Fix colliding mocking context ids

[otrempe]

Fixes https://github.com/eranpeer/FakeIt/issues/294

[otrempe]

Ok... I need to rework constExprHash so no C++14 features are used

[FranckRJ]

I haven't tried to see if it give the same result, but maybe something like this ?

constexpr size_t hash(const char* str, size_t val = 14695981039346656037ULL)
{
    return *str == '\0'
        ? val
        : hash(++str, val ^ static_cast<size_t>(*str) * 1099511628211ULL);
}

https://godbolt.org/z/7vqYqPTPh

EDIT: It probably won't give the same result because the order of evaluation of the parameters is unspecified, maybe ++str will evaluate first, maybe *str. To fix that we can simply write str + 1 instead of ++str, so the variable won't change its value.

EDIT 2: And it seems that the multiply operator take precedence over the bitwise XOR operator, yet again something that makes it non conforment (but easily fixable with parenthesis).

[coveralls]

Coverage decreased (-4.0e-05%) to 99.925% when pulling 2230a37a81a065cb2c0caf73cfb84ce1d5dc8ff6 on otrempe:Fix-CollidingMockingContextIds into 78ca536e6b32f11e2883d474719a447915e40005 on eranpeer:master.

[FranckRJ]

You need to add the new test files to https://github.com/eranpeer/FakeIt/blob/master/build/sources.mk as well, otherwise they won't run for GCC / Clang.

[otrempe]

Coverage decreased by 4.0e-05% :open_mouth: :laughing:

The Visual Studio build yields lots of warning C4307: '*': integral constant overflow However, Microsoft stopped issuing this warning starting with MSVC v19.23.

[otrempe]

I guess my .h/.cpp helper files need to be added to the sources.mk as well

[FranckRJ]

You're right, but only the .cpp.

[FranckRJ]

Thanks for the fix, I'll try to look more into it next week, I'll do some benchmark because I'm curious if it affect compilation time or not.

[FranckRJ]

I didn't see any measurable difference in compilation time with the fix for the FakeIt unit tests with GCC. I guess it's because our test files are small and the includes take a lot of time to compile, maybe with a test file that is a lot bigger (and pre-compiled header ?) we could notice a difference, or maybe the overhead is so insignificant that we wouldn't notice anything anyway. Either way it looks good to me.

[malcolmdavey]

If using precompiled headers (e.g. with VS) it might make the difference more noticeable (if fakeit.h is added to that).

[FranckRJ]

Superseded by #336. I went with a different approach that I explained in the PR.