wip(UseCython): Deprecate PY2 and PY3 options and introduce LANGUAGE_LEVEL

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

Author: jcfr

src/cython_cmake/cmake/UseCython.cmake

@@ -40,7 +40,16 @@
 #   generated, unless the C language is not enabled for the project; in this
 #   case, a C++ file is generated by default.
 #
-# ``PY2 | PY3``
+# ``LANGUAGE_LEVEL [2 | 3 | 3str]``
+#   Force compilation using either Python-2, Python-3 or Python-3str syntax and
+#   code semantics.
+#   By default, Python-3str syntax and semantics are used if the major version
+#   of Python found is 3 and Cython >=3 is used. Otherwise, Python-2 syntax and
+#   semantics are used.
+#   Using the Python-3str syntax and semantics means there cython does not assume
+#   unicode is used by by default for string literals under Python 2
+#
+# ``PY2 | PY3`` (deprecated)
 #   Force compilation using either Python-2 or Python-3 syntax and code
 #   semantics.  By default, Python-2 syntax and semantics are used if the major
 #   version of Python found is 2.  Otherwise, Python-3 syntax and semantics are
@@ -103,8 +112,8 @@ set(CYTHON_FLAGS "" CACHE STRING
 mark_as_advanced(CYTHON_ANNOTATE CYTHON_FLAGS)
 
 function(add_cython_target _name)
-  seT(_deprecated_options C CXX)
-  set(_options PY2 PY3)
+  set(_deprecated_options C CXX PY2 PY3)
+  set(_options )
   set(_one_value TARGET_LANGUAGE OUTPUT_VAR)
   set(_multi_value )
 
@@ -125,6 +134,16 @@ function(add_cython_target _name)
     endif()
   endif()
 
+  # Support deprecated options: PY2, PY3
+  if(NOT _args_LANGUAGE_LEVEL)
+    if(_args_PY2)
+      set(_args_LANGUAGE_LEVEL "2")
+    endif()
+    if(_args_PY3)
+      set(_args_LANGUAGE_LEVEL "3")
+    endif()
+  endif()
+
   list(GET _args_UNPARSED_ARGUMENTS 0 _arg0)
 
   # if provided, use _arg0 as the input file path
@@ -169,24 +188,21 @@ function(add_cython_target _name)
   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
-  set(_input_syntax "default")
-
-  if(_args_PY2)
-    set(_input_syntax "PY2")
+  # Set language level
+  set(_language_level ${_args_LANGUAGE_LEVEL})
+  if(NOT _args_LANGUAGE_LEVEL)
+    set(_language_level "3str")
+  else()
+    if(NOT _language_level MATCHES "^(2|3|3str)$")
+      message(FATAL_ERROR "LANGUAGE_LEVEL must be one of 2, 3, or 3str")
+    endif()
   endif()
 
-  if(_args_PY3)
-    set(_input_syntax "PY3")
-  endif()
+  set(_language_level_2_arg "-2")
+  set(_language_level_3_arg "-3")
+  set(_language_level_3str_arg "--3str")
 
-  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(_language_level_arg "${_language_level_${_language_level}_arg}")
 
   set(generated_file "${CMAKE_CURRENT_BINARY_DIR}/${_name}.${_target_language_extension}")
   set_source_files_properties(${generated_file} PROPERTIES GENERATED TRUE)
@@ -366,7 +382,7 @@ function(add_cython_target _name)
     ARGS
       ${_target_language_arg}
       ${include_directory_arg}
-      ${language_level_arg}
+      ${_language_level_arg}
       ${annotate_arg}
       ${cython_debug_arg}
       ${line_directives_arg}