Execute tests with clang sanitizers

[nlohmann]

Issue #389 could have been prevented if the UB sanitizer had been used during continuous integration. We shall add a Travis job for this if possible.

Required flags:

-g -O2 -fsanitize=address -fsanitize=undefined -fno-omit-frame-pointer

[nlohmann]

Related: http://travistoptips.blogspot.de/2015/11/default-template.html

[nlohmann]

For some reason, the code does not compile with sanitizers switched on, see https://travis-ci.org/nlohmann/json/jobs/183684093.

[Daniel599]

Hi, I think I found out why it didn't compile (I had the same problem on my Ubuntu 14.04)
I used clang++-3.4 and I think that by default it uses gcc's stdlib (which is gcc 4.8 on Ubuntu 14.04),
now this stdlib isn't fully c++11 compliant, e.g vector::insert( iterator pos, InputIt first, InputIt last) returns void, and I think that your travis-ci has the same problem since it is Ubuntu 14.04 also.

by adding : -stdlib=libc++
clang_sanitize: clean CXX=clang++ CXXFLAGS="-stdlib=libc++ -g -O2 -fsanitize=address -fsanitize=undefined -fno-omit-frame-pointer" $(MAKE)

It compiled but seems it didn't run the tests, I will try to work on it and give you a PR, but since it my first time here, I need to find out how.
Anyway, I hope it helps.

[Daniel599]

I was able to make it compile and run on travis-ci
https://travis-ci.org/Daniel599/json/jobs/186527572#L5753
but sadly some of the errors don;t give callstack so I don't know how to fix them.
Should I make a PR or investigate more?

[nlohmann]

Thanks @Daniel599, I shall try this in a feature branch.

[nlohmann]

@Daniel599 I can no reproduce your observation: https://travis-ci.org/nlohmann/json/jobs/186632504#L5756

The test case that triggers the undefined behavior is a bit weird anyway. It is an allocator which can be configured to throw a bad_alloc in some situations. Unfortunately, I cannot reproduce the error on my machine yet.

[Daniel599]

@nlohmann I have been thinking about it some more, and I think that something here is odd;
by going with my logic above (clang uses gcc-4.8's stdlibc++), none of your clang builds should have work,
but they do, so I think i`m missing something.

Please note that there is another run-time error in unit-algorithms (but seems to be only with clang's libc++) .
Anyway, I have been trying to run clang_sanitize on my other PC (ubuntu 16.04 with gcc 5.4),
but there is a bug in libc++ there
so I tried with libstdc++ of gcc 5.4, and it works :), I think that your code has 0 errors with libstdc++,
trying on travis now (by adding package g++-6 to apt).

but considering my first lines of this comment, I`m still not sure that's the right way.
sorry for long post.