Set PYBIND11_CPP1{4,7} macros for MSVC #841
Conversation
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I'm curious -- what happens when using the constexpr |
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It fails with: I didn't try investigating any further to try to fix it. |
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ok. give me time for investigating then. |
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Another MSVC annoyance: it looks like using std::enable_if_t;doesn't work with MSVC 2015. |
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A #792 failure, but otherwise passes now (same code, no failure). |
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pass all tests with and without -DPYBIND11_CPP_STANDARD=/std:c++latest on msvc 2017 |
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LGTM |
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can you then update documentation about -DPYBIND11_CPP_STANDARD=/std:c++latest ? |
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It's already documented, though it didn't mention the doesn't-do-anything-on-MSVC limitation (which this PR removes). I did reword things a bit, and added MSVC |
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It also changes the wording a bit to say that we explicitly target C++14 by default, rather than "the latest available," but mentions that it is subject to change to the latest available, which I think captures a little bit more clearly what we are doing. |
The PYBIND11_CPP14 macro started out as a guard for the compile-time path code in `descr.h`, but has since come to mean other things. This means that while the `descr.h` check has just checked the `PYBIND11_CPP14` macro, various other places now check `PYBIND11_CPP14 || _MSC_VER`. This reverses that by now setting the CPP14 macro when MSVC is trying to support C++14, but disabling the `descr.h` C++14 code (which still fails under MSVC 2017). The CPP17 macro also gets enabled when MSVC 2017 is compiling with /std:c++latest (the default is /std:c++14), which enables `std::optional` and `std::variant` support under MSVC.
Under MSVC we were ignoring PYBIND11_CPP_STANDARD and simply not passing any standard (which makes MSVC default to its C++14 mode). MSVC 2015u3 added the `/std:c++14` and `/std:c++latest` flags; the latter, under MSVC 2017, enables some C++17 features (such as `std::optional` and `std::variant`), so it is something we need to start supporting under MSVC. This makes the PYBIND11_CPP_STANDARD cmake variable work under MSVC, defaulting it to /std:c++14 (matching the default -std=c++14 for non-MSVC). It also adds a new appveyor test running under MSVC 2017 with /std:c++latest, which runs (and passes) the `std::optional`/`std::variant` tests. Also updated the documentation to clarify the c++ flags and add show MSVC flag examples.
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Squashed and merged. Re: |
We currently don't set
PYBIND11_CPP14or_CPP17for MSVC because MSVC doesn't support the code indescr.h. Originally, that's all the_CPP14flag guarded, but it now enables several other things as well (most of which are#ifdef CPP14 || MSVC). This flips that, settingCPP14andCPP17(the latter only when compiling under MSVC 2017 with/std:c++latest), then changing thedescr.hcode to requireCPP14 && !MSVC.This PR also enables the
PYBIND11_CPP_STANDARDcmake variable under MSVC, defaulting it to/std:c++14, then uses it to add a/std:c++latestappveyor job which runs the optional and variant tests.Fixes #833.