[pyroot] Move JupyROOT files at build time.

Fix #17859.

Author: hageboeck

bindings/jupyroot/CMakeLists.txt

@@ -27,8 +27,17 @@ set(py_sources
   JupyROOT/magics/jsrootmagic.py
 )
 
-set(JupyROOTPySrcDir python/JupyROOT)
-file(COPY ${JupyROOTPySrcDir} DESTINATION ${localruntimedir})
+# Create a target that keeps JupyROOT source in the build tree up to date:
+set(JupyROOTPySrcDir ${CMAKE_CURRENT_SOURCE_DIR}/python/JupyROOT/)
+file(GLOB_RECURSE input_files RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} ${JupyROOTPySrcDir}/**)
+set(output_files ${input_files})
+list(TRANSFORM output_files REPLACE "python/" ${localruntimedir}/)
+
+add_custom_command(OUTPUT ${output_files}
+  COMMAND ${CMAKE_COMMAND} -E copy_directory ${JupyROOTPySrcDir} ${localruntimedir}/JupyROOT/
+  COMMENT "Copy JupyROOT"
+  DEPENDS ${input_files})
+add_custom_target(JupyROOT ALL DEPENDS ${output_files})
 
 # Compile .py files
 foreach(py_source ${py_sources})