[libc++][format] Fixes out of bounds access.

[Mordante]

Summary

Fixes https://llvm.org/PR65011

[Mordante]

libcxx/test/std/utilities/format/format.functions/vformat.pass.cpp

53–60

Guard this block for the no-execption build.

[ldionne]

This should be backported to release/17.x!

[Mordante]

Rebased and addressed review comments

[Mordante]

Retrigger CI.

libcxx/include/__format/format_functions.h

 
 template <contiguous_iterator _Iterator, class _ParseCtx, class _Ctx>
 _LIBCPP_HIDE_FROM_ABI constexpr _Iterator
 __handle_replacement_field(_Iterator __begin, _Iterator __end,
                            _ParseCtx& __parse_ctx, _Ctx& __ctx) {
   using _CharT = iter_value_t<_Iterator>;
   __format::__parse_number_result __r = __format::__parse_arg_id(__begin, __end, __parse_ctx);
 
+  if (__r.__last == __end)
+    std::__throw_format_error("The argument index should end with a ':' or a '}'");
+
   bool __parse = *__r.__last == _CharT(':');
   switch (*__r.__last) {
   case _CharT(':'):
     // The arg-id has a format-specifier, advance the input to the format-spec.
     __parse_ctx.advance_to(__r.__last + 1);
     break;
   case _CharT('}'):
     // The arg-id has no format-specifier.

libcxx/test/std/utilities/format/format.functions/format_tests.h

void format_tests(TestFunction check, ExceptionTest check_exception) {
   // *** Test buffer boundaries format strings ***
   if constexpr (modus == execution_modus::full) {
     format_test_buffer_copy<CharT>(check);
     format_test_buffer_full<CharT>(check);
   }
 
   // *** Test invalid format strings ***
   check_exception("The format string terminates at a '{'", SV("{"));
+  check_exception("The argument index value is too large for the number of arguments supplied", SV("{:"));
   check_exception("The replacement field misses a terminating '}'", SV("{:"), 42);
 
+  check_exception("The argument index should end with a ':' or a '}'", SV("{0"));
+  check_exception("The argument index value is too large for the number of arguments supplied", SV("{0:"));
+  check_exception("The replacement field misses a terminating '}'", SV("{0:"), 42);
+
   check_exception("The format string contains an invalid escape sequence", SV("}"));
   check_exception("The format string contains an invalid escape sequence", SV("{:}-}"), 42);
 
   check_exception("The format string contains an invalid escape sequence", SV("} "));
   check_exception("The argument index starts with an invalid character", SV("{-"), 42);
   check_exception("The argument index value is too large for the number of arguments supplied", SV("hello {}"));
   check_exception("The argument index value is too large for the number of arguments supplied", SV("hello {0}"));
   check_exception("The argument index value is too large for the number of arguments supplied", SV("hello {1}"), 42);

libcxx/test/std/utilities/format/format.functions/vformat.pass.cpp

[]<class CharT, class... Args>(
                 e.what() == what,
                 TEST_WRITE_CONCATENATED(
                     "\nFormat string   ", fmt, "\nExpected exception ", what, "\nActual exception   ", e.what(), '\n'));
           },
           TEST_IGNORE_NODISCARD std::vformat(fmt, std::make_format_args<context_t<CharT>>(args...)));
     };
 
 int main(int, char**) {
+  // reproducer of https://llvm.org/PR65011
+  try {
+    const char fmt[] = {'{', '0'};
+    char buf[4096];
+    [[maybe_unused]] auto ignored =
+        std::vformat_to(buf, std::string_view{fmt, fmt + sizeof(fmt)}, std::make_format_args());
+  } catch (...) {
+  }
+
   format_tests<char, execution_modus::full>(test, test_exception);
 
 #ifndef TEST_HAS_NO_WIDE_CHARACTERS
   format_tests_char_to_wchar_t(test);
   format_tests<wchar_t, execution_modus::full>(test, test_exception);
 #endif
 
   return 0;
 }