feat: Simplify expecting only one input file

Co-authored-by: Jean-Christophe Fillion-Robin <[email protected]>

Author: henryiii

src/cython_cmake/cmake/UseCython.cmake

@@ -7,7 +7,7 @@
 # Create custom rules to generate the source code for a Python extension module
 # using cython.
 #
-#   Cython_compile_pyx(<pyx_file1> [<pyx_file2> ...]
+#   Cython_compile_pyx(<pyx_file>
 #                     [LANGUAGE C | CXX]
 #                     [CYTHON_ARGS <args> ...]
 #                     [OUTPUT_VARIABLE <OutputVariable>])
@@ -77,8 +77,13 @@ function(Cython_compile_pyx)
     ${ARGN}
     )
 
-  # Get source file location
-  set(_source_files ${_args_UNPARSED_ARGUMENTS})
+  # Get input
+  set(all_intput ${_args_UNPARSED_ARGUMENTS})
+  list(LENGTH all_intput input_length)
+  if(NOT input_length EQUAL 1)
+    message(FATAL_ERROR "One and only one input file must be specified, got '${all_intput}'")
+  endif()
+  list(GET all_intput 0 _source_file)
 
   # Set target language
   get_property(_languages GLOBAL PROPERTY ENABLED_LANGUAGES)
@@ -108,43 +113,38 @@ function(Cython_compile_pyx)
   set(_depfile ${generated_file}.dep)
   set(_depfile_arg "-M")
 
-  set(generated_files)
-
-  foreach(_source_file IN LISTS _source_files)
-    cmake_path(GET _source_file STEM _name)
-    set(generated_file "${CMAKE_CURRENT_BINARY_DIR}/${_name}.${_language_extension}")
-    set_source_files_properties(${generated_file} PROPERTIES GENERATED TRUE)
-
-    file(RELATIVE_PATH generated_file_relative
-        ${CMAKE_BINARY_DIR} ${generated_file})
-
-    set(comment "Generating ${_language} source ${generated_file_relative}")
-
-    get_source_file_property(pyx_location ${_source_file} LOCATION)
-
-    # Add the command to run the compiler.
-    add_custom_command(
-      OUTPUT ${generated_file}
-      COMMAND ${CYTHON_EXECUTABLE}
-      ARGS
-        ${_language_arg}
-        ${_args_CYTHON_ARGS}
-        ${_depfile_arg}
-        ${pyx_location}
-        --output-file ${generated_file}
-      DEPENDS
-        ${_source_file}
-      DEPFILE
-        ${_cython_depfile}
-      VERBATIM
-      COMMENT ${comment}
-    )
-    list(APPEND generated_files ${generated_file})
-  endforeach()
+  cmake_path(GET _source_file STEM _name)
+  set(generated_file "${CMAKE_CURRENT_BINARY_DIR}/${_name}.${_language_extension}")
+  set_source_files_properties(${generated_file} PROPERTIES GENERATED TRUE)
+
+  file(RELATIVE_PATH generated_file_relative
+      ${CMAKE_BINARY_DIR} ${generated_file})
+
+  set(comment "Generating ${_language} source ${generated_file_relative}")
+
+  get_source_file_property(pyx_location ${_source_file} LOCATION)
+
+  # Add the command to run the compiler.
+  add_custom_command(
+    OUTPUT ${generated_file}
+    COMMAND ${CYTHON_EXECUTABLE}
+    ARGS
+      ${_language_arg}
+      ${_args_CYTHON_ARGS}
+      ${_depfile_arg}
+      ${pyx_location}
+      --output-file ${generated_file}
+    DEPENDS
+      ${_source_file}
+    DEPFILE
+      ${_cython_depfile}
+    VERBATIM
+    COMMENT ${comment}
+  )
 
   if(_args_OUTPUT_VARIABLE)
     set(_output_variable ${_args_OUTPUT_VARIABLE})
-    set(${_output_variable} ${generated_files} PARENT_SCOPE)
+    set(${_output_variable} ${generated_file} PARENT_SCOPE)
   endif()
 
 endfunction()