Add Cygwin build on AppVeyor

.github/appveyor.yml

@@ -5,6 +5,7 @@ branches:
     - master
     - /\d\.\d/
     - buildbot-custom
+    - appveyor-cygwin
 cache:
   - externals -> PCbuild
 before_build:
@@ -28,11 +29,42 @@ before_build:
 
 
 build_script:
-  - cmd: PCbuild\build.bat -e -p x64
-  - cmd: PCbuild\amd64\python.exe -m test.pythoninfo
+- ps: |
+    if ($env:PLATFORM -eq "Win32") {
+        PCbuild\build.bat -e -p x64
+        PCbuild\amd64\python.exe -m test.pythoninfo
+    } elseif ($env:PLATFORM -eq "Cygwin64") {
+        . .github\cygwin.ps1
+        Cygwin cygcheck -s
+        Cygwin curl -s --output apt-cyg https://raw.githubusercontent.com/transcode-open/apt-cyg/master/apt-cyg
+        Cygwin chmod +x apt-cyg
+        Cygwin ./apt-cyg install libcrypt-devel libffi-devel zlib-devel "2>&1"
+        Cygwin ./configure
+        Cygwin make -j4
+        Cygwin ./python.exe -m test.pythoninfo
+    }
 test_script:
-  - cmd: PCbuild\rt.bat -x64 -q -uall -u-cpu -u-largefile -rwW --slowest --timeout=1200 --fail-env-changed -j0
+- ps: |
+    if ($env:PLATFORM -eq "Win32") {
+        PCbuild\rt.bat -x64 -q -uall -u-cpu -u-largefile -rwW --slowest --timeout=1200 --fail-env-changed -j0
+        if ($LastExitCode -eq 0) {
+            $host.SetShouldExit(0)
+        }
+    } elseif ($env:PLATFORM -eq "Cygwin64") {
+        . .github\cygwin.ps1
+        # For now, skip tests that are failing locally
+        # Later we will want to expand this to more closely resemble hwo the
+        # tests are run for Linux on Travis-CI
+        Cygwin ./python.exe -E -Wd -m test -w --timeout=1200 --fail-env-changed -j0 -x test_argparse -x test_asyncio -x test_asyncore -x test_bufio -x test_c_locale_coercion -x test_concurrent_futures -x test_dbm_dumb -x test_distutils -x test_file -x test_file_eintr -x test_fileio -x test_grp -x test_httpservers -x test_import -x test_io -x test_ioctl -x test_largefile -x test_logging -x test_math -x test_memoryio -x test_mmap -x test_multiprocessing_fork -x test_multiprocessing_forkserver -x test_multiprocessing_main_handling -x test_multiprocessing_spawn -x test_os -x test_pathlib -x test_posix -x test_pwd -x test_py_compile -x test_resource -x test_selectors -x test_shutil -x test_signal -x test_socket -x test_socketserver -x test_ssl -x test_stat -x test_subprocess -x test_support -x test_tarfile -x test_tempfile -x test_univnewlines -x test_urllib -x test_utf8_mode -x test_venv -x test_zipfile
+    }
 environment:
   HOST_PYTHON: C:\Python36\python.exe
 image:
   - Visual Studio 2017
+platform:
+    - Win32
+    - Cygwin64
+matrix:
+    fast_finish: true
+    allow_failures:
+        - platform: Cygwin64

.github/cygwin.ps1

@@ -0,0 +1,10 @@
+function Cygwin {
+    $cygbin = "C:\\cygwin64\\bin"
+    $project_path = & "$cygbin\\cygpath" -u -a $env:APPVEYOR_BUILD_FOLDER
+    $cmd = ("C:\\cygwin64\\bin\\bash.exe -lc " +`
+        "'cd $project_path; $($args -join " ")'")
+    Invoke-Expression $cmd
+    if ($LastExitCode -ne 0) {
+        $host.SetShouldExit($LastExitCode)
+    }
+}