Do not assume that msys is on the C drive.

.github/workflows/windows.yml

@@ -31,6 +31,7 @@ jobs:
           curl
           git
           mingw-w64-ucrt-x86_64-gcc
+          mingw-w64-ucrt-x86_64-python
           mingw-w64-ucrt-x86_64-gtkmm3
           mingw-w64-ucrt-x86_64-boost    
           mingw-w64-ucrt-x86_64-sqlite3

CMakeLists.txt

@@ -296,8 +296,8 @@ if(WIN32)
   # Set the PYTHON_EXECUTABLE variable explicitly to ensure
   # that we use the msys2 python, not anything else that may
   # be floating around too (like on github runners...).
-  set(Python_EXECUTABLE "/usr/bin/python3")
-  set(PYTHON_EXECUTABLE "/usr/bin/python3")  
+#  set(Python_EXECUTABLE "/usr/bin/python3")
+#  set(PYTHON_EXECUTABLE "/usr/bin/python3")  
 endif()
 find_package(Python COMPONENTS Interpreter Development)
 find_package(pybind11 CONFIG)
@@ -475,33 +475,33 @@ if(WIN32)
   install(DIRECTORY deps/ DESTINATION . FILES_MATCHING PATTERN "*.dll")      
 
   # And install a few more which, for reasons unknown, are not reported by dll.
-  install(FILES C:/msys64/ucrt64/bin/libcharset-1.dll                DESTINATION .)
-  install(FILES C:/msys64/ucrt64/bin/librsvg-2-2.dll                 DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libxml2-2.dll                   DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/liblzma-5.dll                   DESTINATION .)
+  winstall(FILES /ucrt64/bin/libcharset-1.dll                DESTINATION .)
+  winstall(FILES /ucrt64/bin/librsvg-2-2.dll                 DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libxml2-2.dll                   DESTINATION .)  
+  winstall(FILES /ucrt64/bin/liblzma-5.dll                   DESTINATION .)
   # FIXME: these can be found by running ldd on numpy and matplotlib dlls.
-  install(FILES C:/msys64/ucrt64/bin/libopenblas.dll                 DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libgomp-1.dll                   DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libgfortran-5.dll               DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libquadmath-0.dll               DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libsharpyuv-0.dll               DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libjpeg-8.dll                   DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libtiff-6.dll                   DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libdeflate.dll                  DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libjbig-0.dll                   DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libLerc.dll                     DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libwebp-7.dll                   DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libzstd.dll                     DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/imagequant.dll                  DESTINATION .)  
-  install(FILES C:/msys64/ucrt64/bin/libopenjp2-7.dll                DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libopenblas.dll                 DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libgomp-1.dll                   DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libgfortran-5.dll               DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libquadmath-0.dll               DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libsharpyuv-0.dll               DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libjpeg-8.dll                   DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libtiff-6.dll                   DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libdeflate.dll                  DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libjbig-0.dll                   DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libLerc.dll                     DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libwebp-7.dll                   DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libzstd.dll                     DESTINATION .)  
+  winstall(FILES /ucrt64/bin/imagequant.dll                  DESTINATION .)  
+  winstall(FILES /ucrt64/bin/libopenjp2-7.dll                DESTINATION .)  
 
   # We need gdbus to setup the dbus, needed by Glib, otherwise anything
   # gtk-related will just bail out at start. We also need the helper
   # program to spawn programs using Glib.
-  install(FILES C:/msys64/ucrt64/bin/gdbus.exe                       DESTINATION .)
-  install(FILES C:/msys64/ucrt64/bin/gspawn-win64-helper.exe         DESTINATION .)
-  install(FILES C:/msys64/ucrt64/bin/gspawn-win64-helper-console.exe DESTINATION .)
-  install(FILES C:/msys64/ucrt64/bin/gdk-pixbuf-query-loaders.exe    DESTINATION .)
+  winstall(FILES /ucrt64/bin/gdbus.exe                       DESTINATION .)
+  winstall(FILES /ucrt64/bin/gspawn-win64-helper.exe         DESTINATION .)
+  winstall(FILES /ucrt64/bin/gspawn-win64-helper-console.exe DESTINATION .)
+  winstall(FILES /ucrt64/bin/gdk-pixbuf-query-loaders.exe    DESTINATION .)
 endif()
 
 #---------------------------------------------------------------------------

cmake/functions.cmake

@@ -21,4 +21,9 @@ macro(install_directory_permissions DIR)
   )
 endmacro()
 
-
+# Macro just like `install`, but converting the path from a unix
+# path to a windows path using `cygpath`.
+macro(install_for_win TMP1 FILE TMP2 DEST)
+  execute_process(COMMAND cygpath -m ${FILE} OUTPUT_VARIABLE WFILE)
+  install(FILES ${WFILE} DESTINATION ${DEST})
+endmacro()