From c465015e2f63d984b8086d60335a8fd6caf27b33 Mon Sep 17 00:00:00 2001
From: Hans Johnson <hans-johnson@uiowa.edu>
Date: Sat, 2 May 2026 08:37:25 -0500
Subject: [PATCH] COMP: Backport wrapping castxml genexes to CMake 3.22.1
 (issue #6191)
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PR #5842 introduced $<LIST:JOIN,$<LIST:TRANSFORM,…>> generator
expressions in itk_auto_load_submodules.cmake. Those operators
landed in CMake 3.27 (2023-07) but ITK's cmake_minimum_required is
3.22.1; on older CMake they silently expand to empty at
file(GENERATE) time, producing castxml.inc files with no
-I/-isystem/-D flags and breaking Python wrapping.

Rewrite the three affected sites with $<JOIN:list,glue> (CMake
3.0+), carrying the per-element wrapping in the glue string and
guarded by $<$<BOOL:property>:…> so an empty property emits
nothing. Generated castxml.inc bytes are byte-identical to the
3.27+ form for both populated and empty target properties.

Revert when ITK's CMake floor reaches 3.27 (block comment marks
the lines).
---
 Wrapping/macro_files/itk_auto_load_submodules.cmake | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/Wrapping/macro_files/itk_auto_load_submodules.cmake b/Wrapping/macro_files/itk_auto_load_submodules.cmake
index 527669a6368..4ca246ebc1e 100644
--- a/Wrapping/macro_files/itk_auto_load_submodules.cmake
+++ b/Wrapping/macro_files/itk_auto_load_submodules.cmake
@@ -119,17 +119,20 @@ function(generate_castxml_commandline_flags)
 
   foreach(_depend IN LISTS WRAPPER_LIBRARY_LINK_LIBRARIES)
     if(TARGET ${_depend})
+      # $<JOIN:list,glue> (CMake 3.0+) carries the per-element prefix in
+      # the glue string; $<$<BOOL:property>:…> guards against empty-property
+      # output of a stray "-I" / "-D" / "-isystem".
       set(
         CONFIG_CASTXML_INC_CONTENTS
-        "${CONFIG_CASTXML_INC_CONTENTS}$<LIST:JOIN,$<LIST:TRANSFORM,$<TARGET_PROPERTY:${_depend},INTERFACE_INCLUDE_DIRECTORIES>,REPLACE,^(.+)$,\"-I\\1\">,\n>\n"
+        "${CONFIG_CASTXML_INC_CONTENTS}$<$<BOOL:$<TARGET_PROPERTY:${_depend},INTERFACE_INCLUDE_DIRECTORIES>>:\"-I$<JOIN:$<TARGET_PROPERTY:${_depend},INTERFACE_INCLUDE_DIRECTORIES>,\"\n\"-I>\">\n"
       )
       set(
         CONFIG_CASTXML_INC_CONTENTS
-        "${CONFIG_CASTXML_INC_CONTENTS}$<LIST:JOIN,$<LIST:TRANSFORM,$<TARGET_PROPERTY:${_depend},INTERFACE_SYSTEM_INCLUDE_DIRECTORIES>,REPLACE,^(.+)$,\"-isystem\" \"\\1\">,\n>\n"
+        "${CONFIG_CASTXML_INC_CONTENTS}$<$<BOOL:$<TARGET_PROPERTY:${_depend},INTERFACE_SYSTEM_INCLUDE_DIRECTORIES>>:\"-isystem\" \"$<JOIN:$<TARGET_PROPERTY:${_depend},INTERFACE_SYSTEM_INCLUDE_DIRECTORIES>,\"\n\"-isystem\" \">\">\n"
       )
       set(
         CONFIG_CASTXML_INC_CONTENTS
-        "${CONFIG_CASTXML_INC_CONTENTS}$<LIST:JOIN,$<LIST:TRANSFORM,$<TARGET_PROPERTY:${_depend},INTERFACE_COMPILE_DEFINITIONS>,REPLACE,^(.+)$,\"-D\\1\">,\n>\n"
+        "${CONFIG_CASTXML_INC_CONTENTS}$<$<BOOL:$<TARGET_PROPERTY:${_depend},INTERFACE_COMPILE_DEFINITIONS>>:\"-D$<JOIN:$<TARGET_PROPERTY:${_depend},INTERFACE_COMPILE_DEFINITIONS>,\"\n\"-D>\">\n"
       )
     endif()
   endforeach()