Add support for MS-MPI.

.appveyor.yml

@@ -76,6 +76,17 @@ install:
   - ps: If($Env:compiler -eq 'msys2-mingw') {(new-object Net.WebClient).DownloadFile('https://bootstrap.pypa.io/get-pip.py', 'C:\projects\meson\get-pip.py')}
   - cmd: if %compiler%==msys2-mingw ( %PYTHON% "C:\projects\meson\get-pip.py" )
   - cmd: if %compiler%==cygwin ( call ci\appveyor-install.bat )
+  - ps: |
+        If($Env:compiler -like 'msvc*') {
+          (new-object net.webclient).DownloadFile(
+            "https://download.microsoft.com/download/D/B/B/DBB64BA1-7B51-43DB-8BF1-D1FB45EACF7A/msmpisdk.msi",
+            "C:\projects\msmpisdk.msi")
+          c:\windows\system32\msiexec.exe /i C:\projects\msmpisdk.msi /quiet
+          (new-object net.webclient).DownloadFile(
+            "https://download.microsoft.com/download/D/B/B/DBB64BA1-7B51-43DB-8BF1-D1FB45EACF7A/MSMpiSetup.exe",
+            "C:\projects\MSMpiSetup.exe")
+          c:\projects\MSMpiSetup.exe -unattend -full
+        }
 
   # Install additional packages needed for all builds.
   - cmd: "%WRAPPER% %PYTHON% -m pip install codecov"

mesonbuild/dependencies/misc.py

@@ -342,6 +342,12 @@ class MPIDependency(ExternalDependency):
                     self.link_args = self._filter_link_args(result[2])
                     break
 
+        if not self.is_found and mesonlib.is_windows():
+            result = self._try_msmpi()
+            if result is not None:
+                self.is_found = True
+                self.version, self.compile_args, self.link_args = result
+
         if self.is_found:
             mlog.log('Dependency', mlog.bold(self.name), 'for', self.language, 'found:', mlog.green('YES'), self.version)
         else:
@@ -447,6 +453,35 @@ class MPIDependency(ExternalDependency):
 
             return version, args, args
 
+    def _try_msmpi(self):
+        if self.language == 'cpp':
+            # MS-MPI does not support the C++ version of MPI, only the standard C API.
+            return
+        if 'MSMPI_INC' not in os.environ:
+            return
+        incdir = os.environ['MSMPI_INC']
+        arch = detect_cpu_family(self.env.coredata.compilers)
+        if arch == 'x86':
+            if 'MSMPI_LIB32' not in os.environ:
+                return
+            libdir = os.environ['MSMPI_LIB32']
+            post = 'x86'
+        elif arch == 'x86_64':
+            if 'MSMPI_LIB64' not in os.environ:
+                return
+            libdir = os.environ['MSMPI_LIB64']
+            post = 'x64'
+        else:
+            return
+        if self.language == 'fortran':
+            return ('none',
+                    ['-I' + incdir, '-I' + os.path.join(incdir, post)],
+                    [os.path.join(libdir, 'msmpi.lib'), os.path.join(libdir, 'msmpifec.lib')])
+        else:
+            return ('none',
+                    ['-I' + incdir, '-I' + os.path.join(incdir, post)],
+                    [os.path.join(libdir, 'msmpi.lib')])
+
 
 class ThreadDependency(ExternalDependency):
     def __init__(self, environment, kwargs):

test cases/common/157 mpi/meson.build

@@ -1,5 +1,11 @@
 project('mpi', 'c', 'cpp')
 
+cc = meson.get_compiler('c')
+
+if build_machine.system() == 'windows' and cc.get_id() != 'msvc'
+  error('MESON_SKIP_TEST: MPI not available on Windows without MSVC.')
+endif
+
 mpic = dependency('mpi', language : 'c')
 exec = executable('exec',
   'main.c',
@@ -7,12 +13,15 @@ exec = executable('exec',
 
 test('MPI C', exec)
 
-mpicpp = dependency('mpi', language : 'cpp')
-execpp = executable('execpp',
-  'main.cpp',
-  dependencies : [mpicpp])
+if build_machine.system() != 'windows'
+  # C++ MPI not supported by MS-MPI used on AppVeyor.
+  mpicpp = dependency('mpi', language : 'cpp')
+  execpp = executable('execpp',
+    'main.cpp',
+    dependencies : [mpicpp])
 
-test('MPI C++', execpp)
+  test('MPI C++', execpp)
+endif
 
 if add_languages('fortran', required : false)
   mpifort = dependency('mpi', language : 'fortran')