Add test forcing newer MSVC/VC++ compilers supporting modern C++ in Python 2.7/3.5

CI.md

@@ -1,11 +1,12 @@
 This is a summary of the Python versions and platforms covered by the different CI platforms:
 
-|          | 3.5              | 3.6              | 3.7                                               | 3.8              |
-|----------|------------------|------------------|---------------------------------------------------|------------------|
-| Linux    | Travis CI        | CircleCI         | AppVeyor / GitHub Actions                         | Azure Pipelines  |
-| macOS    | Azure Pipelines  | CircleCI         | AppVeyor / Travis CI¹ / CircleCI / GitHub Actions | Azure Pipelines  |
-| Windows  | TravisCI         | Azure Pipelines  | AppVeyor / GitHub Actions                         | Azure Pipelines  |
+|          | 3.5              | 3.6              | 3.7                                                | 3.8              |
+|----------|------------------|------------------|----------------------------------------------------|------------------|
+| Linux    | Travis CI        | CircleCI         | AppVeyor² / GitHub Actions                         | Azure Pipelines  |
+| macOS    | Azure Pipelines  | CircleCI         | AppVeyor² / Travis CI¹ / CircleCI / GitHub Actions | Azure Pipelines  |
+| Windows  | TravisCI         | Azure Pipelines  | AppVeyor² / GitHub Actions                         | Azure Pipelines  |
 
 > ¹ Python version not really pinned, but dependent on the (default) version of image used.
+> ² AppVeyor only runs the "basic" test to reduce load.
 
 Non-x86 architectures are covered on Travis CI using Python 3.5.

docs/cpp_standards.md

@@ -30,6 +30,14 @@ For more details see https://en.cppreference.com/w/cpp/compiler_support, https:/
 
 ## Windows and Python 2.7
 
-Visual C++ for Python 2.7 does not support modern standards of C++. When building on Appveyor, you will need to either use the "Visual Studio 2017" or "Visual Studio 2019" image, but Python 2.7 is not supported on these images - skip it by setting `CIBW_SKIP=cp27-win*`.
+Visual C++ for Python 2.7 does not support modern C++ standards (i.e., C++11 and later). When building on Appveyor, you will need to either use the "Visual Studio 2017" or "Visual Studio 2019" image, but Python 2.7 is not supported on these images - skip it by setting `CIBW_SKIP=cp27-win*`.
 
-There is an optional workaround for this, though: the pybind11 project argues and shows that it is [possible to compile Python 2.7 extension with a newer compiler](https://pybind11.readthedocs.io/en/stable/faq.html#working-with-ancient-visual-studio-2008-builds-on-windows) and has an example project showing how to do this: https://github.com/pybind/python_example. The main catch is that a user might need to install a newer "Microsoft Visual C++ Redistributable", since the newer C++ standard libraries are not included by default with the Python 2.7 installation.
+There is an optional workaround for this, though: the pybind11 project argues and shows that it is [possible to compile Python 2.7 extension with a newer compiler](https://pybind11.readthedocs.io/en/stable/faq.html#working-with-ancient-visual-studio-2008-builds-on-windows) and has an example project showing how to do this: https://github.com/pybind/python_example. The main catch is that a user might need to install [a newer "Microsoft Visual C++ Redistributable"](https://support.microsoft.com/en-us/help/2977003/the-latest-supported-visual-c-downloads), since the newer C++ standard library's binaries are not included by default with the Python 2.7 installation.
+
+Forcing `distutils` or `setuptools` to use a more recent version of MSVC that supports modern C++ can be done in the following way:
+
+1. Set the environment variables `DISTUTILS_USE_SDK=1` and `MSSdk=1`. These two environment variables will tell `distutils`/`setuptools` to not search and set up a build environment that uses Visual C++ for Python 2.7 (aka. MSVC 9).
+2. Set up the build Visual Studio build environment you want to use, making sure that e.g. `PATH` contains `cl`, `link`, etc.
+    - Usually, this can be done through `vcvarsall.bat x86` or `vcvarsall.bat x64`. The exact location of this file depends on the installation, but the default path for VS 2019 Community (e.g. used in AppVeyor's `Visual Studio 2019` image) is `C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat`. **Note**: `vcvarsall.bat` changes the environment variables, so this cannot be run in a subprocess/subshell and consequently running `vsvarsall.bat` in `CIBW_BEFORE_BUILD` does not have any effect.
+    - In Azure Pipelines, [a `VSBuild` task is available](https://docs.microsoft.com/en-us/azure/devops/pipelines/tasks/build/visual-studio-build) and GitHub Actions has [an action `microsoft/setup-msbuild`](https://github.com/microsoft/setup-msbuild) that help setting up the Visual Studio environment.
+3. Next, call `cibuildwheel`. Unfortunately, MSVC has separate toolchains for compiling 32-bit and 64-bit, so you will need to run `cibuildwheel` twice: once with `CIBW_BUILD=*-win32` after setting up the `x86` build environment, and once with `CIBW_BUILD=*-win_amd64` in a `x64` enviroment (see previous step).

test/10_cpp_standards/cibuildwheel_test.py

@@ -7,7 +7,7 @@
 project_dir = os.path.dirname(__file__)
 
 
-def test_cpp11(tmp_path):
+def test_cpp11():
     # This test checks that the C++11 standard is supported
 
     # VC++ for Python 2.7 does not support modern standards
@@ -25,14 +25,12 @@ def test_cpp14():
 
     # VC++ for Python 2.7 does not support modern standards
     # The manylinux1 docker image does not have a compiler which supports C++11
-    # Python 3.4 and 3.5 are compiled with MSVC 10, which does not support C++14
-    add_env = {'CIBW_SKIP': 'cp27-win* pp27-win32 cp35-win*', 'CIBW_ENVIRONMENT': 'STANDARD=14'}
+    add_env = {'CIBW_SKIP': 'cp27-win* pp27-win32', 'CIBW_ENVIRONMENT': 'STANDARD=14'}
 
     actual_wheels = utils.cibuildwheel_run(project_dir, add_env=add_env)
     expected_wheels = [w for w in utils.expected_wheels('spam', '0.1.0')
                        if 'cp27-cp27m-win' not in w
-                       and 'pp27-pypy_73-win32' not in w
-                       and 'cp35-cp35m-win' not in w]
+                       and 'pp27-pypy_73-win32' not in w]
 
     assert set(actual_wheels) == set(expected_wheels)
 
@@ -42,20 +40,67 @@ def test_cpp17():
 
     # Python and PyPy 2.7 use the `register` keyword which is forbidden in the C++17 standard
     # The manylinux1 docker image does not have a compiler which supports C++11
-    # Python 3.5 and PyPy 3.6 are compiled with MSVC 10, which does not support C++17
     if os.environ.get('APPVEYOR_BUILD_WORKER_IMAGE', '') == 'Visual Studio 2015':
         pytest.skip('Visual Studio 2015 does not support C++17')
 
-    add_env = {'CIBW_SKIP': 'cp27-win* pp27-win32 cp35-win* pp36-win32', 'CIBW_ENVIRONMENT': 'STANDARD=17'}
+    add_env = {'CIBW_SKIP': 'cp27-win* pp27-win32', 'CIBW_ENVIRONMENT': 'STANDARD=17'}
 
     if utils.platform == 'macos':
         add_env['MACOSX_DEPLOYMENT_TARGET'] = '10.13'
 
     actual_wheels = utils.cibuildwheel_run(project_dir, add_env=add_env)
     expected_wheels = [w for w in utils.expected_wheels('spam', '0.1.0', macosx_deployment_target='10.13')
                        if 'cp27-cp27m-win' not in w
-                       and 'pp27-pypy_73-win32' not in w
-                       and 'cp35-cp35m-win' not in w
-                       and 'pp36-pypy36_pp73-win32' not in w]
+                       and 'pp27-pypy_73-win32' not in w]
+
+    assert set(actual_wheels) == set(expected_wheels)
+
+
+def test_cpp17_py27_modern_msvc_workaround():
+    # This test checks the workaround for building Python 2.7 wheel with MSVC 14
+
+    if utils.platform != 'windows':
+        pytest.skip('the test is only relevant to the Windows build')
+
+    if os.environ.get('APPVEYOR_BUILD_WORKER_IMAGE', '') == 'Visual Studio 2015':
+        pytest.skip('Visual Studio 2015 does not support C++17')
+
+    # VC++ for Python 2.7 (i.e., MSVC 9) does not support modern standards
+    # This is a workaround which forces distutils/setupstools to a newer version
+    # Wheels compiled need a more modern C++ redistributable installed, which is not
+    # included with Python: see documentation for more info
+    # DISTUTILS_USE_SDK and MSSdk=1 tell distutils/setuptools that we are adding
+    # MSVC's compiler, tools, and libraries to PATH ourselves
+    add_env = {'CIBW_ENVIRONMENT': 'STANDARD=17',
+               'DISTUTILS_USE_SDK': '1', 'MSSdk': '1'}
+
+    # Use existing setuptools code to run Visual Studio's vcvarsall.bat and get the
+    # necessary environment variables, since running vcvarsall.bat in a subprocess
+    # does not keep the relevant environment variables
+    # There are different environment variables for 32-bit/64-bit targets, so we
+    # need to run cibuildwheel twice, once for 32-bit with `vcvarsall.bat x86, and
+    # once for 64-bit with `vcvarsall.bat x64`
+    # In a normal CI setup, just run vcvarsall.bat before running cibuildwheel and set
+    # DISTUTILS_USE_SDK and MSSdk
+    import setuptools
+
+    def add_vcvars(prev_env, platform):
+        vcvarsall_env = setuptools.msvc.msvc14_get_vc_env(platform)
+        env = prev_env.copy()
+        for vcvar in ['path', 'include', 'lib']:
+            env[vcvar] = vcvarsall_env[vcvar]
+        return env
+
+    add_env_x86 = add_vcvars(add_env, 'x86')
+    add_env_x86['CIBW_BUILD'] = '?p27-win32'
+    actual_wheels = utils.cibuildwheel_run(project_dir, add_env=add_env_x86)
+
+    add_env_x64 = add_vcvars(add_env, 'x64')
+    add_env_x64['CIBW_BUILD'] = 'cp27-win_amd64'
+    actual_wheels += utils.cibuildwheel_run(project_dir, add_env=add_env_x64)
+
+    expected_wheels = [w for w in utils.expected_wheels('spam', '0.1.0')
+                       if 'cp27-cp27m-win' in w
+                       or 'pp27-pypy_73-win32' in w]
 
     assert set(actual_wheels) == set(expected_wheels)