build: Upgrade to more modern python3 finding (#4288)

Latest versions of cmake are warning about FindPython being a deprecated
module, they recommend FindPython2 or FindPython3 instead. In master,
we're already python3 minimum, so go ahead and switch this to the modern
method.

This also seems to fully fix our recently broken CI on one of the Windows tests!

---------

Signed-off-by: Larry Gritz <lg@larrygritz.com>

CMakeLists.txt

@@ -246,8 +246,10 @@ if (NOT EMBEDPLUGINS AND NOT BUILD_OIIOUTIL_ONLY)
     endforeach ()
 endif ()
 
-if (USE_PYTHON AND Python_Development_FOUND AND NOT BUILD_OIIOUTIL_ONLY)
+if (USE_PYTHON AND Python3_Development_FOUND AND NOT BUILD_OIIOUTIL_ONLY)
     add_subdirectory (src/python)
+else ()
+    message (STATUS "Not building Python bindings: USE_PYTHON=${USE_PYTHON}, Python3_Development_FOUND=${Python3_Development_FOUND}")
 endif ()
 
 add_subdirectory (src/include)

src/cmake/pythonutils.cmake

@@ -19,8 +19,8 @@ endif ()
 # Python cannot be found, it will be a fatal error.
 macro (find_python)
     if (NOT VERBOSE)
-        set (PythonInterp_FIND_QUIETLY true)
-        set (PythonLibs_FIND_QUIETLY true)
+        set (PythonInterp3_FIND_QUIETLY true)
+        set (PythonLibs3_FIND_QUIETLY true)
     endif ()
 
     # Attempt to find the desired version, but fall back to other
@@ -32,23 +32,23 @@ macro (find_python)
             list (APPEND _req EXACT)
         endif ()
     endif ()
-    checked_find_package (Python ${PYTHON_VERSION}
+    checked_find_package (Python3 ${PYTHON_VERSION}
                           ${_req}
                           VERSION_MIN 3.7
                           COMPONENTS Interpreter Development
-                          PRINT Python_VERSION Python_EXECUTABLE
-                                Python_LIBRARIES
-                                Python_Development_FOUND
-                                Python_Interpreter_FOUND )
+                          PRINT Python3_VERSION Python3_EXECUTABLE
+                                Python3_LIBRARIES
+                                Python3_Development_FOUND
+                                Python3_Interpreter_FOUND )
 
     # The version that was found may not be the default or user
     # defined one.
-    set (PYTHON_VERSION_FOUND ${Python_VERSION_MAJOR}.${Python_VERSION_MINOR})
+    set (PYTHON_VERSION_FOUND ${Python3_VERSION_MAJOR}.${Python3_VERSION_MINOR})
 
     # Give hints to subsequent pybind11 searching to ensure that it finds
     # exactly the same version that we found.
-    set (PythonInterp_FIND_VERSION PYTHON_VERSION_FOUND)
-    set (PythonInterp_FIND_VERSION_MAJOR ${Python_VERSION_MAJOR})
+    set (PythonInterp3_FIND_VERSION PYTHON_VERSION_FOUND)
+    set (PythonInterp3_FIND_VERSION_MAJOR ${Python3_VERSION_MAJOR})
 
     if (NOT DEFINED PYTHON_SITE_DIR)
         set (PYTHON_SITE_DIR "${CMAKE_INSTALL_LIBDIR}/python${PYTHON_VERSION_FOUND}/site-packages/OpenImageIO")

src/cmake/testing.cmake

@@ -105,7 +105,7 @@ macro (oiio_add_tests)
                 set (_testname "${_testname}-broken")
             endif ()
 
-            set (_runtest ${Python_EXECUTABLE} "${CMAKE_SOURCE_DIR}/testsuite/runtest.py" ${_testdir})
+            set (_runtest ${Python3_EXECUTABLE} "${CMAKE_SOURCE_DIR}/testsuite/runtest.py" ${_testdir})
             if (MSVC_IDE)
                 set (_runtest ${_runtest} --devenv-config $<CONFIGURATION>
                                           --solution-path "${CMAKE_BINARY_DIR}" )

src/doc/CMakeLists.txt

@@ -21,7 +21,7 @@ endif()
 # generate man pages using txt2man and a tiny python script to munge the
 # result of "$tool --help"
 find_program(TXT2MAN txt2man)
-if (UNIX AND TXT2MAN AND Python_Interpreter_FOUND)
+if (UNIX AND TXT2MAN AND Python3_Interpreter_FOUND)
     message (STATUS "Unix man page documentation will be generated")
     set (cli_tools oiiotool iinfo maketx idiff igrep iconvert)
 
@@ -34,7 +34,7 @@ if (UNIX AND TXT2MAN AND Python_Interpreter_FOUND)
         list (APPEND manpage_files ${outfile})
         add_custom_command (OUTPUT ${outfile}
             COMMAND ${tool} --help |
-            ${Python_EXECUTABLE} "${documentation_SOURCE_DIR}/help2man_preformat.py" |
+            ${Python3_EXECUTABLE} "${documentation_SOURCE_DIR}/help2man_preformat.py" |
             ${TXT2MAN} -v OpenImageIO -s 1 -t ${tool} > ${outfile}
             DEPENDS ${tool} help2man_preformat.py)
     endforeach()

src/libOpenImageIO/CMakeLists.txt

@@ -120,7 +120,7 @@ target_compile_definitions(OpenImageIO
               PRIVATE
                   OIIO_FREETYPE_VERSION="${FREETYPE_VERSION_STRING}"
                   OIIO_OpenCV_VERSION="${OpenCV_VERSION}"
-                  OIIO_PYTHON_VERSION="${Python_VERSION}"
+                  OIIO_PYTHON_VERSION="${Python3_VERSION}"
                   OIIO_QT_VERSION="${Qt6_VERSION}${Qt5_VERSION}"
                   OIIO_TBB_VERSION="${TBB_VERSION}"
              )