[mlir][python] Add a warning for cmake version < 3.15.

[stellaraccident]

Summary

As discussed on discord, we have never actually been able to build with the project-wide published min version of 3.14.3. The buildbot that tests the Python configuration is currently pinned to 3.19.1, and there are a number of non-version/policy controlled features that Python building relies on that makes it unreliable with older versions. Some of the issues are pretty fundamental and I don't know how to do them on the older version. I think that, as an optional feature, at least advertising the PSA as in this patch is a good middle ground until the next project-wide CMake version bump.

[stellaraccident]

Move python config into a macro.

[mehdi_amini]

mlir/cmake/modules/MLIRDetectPythonEnv.cmake

9

Is this visible enough?
Should we instead make it an ERROR level?

[stephenneuendorffer]

mlir/cmake/modules/MLIRDetectPythonEnv.cmake

9

I think an ERROR would be better and recommend updating to 3.18 to fix the issue below?

[stellaraccident]

Comments.

[stellaraccident]

How's this?

[stellaraccident]

Landed in https://reviews.llvm.org/rG3d92722f74993969243d1400bc3257ca3d03902f (not sure why it didn't associate).

[mehdi_amini]

In D111689#3060393, @stellaraccident wrote:

Landed in https://reviews.llvm.org/rG3d92722f74993969243d1400bc3257ca3d03902f (not sure why it didn't associate).

The commit message does not have the "Differential Revision: https://..."

mlir/CMakeLists.txt

 # Python Bindings Configuration
 # Requires:
 #   The pybind11 library can be found (set with -DPYBIND_DIR=...)
 #   The python executable is correct (set with -DPython3_EXECUTABLE=...)
 #-------------------------------------------------------------------------------
 
 set(MLIR_ENABLE_BINDINGS_PYTHON 0 CACHE BOOL
        "Enables building of Python bindings.")
-
 if(MLIR_ENABLE_BINDINGS_PYTHON)
   include(MLIRDetectPythonEnv)
-  # After CMake 3.18, we are able to limit the scope of the search to just
-  # Development.Module. Searching for Development will fail in situations where
-  # the Python libraries are not available. When possible, limit to just
-  # Development.Module.
-  # See https://pybind11.readthedocs.io/en/stable/compiling.html#findpython-mode
-  if(CMAKE_VERSION VERSION_LESS "3.18.0")
-    set(_python_development_component Development)
-  else()
-    set(_python_development_component Development.Module)
-  endif()
-  find_package(Python3 ${LLVM_MINIMUM_PYTHON_VERSION}
-    COMPONENTS Interpreter ${_python_development_component} NumPy REQUIRED)
-  unset(_python_development_component)
-  message(STATUS "Found python include dirs: ${Python3_INCLUDE_DIRS}")
-  message(STATUS "Found python libraries: ${Python3_LIBRARIES}")
-  message(STATUS "Found numpy v${Python3_NumPy_VERSION}: ${Python3_NumPy_INCLUDE_DIRS}")
-  mlir_detect_pybind11_install()
-  find_package(pybind11 2.6 CONFIG REQUIRED)
-  message(STATUS "Found pybind11 v${pybind11_VERSION}: ${pybind11_INCLUDE_DIR}")
-  message(STATUS "Python prefix = '${PYTHON_MODULE_PREFIX}', "
-                 "suffix = '${PYTHON_MODULE_SUFFIX}', "
-                 "extension = '${PYTHON_MODULE_EXTENSION}")
+  mlir_configure_python_dev_packages()
 endif()
 
 include_directories( "include")
 include_directories( ${MLIR_INCLUDE_DIR})
 
 # Adding tools/mlir-tblgen here as calling add_tablegen sets some variables like
 # MLIR_TABLEGEN_EXE in PARENT_SCOPE which gets lost if that folder is included
 # from another directory like tools

mlir/cmake/modules/MLIRDetectPythonEnv.cmake

 # Macros and functions related to detecting details of the Python environment.
 
+# Finds and configures python packages needed to build MLIR Python bindings.
+macro(mlir_configure_python_dev_packages)
+  if(CMAKE_VERSION VERSION_LESS "3.15.0")
+  message(SEND_ERROR
+      "Building MLIR Python bindings is known to rely on CMake features "
+      "that require at least version 3.15. Recommend upgrading to 3.18+ "
+      "for full support. Detected current version: ${CMAKE_VERSION}")
+  endif()
+
+  # After CMake 3.18, we are able to limit the scope of the search to just
+  # Development.Module. Searching for Development will fail in situations where
+  # the Python libraries are not available. When possible, limit to just
+  # Development.Module.
+  # See https://pybind11.readthedocs.io/en/stable/compiling.html#findpython-mode
+  if(CMAKE_VERSION VERSION_LESS "3.18.0")
+    message(WARNING
+        "This version of CMake is not compatible with statically built Python "
+        "installations. If Python fails to detect below this may apply to you. "
+        "Recommend upgrading to at least CMake 3.18. "
+        "Detected current version: ${CMAKE_VERSION}"
+    )
+    set(_python_development_component Development)
+  else()
+    set(_python_development_component Development.Module)
+  endif()
+  find_package(Python3 ${LLVM_MINIMUM_PYTHON_VERSION}
+    COMPONENTS Interpreter ${_python_development_component} NumPy REQUIRED)
+  unset(_python_development_component)
+  message(STATUS "Found python include dirs: ${Python3_INCLUDE_DIRS}")
+  message(STATUS "Found python libraries: ${Python3_LIBRARIES}")
+  message(STATUS "Found numpy v${Python3_NumPy_VERSION}: ${Python3_NumPy_INCLUDE_DIRS}")
+  mlir_detect_pybind11_install()
+  find_package(pybind11 2.6 CONFIG REQUIRED)
+  message(STATUS "Found pybind11 v${pybind11_VERSION}: ${pybind11_INCLUDE_DIR}")
+  message(STATUS "Python prefix = '${PYTHON_MODULE_PREFIX}', "
+                 "suffix = '${PYTHON_MODULE_SUFFIX}', "
+                 "extension = '${PYTHON_MODULE_EXTENSION}")
+endmacro()
+
 # Detects a pybind11 package installed in the current python environment
 # and sets variables to allow it to be found. This allows pybind11 to be
 # installed via pip, which typically yields a much more recent version than
 # the OS install, which will be available otherwise.
 function(mlir_detect_pybind11_install)
   if(pybind11_DIR)
     message(STATUS "Using explicit pybind11 cmake directory: ${pybind11_DIR} (-Dpybind11_DIR to change)")
   else()