[mlir][python] Add install target for MLIR Python sources.

[JackW]

Motivating use case of this commit is https://github.com/openxla/iree/pull/14411. Projects which take an installation dependency on MLIR sometimes need to have access to the source of the Python bindings to build against them. However, before, there was no way of installing these bindings.

[stellaraccident]

Thank you for catching/fixing this! Do you need help landing?

[JackW]

In D155362#4507445, @stellaraccident wrote:

Thank you for catching/fixing this! Do you need help landing?

Yes. Thank you.

mlir/cmake/modules/AddMLIRPython.cmake

foreach(source_relative_path ${ARGN})
     # Transform "a/b/c.py" -> "${install_prefix}/a/b" for installation.
     get_filename_component(
       dest_relative_dir "${source_relative_path}" DIRECTORY
       BASE_DIR "${source_root_dir}"
     )
     install(
       FILES "${source_root_dir}/${source_relative_path}"
       DESTINATION "${destination}/${dest_relative_dir}"
-      COMPONENT "${name}"
+      COMPONENT mlir-python-sources
     )
   endforeach()
-  get_target_export_arg(${name} MLIR export_to_mlirtargets UMBRELLA mlir-libraries)
+  get_target_export_arg(${name} MLIR export_to_mlirtargets
+    UMBRELLA mlir-python-sources)
   install(TARGETS ${name}
-    COMPONENT ${name}
+    COMPONENT mlir-python-sources
     ${export_to_mlirtargets}
   )
 endfunction()
 
 # Function: add_mlir_python_modules
 # Adds python modules to a project, building them from a list of declared
 # source groupings (see declare_mlir_python_sources and
 # declare_mlir_python_extension). One of these must be called for each

mlir/python/CMakeLists.txt

DECLARED_HEADERS
     MLIRPythonCAPI.HeaderSources
   DECLARED_SOURCES
     MLIRPythonSources
     MLIRPythonExtension.RegisterEverything
     ${_ADDL_TEST_SOURCES}
 )
 
 ################################################################################
+# Custom targets.
+################################################################################
+
+_flatten_mlir_python_targets(mlir_python_sources_deps MLIRPythonSources)
+add_custom_target("mlir-python-sources" DEPENDS ${mlir_python_sources_deps})
+if(NOT LLVM_ENABLE_IDE)
+  add_llvm_install_targets(install-mlir-python-sources
+    DEPENDS mlir-python-sources
+    COMPONENT mlir-python-sources
+  )
+endif()
+
+################################################################################
 # The fully assembled package of modules.
 # This must come last.
 ################################################################################
 
 add_mlir_python_modules(MLIRPythonModules
   ROOT_PREFIX "${MLIR_BINARY_DIR}/python_packages/mlir_core/mlir"
   INSTALL_PREFIX "python_packages/mlir_core/mlir"
   DECLARED_SOURCES
     MLIRPythonSources
     MLIRPythonExtension.RegisterEverything
     ${_ADDL_TEST_SOURCES}
   COMMON_CAPI_LINK_LIBS
     MLIRPythonCAPI
 )