wip(UseCython): Deprecate C and CXX option and introduce TARGET_LANGUAGE

Co-authored-by: Vyas Ramasubramani <[email protected]>

Author: jcfr

src/cython_cmake/cmake/UseCython.cmake

@@ -30,7 +30,12 @@
 #
 # Options:
 #
-# ``C | CXX``
+# ``TARGET_LANGUAGE [C | CXX]``
+#   Force the generation of either a C or C++ file. By default, a C file is
+#   generated, unless the C language is not enabled for the project; in this
+#   case, a C++ file is generated by default.
+#
+# ``C | CXX`` (deprecated)
 #   Force the generation of either a C or C++ file.  By default, a C file is
 #   generated, unless the C language is not enabled for the project; in this
 #   case, a C++ file is generated by default.
@@ -97,23 +102,29 @@ set(CYTHON_FLAGS "" CACHE STRING
     "Extra flags to the cython compiler.")
 mark_as_advanced(CYTHON_ANNOTATE CYTHON_FLAGS)
 
-set(CYTHON_CXX_EXTENSION "cxx")
-set(CYTHON_C_EXTENSION "c")
-
-get_property(languages GLOBAL PROPERTY ENABLED_LANGUAGES)
-
 function(add_cython_target _name)
-  set(_options C CXX PY2 PY3)
-  set(_one_value OUTPUT_VAR)
+  seT(_deprecated_options C CXX)
+  set(_options PY2 PY3)
+  set(_one_value TARGET_LANGUAGE OUTPUT_VAR)
   set(_multi_value )
 
   cmake_parse_arguments(_args
-    "${_options}"
+    "${_options} ${_deprecated_options}"
     "${_one_value}"
     "${_multi_value}"
     ${ARGN}
     )
 
+  # Support deprecated options: C, CXX
+  if(NOT _args_TARGET_LANGUAGE)
+    if(_args_C)
+      set(_args_TARGET_LANGUAGE "C")
+    endif()
+    if(_args_CXX)
+      set(_args_TARGET_LANGUAGE "CXX")
+    endif()
+  endif()
+
   list(GET _args_UNPARSED_ARGUMENTS 0 _arg0)
 
   # if provided, use _arg0 as the input file path
@@ -135,22 +146,28 @@ function(add_cython_target _name)
     endif()
   endif()
 
-
-  if("C" IN_LIST languages)
-    set(target_language "C")
-  elseif("CXX" IN_LIST languages)
-    set(target_language "CXX")
+  # Set target language
+  get_property(_languages GLOBAL PROPERTY ENABLED_LANGUAGES)
+  set(_target_language ${_args_TARGET_LANGUAGE})
+  if(NOT _target_language)
+    if("C" IN_LIST _languages)
+      set(_target_language "C")
+    elseif("CXX" IN_LIST _languages)
+      set(_target_language "CXX")
+    endif()
   else()
-    message(FATAL_ERROR "Either C or CXX must be enabled to use Cython")
+    if(NOT _target_language MATCHES "^(C|CXX)$")
+      message(FATAL_ERROR "TARGET_LANGUAGE must be one of C or CXX")
+    endif()
   endif()
 
-  if(_args_C)
-    set(target_language "C")
-  endif()
+  set(_target_language_C_arg "")
+  set(_target_language_C_extension "c")
+  set(_target_language_CXX_arg "--cplus")
+  set(_target_language_CXX_extension "cxx")
 
-  if(_args_CXX)
-    set(target_language "CXX")
-  endif()
+  set(_target_language_arg ${_target_language_${_target_language}_arg})
+  set(_target_language_extension ${_target_language_${_target_language}_extension})
 
   # Doesn't select an input syntax - Cython
   # defaults to 2 for Cython 2 and 3 for Cython 3
@@ -164,21 +181,14 @@ function(add_cython_target _name)
     set(_input_syntax "PY3")
   endif()
 
-  set(cxx_arg "")
-  set(extension "c")
-  if(target_language STREQUAL "CXX")
-    set(cxx_arg "--cplus")
-    set(extension "cxx")
-  endif()
-
   set(language_level_arg "")
   if(_input_syntax STREQUAL "PY2")
     set(language_level_arg "-2")
   elseif(_input_syntax STREQUAL "PY3")
     set(language_level_arg "-3")
   endif()
 
-  set(generated_file "${CMAKE_CURRENT_BINARY_DIR}/${_name}.${extension}")
+  set(generated_file "${CMAKE_CURRENT_BINARY_DIR}/${_name}.${_target_language_extension}")
   set_source_files_properties(${generated_file} PROPERTIES GENERATED TRUE)
 
   set(_output_var ${_name})
@@ -190,7 +200,7 @@ function(add_cython_target _name)
   file(RELATIVE_PATH generated_file_relative
       ${CMAKE_BINARY_DIR} ${generated_file})
 
-  set(comment "Generating ${target_language} source ${generated_file_relative}")
+  set(comment "Generating ${_target_language} source ${generated_file_relative}")
   set(cython_include_directories "")
   set(pxd_dependencies "")
   set(c_header_dependencies "")
@@ -354,7 +364,7 @@ function(add_cython_target _name)
     OUTPUT ${generated_file}
     COMMAND ${CYTHON_EXECUTABLE}
     ARGS
-      ${cxx_arg}
+      ${_target_language_arg}
       ${include_directory_arg}
       ${language_level_arg}
       ${annotate_arg}
@@ -367,7 +377,7 @@ function(add_cython_target _name)
       ${_source_file}
       ${pxd_dependencies}
     IMPLICIT_DEPENDS
-      ${target_language}
+      ${_target_language}
       ${c_header_dependencies}
     COMMENT ${comment}
   )