abort during getline in yyfill

[kevin--]

I'm experiencing a runtime abort with MSVC 2015 14.0.24720.00 Update 1 while attempting to read a file using the ">>" operator. The file was written by this library as well, using the "<<" operator.
A dialog appears with "abort() has been called", hitting retry drops me into the debugger.

I don't think there's anything very novel about my code:
json document; std::ifstream in; in.exceptions(std::ifstream::failbit | std::ifstream::badbit); in.open(filepath); in >> document;

For now the work around is to read the file into a string, then call parse()

here's the data I'm trying to read
file_in_question.json.txt

Stack trace
> bumped.exe!__GSHandlerCheck_EH(_EXCEPTION_RECORD * ExceptionRecord, void * EstablisherFrame, _CONTEXT * ContextRecord, _DISPATCHER_CONTEXT * DispatcherContext) Line 101 C

...bunch of msvc runtime...

bumped.exe!std::getline<char,std::char_traits<char>,std::allocator<char> >(std::basic_istream<char,std::char_traits<char> > && _Istr, std::basic_string<char,std::char_traits<char>,std::allocator<char> > & _Str, const char _Delim) Line 120 C++

bumped.exe!std::getline<char,std::char_traits<char>,std::allocator<char> >(std::basic_istream<char,std::char_traits<char> > & _Istr, std::basic_string<char,std::char_traits<char>,std::allocator<char> > & _Str) Line 162 C++

bumped.exe!nlohmann::basic_json<std::map,std::vector,std::basic_string<char,std::char_traits<char>,std::allocator<char> >,bool,__int64,double,std::allocator>::lexer::yyfill() Line 7636 C++

bumped.exe!nlohmann::basic_json<std::map,std::vector,std::basic_string<char,std::char_traits<char>,std::allocator<char> >,bool,__int64,double,std::allocator>::lexer::scan() Line 6877 C++

bumped.exe!nlohmann::basic_json<std::map,std::vector,std::basic_string<char,std::char_traits<char>,std::allocator<char> >,bool,__int64,double,std::allocator>::parser::get_token() Line 8118 C++

bumped.exe!nlohmann::basic_json<std::map,std::vector,std::basic_string<char,std::char_traits<char>,std::allocator<char> >,bool,__int64,double,std::allocator>::parser::parse_internal(bool keep) Line 7961 C++

bumped.exe!nlohmann::basic_json<std::map,std::vector,std::basic_string<char,std::char_traits<char>,std::allocator<char> >,bool,__int64,double,std::allocator>::parser::parse() Line 7889 C++

bumped.exe!nlohmann::operator>>(std::basic_istream<char,std::char_traits<char> > & i, nlohmann::basic_json<std::map,std::vector,std::basic_string<char,std::char_traits<char>,std::allocator<char> >,bool,__int64,double,std::allocator> & j) Line 5287 C++

[kevin--]

by the way, working from the v1.1.0 tag

[nlohmann]

Hi @kevin--, sorry about the bug. As I do not work with Windows/MSVC myself, it's difficult do dig deeper into the issue.

[kevin--]

I'll take a crack at it this week when I get a chance

[duncanwerner]

According to http://en.cppreference.com/w/cpp/string/basic_string/getline

If no characters were extracted for whatever reason (not even the discarded delimiter), getline sets failbit and returns.

it seems like there's always a call to yyfill at the end of the stream, so if you are masking failbit, it will throw an exception. As to why you're getting an abort(), perhaps you're using the wrong exception model?

[kevin--]

@duncanwerner good call. If I do not set the exception mask, then I do not get the abort. Still want to look at this, because my work around of reading into the string then parsing still works. Maybe that method does not use getline.

[nlohmann]

@duncanwerner Thanks for this note. I see if I can "force" this behavior on a system where I can debug.

[kevin--]

There are two points of failure, both related to calling std::getline

1. if the input file is empty (0 bytes), then the abort occurs on the first call to std::getline (2nd line of the explicit lexer(std::istream* s) noexcept constructor).
2. Otherwise, it happens when std::getline gets no content at the end of the file in yyfill

As I have discovered, the reason for the abort is because of the use of the noexcept specifier on all of the parser and related methods.
Per the spec ( http://en.cppreference.com/w/cpp/language/noexcept_spec ) runtimes must invoke std::terminate if an exception is being thrown through such a method. So therefore MSVC is actually acting correctly (for once).

The take away here, that I didn't really think of, is that setting failbit is inappropriate in most cases. Having read the documentation more thoroughly, it seems this failbit is more likely to give false-positives.

I have opened a pull request which adds a note to the documentation to this effect.

[nlohmann]

I merged #227.

@kevin--, is the issue fixed for you?

[kevin--]

Yes. There was no real bug, just a clash between failbit, getline reading 0 chars, and noexcept. Though I expect you should be able to reproduce this in other compilers.