      // no references
-    assert(error_badbackref_thrown("ab(c)\\2def")); // only one reference
-    assert(error_badbackref_thrown("\\800000000000000000000000000000")); // overflows
+//  no references
+    assert(error_badbackref_thrown("\\1abc", std::regex_constants::ECMAScript));
+    assert(error_badbackref_thrown("\\1abd", std::regex::basic));
+    assert(error_badbackref_thrown("\\1abd", std::regex::extended));
+    assert(error_badbackref_thrown("\\1abd", std::regex::awk) == false);
+    assert(error_badbackref_thrown("\\1abd", std::regex::grep));
+    assert(error_badbackref_thrown("\\1abd", std::regex::egrep));
+
+//  only one reference
+    assert(error_badbackref_thrown("ab(c)\\2def", std::regex_constants::ECMAScript));
+    assert(error_badbackref_thrown("ab\\(c\\)\\2def", std::regex_constants::basic));
+    assert(error_badbackref_thrown("ab(c)\\2def", std::regex_constants::extended));
+    assert(error_badbackref_thrown("ab\\(c\\)\\2def", std::regex_constants::awk) == false);
+    assert(error_badbackref_thrown("ab(c)\\2def", std::regex_constants::awk) == false);
+    assert(error_badbackref_thrown("ab\\(c\\)\\2def", std::regex_constants::grep));
+    assert(error_badbackref_thrown("ab(c)\\2def", std::regex_constants::egrep));
+
+
+    assert(error_badbackref_thrown("\\800000000000000000000000000000", std::regex_constants::ECMAScript)); // overflows
 
 //  this should NOT throw, because we only should look at the '1'
 //  See https://bugs.llvm.org/show_bug.cgi?id=31387
@@ -42,5 +58,35 @@ int main(int, char**)
     std::regex re(pat1, pat1 + 7); // extra chars after the end.
     }
 
+//  reference before group
+    assert(error_badbackref_thrown("\\1(abc)", std::regex_constants::ECMAScript));
+    assert(error_badbackref_thrown("\\1\\(abd\\)", std::regex::basic));
+    assert(error_badbackref_thrown("\\1(abd)", std::regex::extended));
+    assert(error_badbackref_thrown("\\1(abd)", std::regex::awk) == false);
+    assert(error_badbackref_thrown("\\1\\(abd\\)", std::regex::awk) == false);
+    assert(error_badbackref_thrown("\\1\\(abd\\)", std::regex::grep));
+    assert(error_badbackref_thrown("\\1(abd)", std::regex::egrep));
+
+//  reference limit
+    assert(error_badbackref_thrown("(cat)\\10", std::regex::ECMAScript));
+    assert(error_badbackref_thrown("\\(cat\\)\\10", std::regex::basic) == false);
+    assert(error_badbackref_thrown("(cat)\\10", std::regex::extended) == false);
+    assert(error_badbackref_thrown("\\(cat\\)\\10", std::regex::awk) == false);
+    assert(error_badbackref_thrown("(cat)\\10", std::regex::awk) == false);
+    assert(error_badbackref_thrown("\\(cat\\)\\10", std::regex::grep) == false);
+    assert(error_badbackref_thrown("(cat)\\10", std::regex::egrep) == false);
+
+//  https://bugs.llvm.org/show_bug.cgi?id=34297
+    assert(error_badbackref_thrown("(cat)\\1", std::regex::basic));
+    assert(error_badbackref_thrown("\\(cat\\)\\1", std::regex::basic) == false);
+    assert(error_badbackref_thrown("(cat)\\1", std::regex::extended) == false);
+    assert(error_badbackref_thrown("\\(cat\\)\\1", std::regex::extended));
+    assert(error_badbackref_thrown("(cat)\\1", std::regex::awk) == false);
+    assert(error_badbackref_thrown("\\(cat\\)\\1", std::regex::awk) == false);
+    assert(error_badbackref_thrown("(cat)\\1", std::regex::grep));
+    assert(error_badbackref_thrown("\\(cat\\)\\1", std::regex::grep) == false);
+    assert(error_badbackref_thrown("(cat)\\1", std::regex::egrep) == false);
+    assert(error_badbackref_thrown("\\(cat\\)\\1", std::regex::egrep));
+
   return 0;
 }